List of Publications, including abstracts
The action of a-mercaptocarboxylic acid on unsaturated ß-aminocarboxylic acid esters. Asinger, Friedrich; Fabian, Juergen. Tech. Hochschule, Dresden, Germany. Monatshefte fuer Chemie (1962), 93 282-91.
a-Mereaptocarboxylic acids and their esters refluxed in tech. CHCl3 with b-aminocrotonic ester analogs witn tile azeotropic removal of H2O yield 2-carbalkoxymethyl-1,3-tniazolid-4-ones, but Et g-cyclohexylaminocrotonate (I) and iso-PrNHC-Me:CHCO2Et (II) with HSCH2CO2H (III) give the corresponding b-acetylthiotetronic acid amides. AcCH2CO2Et (59 g.), 32 g. HSCH2CO2Me, 150 cc. abs. EtOH, and 7.5 cc. abs. alc. HCl kept 3 days at room temp. and fractionated, the resulting MeO2CCH2SCMe. CHCO2Et (20 g.), b0.4 122-8°, treated immediately with 10 cc. concd. NH4OH, dild. with MeOH to soln., kept 2 days at room temp., and filtered yielded 4.1 g. H2ONO-CCH2SCMe: CHCO2Et (IV), m. 108° (aq. MeOH). III (0.4 mole) and 0.25 mole appropriate enamine in 250 cc. tech. CHCl3 refluxed 30-40 hrs. with the azeotropic removal of the H2O, cooled, washed with 5% NH4OH, dried, and evapd. gave 66% 2-methyl-2-carbethoxymethyl-4-thiazolidone (V), b0.06 132°, in. 55-6°. A series of similar runs with 0.5 mole III, 0.25 mole b-aminocrotonic acid Et ester and 250 cc. of various solvents was performed (solvent used, reaction time in hrs., and % yield of V given): iso-Pr2O + 1 cc. HCO2H, 24, 23; pure CHCl3, 24, 37; CCl4, 24, 10; C6H6, 24, 34; C6H6 + 1 g. p-MeC6H4SO3H, 31, 43; C6H6 + 1 cc. C5H5N, 31, 38; xylene, 24, 10. By the same method as V were prepd. the following compds. (% yield, b.p./mm., m.p., and nD20 given): 2-methyl-2-carbomethoxymethyl-4-thiazolidone, 30, 134°/0.1, --, 1.5207; 3-Me deriv. of V, 70, 121°/0.15, --, 1.5057; 3-PhCH2 deriv. of V, 57, 180°/0.2, --, 1.5538; 5-Me deriv. of V, 62, --, 63-4°, --; 2-methyl-2-(1'-methyl-1'-carbethoxymethyl)-4-thiazolidone (VI), 41, 151°/0.5, 65-6°, --; 1'-Pr analog of VI, 47, --, 77-9% --; 1'-PhCH2 analog of VI, 52, 190-2°/0-4,--,--; 2,2-dicarbethoxymethyl-4-thiazolidtme, 33, 174-5°/0.3, 50-1.5°, --; 2,2-(1'-carbethoxypentamethylene)-4-thiazolidone, 61, --, 89-90°, --. The appropriate a-mercaptocarboxylic acid (0.4 mole), 0.25 mole suitable b-oxocarboxylic acid esters, 31 g.
NH4OAc, and 250 cc. C6H6 refluxed 24 hrs. with the
azeotropic removal of H2O gave 30% 2-methyl-2-( (1',1
'-diethyl-1'-carbethoxymethyl)-4-thiazolidone, m. 93.5, 94°, and 48% 2-propyl-2-( 1'-ethyl-1'-carbethoxynlethyl)-4-thiazolidone,
b0.1. 147-8°, nd20 1.4991. V
(10 g.) and 10 cc. 30% aq. NaOH warmed with shaking to 30°, cooled immediately, washed with 10 cc. EtOAc, acidified with cooling
with 20% H2SO4, and extd. with EtOAc yielded 6.8 g.
2-methyl-2-carboxymethyl-4-thiazolidone, powder, m. 135.6°. V (20 g.), 150 cc. concd. NH4O H, and 250 cc. MeOH (satd. with NH3)
kept 24 hrs. at room temp. and concd. gave 2.4 g.
V (7.1 g.) in AcOH treated with 100 cc. 8% KMnO4 in portions, kept 2
hrs., decolorized with SO2, and refrigerated overnight yielded 6.1 g.
1,1-dioxide of V, m. 138-9°
(EtOH and C6H6). I (53 g.) and 37 g. III
in 250 cc. C6H6 refluxed 36 hrs. with 1 g. p-MeC6H4SO3H with the removal of 4
cc. H2O, washed with 5% NH4OH, and evap., gave 21 g. a-acetylthiotetronie acid cyclohexyl-amide (VII), m. 127° (EtOH). VII and
Sulfur heterocycles. VIII. Simple preparation of geminal dithiols and some further reactions. Jentzsch, Joachim; Fabian, Juergen; Mayer, Roland. Tech. Univ., Dresden, Germany. Ber. (1962), 1764-6.
cf. Angew. Chem. 74, 118 (1962); CA 57, 5877i. Cyclohexanone (I), cyclopentanone (II), and Me2CO treated in the presence of aliphatic amines with H2S gave the corresponding geminal dithiols in good yields. The dithiols were converted to 1,3-dithiolane-4,5diones, 1,3,5-trithianes, and 1,2,4,5-tetrathianes. I (51 g.) and 4.3 g. morpholine in 200 cc. MeOH, or EtOH, HCONMe2, Me2SO, treated with cooling 7 hrs. with H2S and acidified, and the oily product dried and distd. yielded 5961.5 g. cyclohexane-1,1-dithiol (III), b12 84°, n25D 1.5448. II (42 g.) and 4.3 g. morpholine gave similarly 48.3 g. cyclopentane-1,1-dithiol (IV), b10 63°, n25D 1.5469. Me2CO (29 g.) and 4.3 g. morpholine yielded l6-19 g. Me2C(SH)2 (V), b100 57°, m. 6-8°, n25D 1.5069. III (5.4 g.) in 150 cc. dry Et2O treated with shaking with 12.8 g. Na2CO3 and an equiv. amt. (C Cl)2 (VI), filtered after 4 hrs., and evapd. yielded 3.8 g. 2,2-pentamethylene-1,3-dithiolane-4,5-dione, m. 645° (hexane). IV (13.4 g.) and 12.7 g. VI gave similarly 4.7 g. 2,2-tetramethylene-l,3-dithiolane-4,5-dione, m. 33°. V (4.5 g.) and 6.4 g. VI yielded 4.2 g. 2,2-dimethyl-l,3-dithiolane-4,5-dione, m. 77-8°. III (14.8 g.) in 100 cc. C6H6 and 100 cc. H2O contg. CaCO3 treated dropwise during 3 hrs. with a satd. C6H6 soln. of 25 g. iodine at 50°, stirred 2 hrs., filtered, washed with aq. NaHSO3, and evapd. yielded 3.5 g. 3,3,6,6-bis(pentamethylene)-1,2,4,5-tetrathiane (VII), m. 131° (cyclohexane). IV gave similarly less than 10% 3,3,6,6-bis(tetramethylene) analog of VII, m. 153° (MeOH). V gave in the same manner about 5% 3,3,6,6-tetra-Me analog of VII, m. 95° (MeOH). III (7.4 g.) and 30 cc. concd. HCl refluxed 6 hrs. yielded 3.5 g. 2,2,4,4,6,6-tris(penta-methylene)-l,3,5-trithiane (VIII), m. 102° (C6H6 and then MeOH). IV (6.7 g.) yielded similarly 3.9 g. tris(tetra-methylene) analog of VIII, m. 98° (MeOH).
heterocycles. XIV. Synthesis of trithiones by the combined action of carbon
disulfide and sulfur on enamines. Fabian, J.; Gewald, K.; Mayer,
Roland. Tech. Univ.,
cf. preceding abstr. Enamines react with CS2 and S in polar solvents like HCONMe2 at room temp. to give trithiones. 1-Morpholino-1-cyclopentene gives in 50% yield 4,5-trimethylenetrithione (I), m. 123° and 1-morpholino-1-cyclohexene gives in 45% yield 4,5-tetramethylenetrithione (II), m. 101-2°.
Sulfur heterocycles. XXXI. Trithiones from enamines, carbon disulfide, and sulfur. Mayer, Roland; Wittig, Peter; Fabian, Juergen; Heitmueller, Renate. Tech. Univ., Dresden, Germany. Ber. (1964), 97(3), 654-60.
cf. preceding abstr. Enamines react smoothly in the cold with CS2 and S to yield trithiones; depending on the enamine type, mono- or 4,5-disubstituted trithiones were obtained in this manner. The appropriate enamine (0.2 mole) added dropwise to 6 g. S powder and 45.5 g. CS2 in 40 cc. HCONMe2 at 15° and stirred 2-4 hrs. at room temp. yielded the corresponding trithiones. In this manner were prepd. the following compds. (cor. m.p., appearance, % yield, and starting enamine given): I (n = 1) (II), 123° (sublimed), yellow-orange needles, 60, 1-morpholinocyclopentene [II.MeI, yellow needles, m. 152.0-3.5° (AcOEt)]; I (n = 2), 102° (sublimed), orange, 35, 1-morpholinocyclohexene; I (n = 3) (III), 98.5° (cyclohexane), yellow-orange needles, 50-5, 1-morpholinocycloheptene [III.MeI, m. 158° (AcOEt)]; IV, 122.5° (sublimed), orange-yellow needles, 6, 5-morpholino-1-thia-3-cyclohexene (b0.5110°, m. 32-5°); V, 126.5° (methylcyclohexane), red-orange leaflets, 45, 1-morpholino-1-phenylethene (b0.1 82-4°); VI (R = Et) (VII), 20°(b12 163°, red oil), 50, Et2NCH:CHEt [VII.MeI, nearly 100%, golden yellow leaflets, m. 160° (MeNO2)]; VI (R = Ph) (VIII),121-2°, red-orange leaflets, 30, 1-piperidino-2-phenylethene [VIII.MeI, nearly 100%, yellow needles, m. 172° (AcOEt)]. Cyclohexanone (24.5 g.) and 22.4 g. BuSH refluxed with p-MeC6H4SO3H with the azeotropic removal of the H2O yielded 19 g. 1-butylthiocyclohexene, b2.5 95°, n20D 1.5088. Cyclohexanone anil (34.6 g.) stirred 4 hrs. at 20° with CS2 and S yielded about 6 g. IX, pale yellow needles, m. 134°, and 17-20 g. unidentified yellow solid; IX.MeI, nearly 100%, pale yellow needles, m. 155-60°.
1,3-dithiole-2-thiones (isotrithiones). Mayer, Roland;
Gebhardt, B.; Fabian, J.; Mueller, A. K. Univ. Dresden,
The title compds. (1,3-dithiacyclopentene-2-thiones) (I) are formed from acetylenes in polar solvents with S in CS2 or from the Na acetylides with S in CS2 at room temp. The mercaptoacetylene derivs. from S and Na acetylides add CS2 in polar solvents at room temp. and cyclize by a nucleophilic attack of the sulfide-S of the trithiocarbonate group on the triple bond to give I in 50-70% yields. PhC.tplbond.CNa with S and CS2 in MeCN yielded 60% I (R = Ph). I (R = H) was obtained similarly or from C2H2 in 20% yield.
heterocycles. XXXII. Thin-layer chromatographic-spectroscopic investigations of
sulfur heterocyclic compounds. Mayer, R.; Rosmus, P.; Fabian, J.
cf. CA 60, 13237f; 61, 5525c. Rf values and ultraviolet spectra of 53 trithiones and 16 1,2-thiazoline-5-thione compds. are given. The thin layer chromatographic Rf values were obtained on 20 ´ 20-cm. glass plates covered with 250-m silica gel G layers, which had been dried 15 min. in air and activated at 120-30°. The samples are then applied and developed with 1:1 petr. ether-C6H6, CS2, or 3:1 C6H6-HOAc, and made visible by tetracyanoethylene. The solvent effect on the ultraviolet spectra is also discussed.
XXVII. Aliphatic Thioketones. Mayer, Roland; Morgenstern, J.;
Fabian, J.. Univ.
A review with 116 references.
spectra of saturated aliphatic thiones. Fabian, J.; Mayer,
R. Tech. Univ.,
The electronic absorption spectra of satd. aliphatic thiones were recorded in the region of 210-600 mm. In 4 cases, 2 intense peaks in the ultraviolet and 1 weak absorption in the visible region were found. Solvent effects and the absorption intensities were used for a preliminary assignment of the electronic transitions. The effect of enolization on the ultraviolet spectra of some more thiones is considered.
LCAO-MO. calculations for organic sulfur compounds. Fabian, J.; Mehlhorn, A.; Bormann, J.; Mayer, R. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (1965), 14(2), 285-91.
The Hueckel M.O. method is used for a rational math. derivation of quantum chem. factors from semiempirical Coulomb and resonance integrals. Thus, for CH2S, the total p energy (Ep) is 2.4054, transition energy (EN®V1) 1.8554 B, electron ds. (qs) 1.1425 and (qc) 0.7575, total mobile bond order (pcs) 0.9701, and superdelocalizabilities (ScS) 1.0331, (SnS) 1.1605, (StS) 1.0968, (ScC) 0.6298, (SnC) 1.9037, and (SrC) 1.2667. Values of Ep, EN®v1, q, and Hueckel nos. for the highest occupied and lowest free M.O.'s are calcd. for 48 aliphatic, aromatic, and heterocyclic S compds.
Nitrogen-free, geminal, aliphatic or cycloaliphatic dimercaptans. Fabian, Juergen; Jentzsch, Joachim; Mayer, Roland. (VEB Farbenfabrik Wolfen). (1964), 2 pp. DE 1173894 19640716 Patent language unavailable. Application: DE 19620924.
The title dimercaptans can be obtained in good yield from aliphatic or alicyclic ketones reacting under pressure with H2S with addn. of amines, provided the reaction itself is permitted to take place at atm. pressure, at 0°, in the presence of a polar org. solvent. Thus, into a soln. of 51 g. cyclohexanone and 4.3 g. morpholine in 200 ml. MeOH, H2S was conducted for 7 hrs. at 0°; the sepd. oil obtained after acidification of the soln. was dissolved in petroleum ether, dried, and distd. over Na2SO4 to give 1,1-dimercaptocyclohexane, 80-83%, b12 84°, n25D 1.5448. In a similar manner were prepd. 1,1-dimercaptocyclopentane, b10 63°, n25D 1.5469, 2,2-dimercaptopropane, b100 57°, f.p. 6-8°, n25D 1.5069, and 2,2-dimercaptobutane, b25 49°, f.p. .apprx.-25°, n25D 1.5072.
Quantum chemical investigation on the polarographic behavior of thiocarbonyl compounds. Mehlhorn, A.; Fabian, J.; Mayer, R. Tech. Univ., Dresden, Germany. Zeitschrift fuer Chemie (1965), 5(1), 21-2.
The polarographic half-wave potential of 20 thiocarbonyl compds. in 40% aq. iso-PrOH system with pH 7.2 phosphate buffer at 25° was measured. A linear correlation was observed between half-wave potential and Hueckel's no. of LFMO-energy.
Description of N ® V1 - transition of some S heterocycles with the Hueckel molecular orbital method. Fabian, J.; Mehlhorn, A.; Mayer, R. Tech. Univ., Dresden, Germany. Zeitschrift fuer Chemie (1965), 5(1), 22-3.
N ® V1 excitation energy and N ® V1 transition energy of 32 S-contg. compds., including trithione, isotrithione, 1,2-dithione, 1,3-dithione, thiophene, and thiopyrone- thione were calcd., and the wave no. of the absorption max. was detd. exptl. Generally, a satisfactory linear correlation was observed between the calcd. N ® V1 transition energy and wave no.; however, phenyl substituted S-heterocycles caused a shift to shorter wave nos.
Quantum chemical study of reactivity on four S-containing heterocycles. Mehlhorn, A.; Fabian, J.; Mayer, R. Tech. Univ., Dresden, Germany. Zeitschrift fuer Chemie (1965), 5 23-4.
Reactivity indexes of 4-phenyl-1,3-dithiol-2-one (I), 4-phenyl-1,3-dithiolium (II), 4-phenyl-1,2-dithiolium, and 5-phenyl-1,2dithiolium cation (III) were calcd. The p-electron d., superdelocalization probability, atom localization energy, and Z°factor for the position 2', 3', or 4' in the phenyl radical and for the position 4 or 5 in the 5-membered ring were given.
LCAO-MO calculations concerning sulfur-containing p-systems. V. Comparison of HMO- [Hueckel molecular orbitals] and HMO-SC [self consistent] calculations concerning thiocarbonyl compounds. Mehlhorn, A.; Fabian, J.. Tech. Univ. Dresden, Germany. Zeitschrift fuer Chemie (1965), 5(11), 420-1.
cf. CA 62, 11297b, 12753h, 16030h.
Inaccuracies introduced into simplified mol.-orbital calcns. by using
arbitrarily selected parameters may be minimized with the aid of the w-correction technique, (Streitwieser, Molecular Orbital Theory for
Organic Chemists, New York, John Wiley & Sons, 1961, 489 pp.). Accordingly, 12 combinations of the type
RR1C:S, R,R1.dbd.S, O, N, Cl, were examd. in 7 different models in order to
evaluate the influence of the resonance integral ksc on several quantum chem.
correlation factors, the change of these factors during the iteration process,
and the influence of the iteration parameter w. The statistical interpretation
of the confrontation of the quantum chem. data of all models are tabulated and
indicate the following trends: (1) A variation of ksc within the limits 0.6 and
0.9 exerts no influence on the accuracy of correlations between exptl. and
theoretical data; it affects only the comparison of the spectroscopical
absorption max. with EN®V1 transition energies. (2) The HMO-SC
method, which repeats the calcns. of the corrections until the matrix elements
become self consistent (
absorptions of 3H-1,2-dithiol-3-thiones (trithiones). Fabian,
Juergen; Mayer, Roland. Tech. Univ.,
Ir spectra of the following I in CCl4 soln. were detd., and assignments of the bands were made (R1 and R2 given): H, H; Me, H; n-C5H11, H; PhCH2, H; Ph, H; p-MeC6H4, H; p-BrC6H4, H; p-MeOC6H4, H; CO2Et, H; H, Me; H, Et; H, cyclohexyl; H, Ph; H, MeC6H4; Me, Me; (CH2)3; (CH2)4; (CH2)5; and CH: CHCH: CH.
1,2-Dithiacyclopentene-3-thiones. Fabian, Juergen; Gewald, Karl; Mayer,
Roland. (VEB Farbenfabrik Wolfen).
Enamines reacted with CS2 and S in polar solvents at room temp. to give the title compds. (I). Thus, 6.1 g. CS2 was added to a suspension of 0.64 g. S in 3.1 g. 1-morpholinocyclopentene and 4 ml. HCONMe2, the mixt. stirred 4 hrs. and poured into H2O, and the solid filtered off and extd. with isooctane to give 35-40% 4,5-trimethylene-1,2-dithiacyclopentene-3-thione [I, (RR1 = ) (CH2)3], m. 120-2°. Similarly prepd. were the following I (enamine, R, R1, % yield, and m.p. given): 1-morpholinocyclohexene, (RR1 = ) (CH2)4, 30-5, 101-2° (Me2CO); 1-morpholino-1-phenylethene, H, Ph, 45, 126° (methylcyclohexane); EtCH:CHNEt2, Et, H, 50, 20° (b12 163°). I are lubricant additives and intermediates in the manuf. of pharmaceuticals, inhibitors, pesticides, and disinfectants.
molecular orbital calculations on heterocyclic systems containing
sigma-bivalent sulfur. Zahradnik, R.; Fabian, J.; Mehlhorn, A.;
Kvasnicka, V. Ceskoslov. Akad. Ved,
Semiempirical mol. orbital calcns. are reported for thionaphthene, isothionaphthene, thialene, isothialene, and dibenzothiophene, and the theoretical values of the excitation energies and transition energies compared with those obtained by uv spectroscopy. The H.M.O. (Hueckel M.O.) and S.C.F. values of squared expansion coeffs. of the frontier mol. orbitals in positions bearing H atoms are compared for their potential significance in interpreting E.S.R. measurements. Also compared are the H.M.O. and S.C.F. mol. diagrams of the mols.
Roland; Hartmann, Horst; Fabian, Juergen; Mehlhorn, Achim. Tech. Univ.,
A review on the title compds. such as iso-p-electronic thiopyrylium salts (e.g., I), thiopyranthiones (e.g. II), thiopyranones (e.g. III), and methylenethiopyrans (e.g. IV), with 67 references.
Linear combination of atomic orbitals-molecular orbitals calculations in sulfur-containing p-systems. VI. Ultraviolet sulfur absorptions of 2H-1,3-dithiole-2-thiones. Fabian, Juergen; Fanghaenel, Egon. Tech. Univ., Dresden, Fed. Rep. Ger. Journal fuer Praktische Chemie (Leipzig) (1967), 36(5-6), 287-303.
The UV S absorption spectra of 36 2H-1,3-dithiole-2-thiones were measured at 215-500 mm in C6H12 and EtOH. The bands that can be used for the identification of this class of compds. and the effect of substituents on absorption are discussed. The longest wave length at which intense absorption takes place are compared with Hueckel M.O. indexes.
compounds. LXXXIII. Quantitative description of UV/Vis-absorptions
of simple thiocarbonyl compounds. Fabian, Juergen;Viola, H.; Mayer,
The long-wave band of aliphatic and aromatic thiocarbonyl compds. can be described empirically and quantum chem. by using statistical methods. From the absorptions of 60 compds. of the types XC(S)Y (X,Y = Me, CF3, CF2Cl, CN, Ph, CONH2, COOEt, CSNH2, Me, Ph, NH2, NHMe, NMe2, CONH2, COOEt, CSNH2, OMe, OPh, NH2, NHMe, NMe2, NHPh, NHCOMe, SMe, SCF3, SPh, F, Cl) between 250 and 650 mm absorption increments which specifically characterize the substituents are derived. The values calcd. by means of these increments are in good agreement with the exptl. results. For some aliphatic types (X,Y = NH2, NHCOMe, OMe, SMe, Cl) the values of the long-wave bands calcd. in this manner are compared with those obtained by quantum chem. Hueckel M.O.- self-consistent-calcns. following the Janssen procedure. Furthermore, the frequencies of the frequencies of the first intense absorptions are detd. quantum chem. for the last mentioned compds. The quantum chem. as well as the empirical methods permit spectral properties of compds. not as yet prepd. or spectroscopically investigated to be deduced. Thus, the first 2 spectral absorptions of MeC(S)Cl hitherto unknown are predicted. 27 references.
L.C.A.O.-M.O. calculations for sulfur-containing p systems. IX. Description of thiocarbonyl absorption bands with the simple H. M. O.-method. Fabian, Juergen; Mehlhorn, Achim. Tech. Univ., Dresden, Fed. Rep. Ger. Zeitschrift fuer Chemie (1967), 7(5), 192-4.
Lowest unoccupied M.O. of a series of thiocarbonyl
compds. were calcd. by the simple Hueckel M.O. method. A linear correlation was observed between the
n-p* transition absorption wave no. (~n) and Hueckel no. (XLFMO) (
the PPP method to interpreting the uv-visible spectra of sulfur containing p-electron
systems. I. Fabian, Juergen.
Fak. Math. Naturwiss., Inst. Organ. Chem.,
The organic p-electron systems in the uv and visible regions can be interpreted. The Pariser-Parr-Pople (PPP) method of calcg. the semi-empirical MO-LCAO in zero differential overlap provides an approxn., with consideration of the Coulomb repulsive integral, of Hueckel's MO theory. SCF-LCI-PPP calcn. of org. S compds. yields encouraging results.
orbitals-linear combination of atomic orbitals.
Calculations on sulfur-containing p electron systems.
XI. Electron structure of mercaptobenzene. Fabian, Juergen;
Mehlhorn, Achim; Troeger, Gudrun.
PhSH is treated as an 8-electron-system with seven basis orbitals according to a self-consistent field-configuration interaction-method in the Pariser-Parr-Pople approxn. All of the one-center repulsion integrals were assumed to be the same (gCC = gSS = 10.84 ev.) and the two-center repulsion integrals were detd. according to the Mataga-Nishimoto relation. Values of US = 21 ev. and bCS = 0.5 bCC were derived empirically from the uv-absorption spectrum of PhSH in the region 155-300 mm. The calcns. on PhSH and PhSMe, besides allowing an interpretation of the uv-spectra, give predictions of ionization properties and charge distributions showing good agreement with expt. The usefulness of the suggested parameters is shown with calcns. on 1,2-, 1,3-, and 1,4-dimercaptobenzene, 1- and 2-mercaptonaphthalene, and 9-mercaptoanthracene. 49 references.
calculations for thiofluorenone. Fabian, Juergen; Mehlhorn, Achim.
Tech. Univ. Dresden,
The assignment of the long-wave S absorption in thiofluorenone (I) was not in agreement with the observed solvent effect. The medium intensity band at 430 mm shifted to longer wavelength on change of solvent from cyclohexane to EtOH or MeCN, suggesting an n-p* transition. Extended spectral measurement in the longer wavelengths showed the presence of a new absorption band with characteristic neg. solvatochromy. Calcns. according to Janssen and Sandstroem (CA 62: 6003a) made evident a requirement for a CS band for I at around 650 mm. Pariser-Parr-Pople calcns. with repulsion integrals according to Mataga and Nishimoto (CA 52: 2536h) showed that the band at 430 mm was due to a weak p-p* transition. Results of ASHMO-LCI and SCF-LCI calcns. were tabulated and gave satisfactory agreement with exptl. detns. The agreement between exptl. and calcd. values of the p-dipole moment was less satisfactory. The discrepancy was attributed either to a faulty assessment of the s-moment of I or to a wrong comprehension of the model used for the p-moment. I was prepd. according to Brosowski and purified by the procedure of Campaigne and Reid. (CA 42: 3370a).
Organic sulfur compounds. XCI. Protonation of iso-p-electronic thiotropones. Bohnensack, R.; Fabian, Juergen; Mayer, Roland. Tech. Univ., Dresden, Fed. Rep. Ger. Journal fuer Praktische Chemie (Leipzig) (1968), 37(1-2), 41-6.
The protonation of several trihione, isotrithione, and a-dithiopyrone derivs., which are iso-p-electronic with the thiotropones, as well as the protonation of PhCS-SMe and of cyclic trithiocarbonates, were investigated in aq. H2SO4. The H0 semiprotonation values were detd. spectrophotometrically. The basicities were compared with the Hueckel M. O. electron ds. The basicities increased with the p-electron d. on the thiocarbonyl S.
spectroscopic studies on vinyl methyl sulfide. Fabian, Juergen; Kroeber, H.; Mayer, R.
Ir spectra of methyl vinyl sulfide (I) was studied at 400-3300 cm.-1 for vapor, liq., soln., and solid phases. The Raman spectrum and the polarization properties were also measured. A vibrational assignment is suggested. By measurement of the temp. dependence of ir absorption, I is shown to exist in 2 conformers. The s-cis-form is the more stable one.
Preparation and uv sulfur spectrum of diphenylcyclopropenethione. Laban, Gunter; Fabian, Juergen; Mayer, Roland. Tech. Univ., Dresden, Fed. Rep. Ger. Zeitschrift fuer Chemie (1968), 8(11), 414-15.
Treatment of diphenylcyclopropenone (I) with an equimolar amt. of P4S10 gave diphenylcyclopropenethione (II) and 4,5-diphenyl-1,2-dithiole-3-thione (III). II and III were obtained in approx. equal amts. from reaction of I and P4S10 at 45° for 1 hr. in C6H6, while in boiling C6H6 only III was formed. II was obtained in better yield from 3,3-dichloro-1,2-diphenylcyclopropene and AcSH. The by-product was 3,3-bis(acetylthio)-1,2-diphenylcyclopropene. The uv spectrum of II is discussed.
calculations on sulfur-containing heterocycles. Fabian, Juergen; Mehlhorn, Achim;
Zahradnik, Rudolf. Tech. Univ.,
The Pople-Pariser-Parr procedure (neglect of the penetration integrals, const. parameters, idealized geometry, p model for the S, and limited no. of singly excited-states in the configuration interaction) provides a satisfactory interpretation of the singlet-singlet absorptions of heterocyclic S-contg. compds. in the uv and visible spectral regions. The authors suggest the values; valence state ionization potential of S = 20 ev., bCS = 0.7bCC, where bCS is the core-resonance integral of the C-S bond, and gSS = gCC, where gSS is the monocentric electronic repulsion integral, as parameters for s-bivalent S and employ the Mataga-Nishimoto relation for the two-center repulsion integrals. A reliable evaluation of the calcd. charge distribution in the ground state would require addnl. exptl. data.
L.C.A.O.-M.O. calculations of sulfur-containing p-systems. XV. p-Electron structure of 2-dimethylamino-thiophene. Fabian, Juergen. Tech. Univ. Dresden, Dresden, Fed. Rep. Ger. Zeitschrift fuer Chemie (1968), 8(7), 274-5.
The p-electronic structure of 2-dimethylaminothiophene was investigated by calcg. the self-consistent field-orbitals and the spectral transitions of the compds. by using the wave functions for 4 monoexcited states in the mutual exchange. The calcd. transition energies and oscillator strengths of dimethylaminobenzene and 2-dimethylaminothiophene and the corresponding unsubstituted compds. are compared with the measured spectral curves; the spectral characteristics are in good agreement with the theory.
on sulfur-containing p-electron systems. XVI. Pariser-Parr-Pople calculations on
thiocarbonic acid derivatives as crossed conjugated systems. Fabian,
Juergen. Tech. Univ. Dresden,
Semiempirical selfconsistent field-configuration interaction calcns. were extended to derivs. of thiocarbonic acid to explain specific properties of intense near-uv absorptions. Good agreement with exptl. data was obtained although parameters were not adjusted. The change of electron distribution by optical excitation is more complicated than assumed for thiocarbonic acid as a crossed conjugated system.
calculations and comparison of electronic spectra of iso-p-electronic
oxygen, nitrogen, sulfur, and selenium heterocycles. Fabian, Juergen; Mehlhorn, Achim;
Zahradnik, Rudolf. Tech. Univ. Dresden,
Dresden, Fed. Rep.
Heterocyclic compds. (42) formally derived from alternant or nonalternant hydrocarbons by replacing a C:C group by an O, N, S, or Se atom, are studied by the Pariser-Parr-Pople-type of calcn. By means of these results the near uv and visible spectra are described. The S and the Se atoms are treated in the L.C.A.O.-M.O. method by using the p-model. In most cases spectral features are not only well reproduced, but interrelations of the spectra of iso-p-electronic compds., possessing analogous structures, are interpreted, too. On calcg. cationic N heterocycles by using parameters of pyrrol type N results are unsatisfactory.
calculations on sulfur-containing p-electron systems. XX. PPP [Pople-Pariser-Parr] calculations on the
mercaptotropylium ion and iso-p-electronic sulfur-heterocycles. Fabian,
Juergen; Fabian, K.; Hartmann, Horst. Tech. Univ. Dresden,
Iso-p-electronic thiotropones are converted by means of protonation into mercapto-substituted ions of the analogous heterocycles. These ions show various characteristic absorption max. in the uv region. Semiempirical self-consistent field-L.C.I. calcns. with parameters derived formerly reflect the exptl. results satisfactorily. By appropriate adjustment of the S parameter, Us, it is possible to est. the influence of Me substitution on the exocyclic S atom.
properties of 3-ethoxy-1,2-dithiolium salts. Faust, Juergen;
Fabian, J. Tech. Univ.
Freshly prepd. (Et3O)BF4 (19 g.) in 40 ml. dry CH2Cl2 was added to 0.1 mole I in dry CH2Cl2 and the mixt. kept several hrs. to give II, very sensitive to moisture but pure enough for most reactions. II were obtained anal. pure by crystn. from Ac2O with considerable loss. The tabulated II were prepd., and their uv spectra detd. in concd. H2SO4. Alcs. reacted with II to form I. To 0.93 g. finely divided II (R = H, R1 = Et) in 5 ml. pure Ac2O, 0.8 g. 70% HClO4 was added with stirring. On warming crystals of 3-ethoxy-5-phenyl-1,2-dithiolium perchlorate pptd. in a few min. This reaction may proceed explosively! The product was washed twice with 0.5 ml. Ac2O and then with dry, peroxide-free Et2O to obtain 0.46 g. of a product, decompg. 81-113°, or on standing for a few months.
calculations of sulfur-containing p-systems. VIII.
UV/Vis absorptions of arenedithiocarboxylic acid esters. Fabian, Juergen; Scheithauer, Steffen;
Mayer, Roland. Tech. Univ., Dresden, Fed. Rep. Ger. Journal
fuer Praktische Chemie (
The uv absorption spectra were recorded for some arenedithiocarboxylic acid esters in cyclohexane, EtOH, and MeCN. Absorption max. and solvent shifts were detd. and are tabulated. A simple Hueckel L.C.A.O.-M.O. treatment permits a description of the excitation energies of the longest-wave absorption bands of heterocyclic S compds. in the uv and visible spectral regions. The effect of substituent on the n-p* and p-p* transitions are discussed. Spectroscopic substituent consts. were detd. from the s-absorption max. near 300 nm. of the esters substituted with electron donors in the para position. Linear correlation was found between these spectroscopic substitution consts. and those found for other series (literature), the Hammett sp, and substitution consts. calcd. from free energies.
calculations on sulfur-containing systems.
XVIII. UV/Vis absorptions of
2H-thiopyran-2-thiones. Fabian, Juergen; Laban, Gunter. Tech. Univ. Dresden,
The electronic absorption spectra of 17 2H-thiopyran-2-thiones have been recorded in the region of 220-500 mm. Characteristic absorption were found. The spectra of 2H-thiopyran-2-thione (I) and of the isomeric 4H-thiopyran-4 thione have been calcd. by a simple self-consistent field, configuration interaction, Pople, Pariser, and Parr method, taking into account 9 singlet monoexcited configurations. Excellent agreement with the exptl. dates of the intense bands were obtained with parameters formerly derived from S-heterocycles and thioketones. The calcns. were extended to some derivs. of I.
M.O.-L.C.A.O. calculations of sulfur-containing p-electron systems. XIX. P.P.P.[Pariser-Parr-Pople] and M.I.M. [molecules-in-molecules] calculations of thiophenols, phenols, and anilines. Hartmann, Horst; Fabian, Juergen. Tech. Univ. Dresden, Dresden, , Ger. Dem. Rep. . Ger. Berichte der Bunsen-Gesellschaft (1969), 73(1), 107-10.
The p-electron properties of some monosubstituted benzenes have been calcd. by means of the P.P.P. and the M.I.M. method by using a uniform set of parameters. The comparison of the results shows that both methods yield similarly satisfactory results only with thiophenol and thioanisole, whereas with compds. contg. strongly coupling substituents only the P.P.P. method is useful.
L.C.A.O.-M.O. calculations of sulfur-containing p-systems. XXI. Thienothiapyrylium ions as new 10-p-electron systems. Fabian, Juergen; Hartmann, Horst. Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Tetrahedron Letters (1969), (4), 239-42.
An equimolar mixt. of AcCH2COMe and 2-mercaptothiophene in Ac2O treated dropwise with HClO4 and the mixt. dild. with Et2O yielded 85% 2,4-dimethylthieno[2,3-b]-thiopyrylium perchlorate (I), m. 120-3°. Similarly were prepd. 2,4-dimethylthieno[3,2-b]thiopyrylium perchlorate (II), m. 163-5°; 2,4-dimethylthionaphtheno[2,3-b]thiopyrylium perchlorate (III), m. 233-8° (decompn.); and 2,4-dimethylthionaphtheno-[3,2-b]thiopyrylium perchlorate (IV), m. 222-5°, in 90, 70, and 80% yields, resp. Analyses and uv absorption spectra are given for all compds. Attempts to form the parent compds. by analogous reaction with EtOCH:CHCH(OEt)2 were unsuccessful though reaction with 2-mercaptothiophene gave a small amt. of 1,3-bis(a-thienylthio)trimethinium perchlorate (V), m. 137-9°. The preparative studies were made in connection with theoretical studies on the S-contg. 10-p systems. Semiempirical self consistent field (SCF)-LCI calcns. led to evidence as to the spectral absorption of this type of compds. and it appeared that the neutral 10-p-systems distinguished by differing mol. symmetry, benzo[b]thiophene, thieno[2,3-b]thiophene, thieno[3,2-b]thiophene, and thieno[3,4-b]thiophene should show differing spectra, whereas the isomeric thieno[b]thiopyrylium ions, as well as the thieno[b]tropylium ion should possess a far-going similar absorption characteristic. The spectral curves of the cationic system agreed with the expectation. The thiopyrylium character of these ions underlined the p-electron distribution obtained by SCF calcn. and detailed in mol. diagrams.
L.C.A.O.-M.O. calculations of sulfur-containing p-systems. XXII. Calculation of [the position of]color[determining bands] of thioformaldehyde. Fabian, Juergen; Mehlhorn, Achim. Tech. Univ. Dresden, Dresden, , Ger. Dem. Rep. Ger. Zeitschrift fuer Chemie (1969), 9(7), 271-2.
Energies of the singlet ® singlet and singlet ® triplet n-p* transitions in thioformaldehyde were calcd. as 531 and 657 nm., resp., by using a Pariser-Parr-Pople calcn. previously described by the authors (1967), and by using exptl. ionization potentials reported by A. Jones (1967). Similarly calcd. values for the corresponding transitions in formaldehyde agreed well with exptl. data.
L.C.A.O.-M.O. calculations of sulfur-containing p systems. XXIII. p-Electron structure of naphthothiopyrans. Fabian, Juergen. Tech. Univ. Dresden, Dresden, , Ger. Dem. Rep.. Ger. Zeitschrift fuer Chemie (1969), 9(7), 272-3.
p-Electron structure of naphthothiopyrans is discussed. Results of semiempirical selfconsistent field-linear configuration interaction calcns. of electron structure of these compds. without explicitly including d-state contributions are compared with literature exptl. data. The conclusion that the d-states contribute strongly to electron distribution in these compds. is premature. The p-model satisfactorily explains reactivity of the a,a'-position in these compds. as well as electronic transition energies.
Quantum chemical calculations of the structure of 1,2-dithiin. Borsdorf, Rolf; Hofmann, H. J.; Koehler, H. J.; Scholz, M.; Fabian, J.. Sekt. Chem., Karl-Marx-Univ., Leipzig, , Ger. Dem. Rep. Ger. Tetrahedron (1970), 26(13), 3227-31.
Quantum chem. calcns. confirm the proposed heterocyclic structure of 1,2-dithiin. The Pariser-Pople-Parr method allows the interpretation of the color of this compd. Extended Hueckel theory calcns. point out the pos. gross population of the S-S bond.
Semiempirical Pariser-Parr-Pople calcns. were used to predict singlet-singlet electronic transition energies, oscillator strengths and transition polarizations for 33 compds. and their anions. Generally, calcd. and exptl. data agreed.
hydrocarbons according to the Pariser-Parr-Pople method with accounting for the
iterative correction of integrals for adjacent atoms. Fabian, Juergen; Troeger, G. Sect. Chem.,
Tech. Univ., Dresden, , Ger. Dem. Rep.
The spectral properties of the alternant and nonalternant hydrocarbons of the mono- and bi-cyclic systems were calcd. using the method described earlier (R. Parr, 1964). Good agreement was found between the theoretical and exptl. data. The ionization potentials and bond lengths were calcd. and tabulated.
[PPP] calculations on hydrocarbons with a self-consistence correction for the
adjoining integral. II.
Nonalternating, polycyclic hydrocarbons. Troeger, G.; Fabian, J. Sekt. Chem., Tech.
Univ. Dresden, Dresden, Ger. Dem. Rep.
Zeitschrift fuer Physikalische Chemie (
The nonalternating hydrocarbons cyclopenta[ef]heptalene (aceheptylene), cyclohepta[de]naphthalene (pleiadene), cyclopenta[de]naphthalene (acenaphthylene), benz[a]azulene (1,2-benzazulene), benz[f]azulene (5,6-benzazulene), azuleno[5,6,7-cd]phenalene, and pentaleno[2,1,6-def]heptalene were calcd. by a LCAO-MO-SCF-PPP method, by using an iterative correction of the neighboring resonance integrals bmn and interaction integrals gmn. By using a limited configuration-interaction, the absorptions in the uv and in the visible range can be well interpreted. Contrary to earlier studied p-electron systems, the linear relation between p-order of bond and bond distance is badly fulfilled.
Studies of furfural
and its derivatives by quantum mechanical methods.
In this abstr. LCI is limited configuration interaction. SCF-LCI (g integral calcd. by Mataga-Nishimoto approxn.) calcns. of low-energy transitions are in good agreement with those obtained by the HMO-LCI method for arenecarboxaldehydes. 1-Azulenecarboxaldehyde is the exception. The other aldehydes studied are PhCHO, 1-C10H7CHO, 2-C10H7CHO, 9-formylphenanthrene, and 9-anthracenecarboxaldehyde. Transitions are also calcd. for furfural.
calculations on sulfur-containing p-electron systems. XXVI.
Physicochemical properties of alkyl-substituted dithiolium salts. Fabian,
K.; Hartmann, H.; Fabian, J.; Mayer, R. Sekt. Chem., Tech. Univ. Dresden,
The effect of alkyl groups on the uv spectrum, the charge-transfer spectrum with I-as donor and the polarog. properties of 1,2-and 1,3-dithiolium cations has been studied and compared with the results of SCFLCI (linear configuration interaction) calcns. The chem. shifts of the ring and Me protons detd. by NMR spectroscopy were correlated with the p charges calcd. for both cations. The nonuniform charge distribution of dithiolium cations is confirmed by NMR data. Due to the electrondonating properties of alkyl groups the p-electron d. of the heterocyclic ring increases. This results in the decrease of the electron affinity of the cations. This effect is the higher, the more pos. the position is to which the alkyl groups are bound. The substituent effect on the uv spectra, however, is not detd. by the mol. electron distribution in the ground state.
calculations on sulfur-containing p-electron systems. 27.
Ultraviolet-visible absorption spectra of thioaldehydes and thioketones. Fabian, Juergen. Sekt. Chem., Tech. Univ.
Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Physikalische Chemie (
MO calcns. were made on conjugated thioaldehydes and thioketones by the Pariser-Parr-Pople (PPP) method to explain their absorption behavior in the uv and visible range. Based on CNDO (complete neglect of differential overlap)/2 calcns. on HCSH, the s-charge distribution and the dp states of S can be neglected. In addn. to p ® p* transitions the color-detg. n ® p* transitions were studied by taking into account the wave functions of the lone electron pair which is approx. located on S. The theoretical results agreed with the exptl. data.
LCAO-MO calculations of sulfur-containing p-systems. 28. p-Electron structure of dithiolo[4,3-b]pyrrol-5(4H)-ones. Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1972), 12(9), 348-9.
The p-electron structure of the yellow cryst. antibiotics I, II, III, IV, V, VI and the model compd. VII were investigated by a PPP approxn. with neglecting the Me group influence in the 4 planar conformations (obtained by rotation around the exocyclic C-N bonds). The 3 characteristic absorption bands in the calcd. spectra were explained by four p ® p transitions. The amino group in I, II, III, IV, V, and VI had an auxochromic effect.
LCAO-MO calculations of sulfur-containing p-systems. 29. Protonation of bisdithiolomonomethines. Fabian, Juergen; Hartmann, Horst. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1972), 12(9), 349-51.
The intensively colored solns. of the methines I [R, R4 = H or Ph; R1 = H or Me; R2 = H, Ph, COPh, or CO2Et; R3 = H; RR1 = benzo; R2R3 = CH2CH2 or (CH2)3] and II (R, R3 = Ph; R1, R2 = H; or RR1 or R2R3 = 1-cyclohexen-1,2-ylene) in org. solvents absorbed light of 520-630 nm, while solns. of I and II in mineral acids remained colorless due to protonation. A comparison of the uv and visible spectra of I and II with those of III and IV indicated that the protonation of I and II proceeded in the meso-position to give the derivs. V and VI, resp. V and VI absorbed more intensely and at higher wavelengths than I and II owing to the interannular, nonbonding S-S interactions, as confirmed by p-MO PPP calcns.
of sulfur compounds. Fabian,
Juergen. Chem. Dep., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep.
Editor(s): Senning, Alexander. Sulfur Org. Inorg. Chem. (1972), 3 39-90.
The topics reviewed with 363 refs. include: approxns. used in the calcns., MO-LCAO methods, valence properties of S, electronic structure of S compds., and calcn. of properties (mol. structure, heats of formation, polarity, ionization, spectra, chem. reactivity).
Quantum chemical studies of furfurole and derivatives. 2. CNDO [complete neglect of differential overlap]/2 calculations of the conformational isomerism of furfurole. Fabian, Juergen; Mehlhorn, Achim; Perez, Carlos. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1973), 13(3), 116-18.
The bond lengths, angles, and orders, electron energies, charge ds., rotational barrier, and dipole moment were detd. for the s-cis and s-trans rotamers of furfural by CNDO/2 calcns. Good agreement with exptl. data was obtained.
LCAO-MO calculations on sulfur containing p-systems. XXX. Tautomerism of monothioacetylacetone. Fabian, J. Sekt. Chem. Tech., Univ. Dresden, Dresden, Ger. Dem. Rep. Tetrahedron (1973), 29(16), 2449-56.
UV spectroscopy and MO calcns. showed that MeCOCH2CSMe exists as an enolenethiol tautomeric mixt. in soln., the enethiol proportion increasing with temp. and solvent polarity.
MO-LCAO calculations of sulfur-containing p-electron systems. XXXI. Theoretical study of mesoionic sulfur heterocycles. Fabian, J.. Sekt. Chem., Tech. Univ. Dresden, Dresden, Fed. Rep. Ger. Journal fuer Praktische Chemie (Leipzig) (1973), 315(4), 690-700.
The electronic structure of the mesoionic 1,2-dithiol-4-one (I), II, and 3-thiopyrone and 4 isomeric iso-p-electronic compds. were calcd. by semiempirical MO-LCAO methods (PPP, Hartree-Fock, CNDO/2). The calcd. uv absorptions for Ph derivs. of I and II agreed with exptl. data.
Polymethine dyes with terminal S-heterocyclic groups had anomalous chromophoric properties. The vinylene shift of the first 2 homologs was often larger or smaller than the shift between higher members of the series. Absorption wavelengths of nonsym. dyes with S-contg. groups calcd. by the mean value rule differed from exptl. The deviation was caused by interannular no-bond S,S-interaction in the monomethine ion. A simple perturbational MO method based on the sym. properties of polymethine MOs reproduced the effects of pp-type overlap between AOs of adjacent S atoms at long wavelength absorptions. The S,S-interaction gave hypsochromic shifts in monomethines with (4n+2) p electrons (n = 1,2.....) and bathochromic shifts in monomethines with 4n p electrons.
The long-wavelength absorptions of ionic S-contg. polymethine dyes were detd. and discussed using the concepts of iso-p-electron count and color-detg. factors in polymethine chains. The limits of both concepts were indicated and the relations between color and constitution interpreted by quantum chem. p-methods.
LCAO-MO calculations of sulfur-containing p-electron systems. 32. Effect of nonbonded S---S interactions on the electron excitation spectra of a-(1,2-dithiol-3-ylidene) thioketones. Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1973), 13(1), 26-7.
The title spectra of the dithioles I, II, III (X = O or S, n O or 1) were calcd. by HMO limited configuration interaction and CNDO/i methods and compared with previous exptl. and calcd. data. The nonbonded O...S were smaller than the nonbonded S...S interactions.
procedure for determining chromophore structure. Fabian, Juergen; Keiper, Herbert. Sekt.
Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep.
Wissenschaftliche Zeitschrift der Technischen Universitaet
The MO calcns. of the electronic spectra of 52 compds. using localized and delocalized MO con-figuration interaction methods were compared with 4 calcns. by HMO and SCF methods and with exptl. data. The application to S-contg. compds. was discussed. The program used in these calcns. URAL 14, was described also.
calculations of the acichromism of aromatic azo compounds. Fabian, J.; Suehnel, J. Sekt. Chem., Tech.
Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Praktische Chemie (
All valence electron CNDO/2 and PPP calcns. were performed for RN:NR (I, R = H, Me, Ph, or substituted phenyl). The pH dependent acichromism obsd. for arom. I in strong mineral acids was explained by a protonation at one N atom inducing a characteristic change in the electron distribution.
MO-LCAO calculations of (N+-1) p-polymethines. Fabian, Juergen; Hartmann, Horst. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep., Zeitschrift fuer Chemie (1973), 13(7), 261-3.
The p-stabilization energies were calcd. for C1-13 (n ± 1) p-polymethines as well as p-charge order, p-superdelocalizability, and HMO transition energy data for the mono- and undecamethine structure.
Electronic structure and transitions of 1,2,3-trimethoxyacridine. Vlassa, M.; Ionescu, Maria; Fabian, J.. Inst. Chem., Cluj, Rom. Revue Roumaine de Chimie (1973), 18(1), 99-109.
The reactivity indexes (p-electron d., p-bond order, free valence index, superdelocalizability index), the bond lengths and the electronic transition (singlet-singlet, singlet-triplet and triplet-triplet) of acridine and 1,2,3-trimethoxyacridine were computed by an SCF-limited configuration interaction method. The calcd. electronic energies agree well with exptl. data.
Technical Studies in Chemistry, Textbook 1: Structure and Bonding-Atoms and Molecules. (Fachstudium Chemie, Lehrbuch 1: Struktur und Bindung-Atome und Molekuele) Grossmann, Gisbert; Fabian, Juergen; et al. Fed. Rep. Ger. (1973), 232 pp. Publisher: (Verlag Chemie, Weinheim, Ger.) Book written in German.
Acichromism of cyclic azo compounds. Suehnel, Juergen; Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1974), 14(7), 275-6.
Electronic structure calcns. of pyridazine, phthalazine, cinnoline, benzo[c]cinnoline, and their protonated forms are discussed. The changes in p electron d. and acidity on protonation and theS0 ® S1 (p p*) excitation are discussed in terms of acichromism.
Electronic spectrum of 1,2,3-trimethoxyacridine N-oxide. Vlassa, M.; Ionescu, Maria; Fabian, J.. Inst. Chem., Cluj, Rom. Revue Roumaine de Chimie (1974), 19(4), 665-9.
The SCF-MO-configuration interaction calcn. of the p-electronic transitions of 1,2,3-trimethoxyacridine N-oxide and its 9-Cl deriv. agreed with the exptl. data. The N-O group stabilized the transitions along the short axis of the acridine moiety while the MeO group stabilized transitions along the long and short axis of the acridine moiety.
Chain chromophores of polymethine dyes. Fabian, J.; Hartmann, H. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Signalaufzeichnungsmaterialien (1974), 2(6), 457-60.
The MO calcn. of orbitals of NH2+:CH(CH:CH)nNH2, NH2+:CH(CH:CH)nCH:BH2-, and BH2-:CH(CH:CH)nBH2 distinguished them as 3 classes. The relation of the dependence of the uv of these compds. on n with that of the polyenes and polymethines was discussed. The parameterization of the wave functions was also discussed.
calculations of polymethines.
Idealized polymethines are defined as conjugated chain mols. with complete bond equilization and charge alternation. A const. p-bond order along the chain with N atoms was derived for 3 types of polymethines which differ by the nature of the heteroat. end groups. Corresponding to the no. of p-electrons they are termined (N + 1)p, Np- or (N - 1) p-polymethines. This classification embraces closed shell as well as open shell systems. The relations for the energy eigenvalues, coeffs. and derived quantities have been obtained in closed form. The results for the different classes of polymethines are strongly related. Their mol. properties should be similar.
MO-LCAO calculations on polymethines. II. p-Electronic structure of polymethines. Fabian, Juergen; Hartmann, Horst. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal of Molecular Structure (1975), 27(1), 67-78.
The MO-theoretical characteristics of the (N-1)p, Np, and (N + 1)p polymethines are strongly related, and the eigenvalues can be derived by a mnemonic technique. The theoretical results establish the particular position of the polymethines among the p-systems and allow a rationalization of exptl. findings within the framework of the one-electron theory.
Band structure of linear polyacenes. Tyutyulkov, N. N.; Polansky, O. E.; Fabian, J. Inst. Strahlenchem., Max-Planck-Inst. Kohlenforsch., Muelheim, Fed. Rep. Ger. Zeitschrift fuer Naturforschung, Teil A: Astrophysik, Physik und Physikalische Chemie (1975), 30A(10), 1308-10.
For infinite polyacenes the energy gap (DE¥) is given by DE = (D2corr + D2geom)1/2, where Dcorr is a factor detd. by the electronic correlation and Dgeom is a molecular geometry dependent factor. We find in the selected case Dcorr>Dgeom. The energy gap values calcd. with this formula agree with the values calcd. from the spectroscopic data of polyacenes (0.8-0.9 eV).
Solvolysis of thiocarboxylic acid chlorides. Mayer, Roland; Schoenfeld, Peter; Viola, Horst; Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1975), 15(11), 443-5.
First-order rate consts. for the methanolysis of RCSCl (I; R = MeO, MeS, Me2N) were detd. at 15, 20, and 25° via conductometric data. A bimolecular mechanism was proposed for I (R = MeO, MeS) and an SN1 mechanism was proposed for I (R = Me2N).
Studies on the stability of oxocarbenium and thioxocarbenium ions. Mayer, Roland; Schoenfeld, Peter; Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1975), 15(12), 484-5.
Appearance potentials for [X-C:O]+ and [X-C:S]+ (I and II; X = MeO, MeS, Me2N) were detd. via mass spectral data. Dissocn. energies and stabilization energies for I and II (X = H, Me, Ph, OH, SH, NH2) were detd. via CNDO/2 formalism.
MO-LCAO calculations for sulfur-containing p-electron systems. XXXVI. Absorption and fluorescence measurements for phenyl-substituted pyrylium, thiopyrylium, oxathiolium, and dithiolium salts. Mayer, Roland; Suehnel, Juergen; Hartmann, Horst; Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Physikalische Chemie (Leipzig) (1975), 256(5), 792-800.
The uv absorption and fluorescence spectra of phenyl-substituted pyrylium, thiopyrylium, dithiolium, and oxathiolium salts in CH2Cl2 soln. were measured and the fluorescence quantum output in ref. to quinine sulfate was detd. The fluorescence arose from the energy-poor pp*-singlet state, whereby the O-contg. compds. inclined more strongly toward fluorescence than isologous S compds. The absorption behavior was satisfactorily interpreted by Pariser-Parr-Pople calcns. and the intensive long-wave-length absorption interpreted by a mol.-in-mol. model showed a strong charge-transfer character.
of organosulfur and organoselenium compounds. Fabian, J.. Sekt. Chem., Tech. Univ.
Dresden, Dresden, Ger. Dem. Rep. Organic
A review stressing quantum chemistry of cyclic conjugated compds. with 243 refs.
Energy spectrum of a,w-disubstituted polymethine chains. I. a,w-Substituted polyenes containing an even number of methine groups. Tyutyulkov, N.; Petkov, I.; Polansky, O. E.; Fabian, J. Inst. Org. Chem., Sofia, Bulg. Theoretica Chimica Acta (1975), 38(1), 1-8.
The change in the gap between the highest filled and lowest unfilled MO for the a, w-disubstituted polyenes X-(CH2)n-X with (2n + 2)p - electrons were calcd. as a function of n for n ® ¥ using an alternant MO method which took electron correlation into account. The gap was unaffected by substitution, as compared to the unsubstituted polyenes, which agreed with the exptl. p ® p* transitions of unsubstituted polyenes and polyenediones. The effect of bond alternation was small.
Educational Aids in Chemistry, Vol. 1: Structure and Bonding, Atoms and Molecules. 2nd Ed. (Lehrwerk Chemie, Bd. 1: Struktur und Bindung, Atome und Molekuele) Grossman, Gisbert; Fabian, Juergen; Kammer, Hans W. Ger. Dem. Rep. (1975), 236 pp. Publisher: (Deut. Verlag Grundstoffind., Leipzig, E. Ger.) M 25. Book written in German.
MO-LCAO-calculations on polymethines. III. Stability and reactivity. Fabian, J.; Hartmann, H.; Tyutyulkov, N. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Signalaufzeichnungsmaterialien (1976), 4(2), 101-14.
The stability and reactivity of polymethines were studied by quantum chem. indexes detd. via HMO formalism. According to Dewar's resonance energy, the polymethines should be energetically favored compared to the corresponding polyenic structures. The resonance energy per bond decreases with increasing chain length whereas the reactivity as reflected by the frontier orbital energies and reactivity indexes increases in the same direction.
calculations on polymethines. IV. Contribution to Daehne's concept of coupled
J.; Troeger-Naake, G. Sekt. Chem. Tech., Univ. Dresden, Dresden, Ger. Dem. Rep.
Journal fuer Praktische Chemie (
A quantum-chem. characterization of the polymethine p-electron system covered in previous papers by J. Fabian, et al. (1975-6) was extended to twisted polymethine substructures in more complicated mol. entities. The electronic structures of the composite systems were related to those of their components by subjecting the electronic wave functions to configuration anal. The localizability of the at. or mol. substructures was evaluated by the use of indexes which consider many of the structures as being composed of polymethinic, polymeric, and arom. fragments; however, the results clearly indicate serious errors in the application of this approach to several cyclic systems. Fortunately, the scope and limitation of this model can easily be recognized by application of the simple 2nd-order perturbation theory.
MO-LCAO calculations on sulfur-containing p-electron systems. Part XXXVII. CNDO/2-calculations on the stabilization of carbanions by s-bivalent sulfur. Fabian, J.; Schoenfeld, P.; Mayer, R. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Phosphorus and Sulfur and the Related Elements (1976), 2(1-2-3), 151-3.
The significantly enhanced acidity of C-H bonds attached to a s-bivalent S atom can be explained without taking into account the octet expansion of S. The higher-carbanion stabilization effect of S in comparison to O is related to the greater capability of the s-bivalent S to take up excess charge into the sp valence shell.
MO-LCAO-calculations on sulfur-containing p-electron systems. Part XXXVIII. CNDO/2-calculations on the stabilization of carbocations by s-bivalent sulfur. Mayer, R.; Fabian, J.; Schoenfeld, P. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Phosphorus and Sulfur and the Related Elements (1976), 2(1-2-3), 147-9.
From appearance-potential measurements, groups with s-bivalent S exert an unusual carbocation stabilization effect. The 3d orbitals of S are invoked to rationalize this effect.
MO-LCAO calculations on polymethines. 6. PPP calculations on the vinylene shift of symmetric dyes. Dedicated to Professor Walter Koenig on the 50th anniversary of the Koenig color theory. Fabian, Juergen; Zahradnik, Rudolf. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (1977), 26(2), 315-23.
Exptl. UV spectral data for polyene and polymethine dyes were in agreement with values calcd. via various PPP formalisms.
MO-LCAO calculations on sulfur-containing p-electron systems. Part XXXIX. On the electronic structure of diphenylsulfodiimide. Fabian, J.; Mayer, R. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Phosphorus and Sulfur and the Related Elements (1977), 3(2), 179-84.
PhN:S:NPh absorbs at considerably longer wavelengths (UV) than the isomeric PhSN:NPh. With the semi-empirical PPP method, an explanation is achieved without taking into account the d-orbital expansion of S. Mols.-in-mol.-type calcns. reveal the significance of the mixing of the locally excited configurations of the heteroat. groups with charge-transfer congifurations. For comparison the spectral data of PhN:S:NH and PhNSO are discussed.
calculations on sulfur-containing p-electron systems. 40. Configuration
analysis of the state functions of an intersecting conjugated bonding system. Fabian, Juergen. Sekt. Chem., Tech. Univ.
Dresden, Dresden, Ger. Dem. Rep.
Zeitschrift fuer Physikalische Chemie (
A configuration anal. for the description of the electronic states of S-Me dithiocarbamates, based on PPP and MIM models, is described.
MO-LCAO-calculations on polymethines. V. PPP-type calculations and configuration analyses of simple prototype dyes in terms of molecular subsystems. Fabian, J.; Troeger-Naake, G. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. International Journal of Quantum Chemistry (1977), 11(2), 259-69.
In order to elucidate certain controversies in interpreting the p-electronic structure of simple quinone and indigo dyes the Pariser-Parr-Pople SCb,g-wave functions were subjected to configuration anal. Whereas 2,5-diaminoquinone [1521-06-8] can be represented by coupling two trimethine-merocyanine chains, the analogous consideration is less appropriate for bispyrrolindigo [16292-04-9]. In this case the results of configuration anal. clearly indicate the limited applicability of the Longuet/Higgins-Murrell method.
Quantum chemical studies on furfural and derivatives. 3. The light absorption and acichromism of vinyl furfurals. Fabian, Juergen; Montero, Luis. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1977), 17(7), 266-7.
UV data for I, II, and III (n = 0-6) agreed with data calcd. via PPP-MO formalism. A red shift, obsd. for I in acid solns., was rationalized in terms of the polymethine character of the p-electron structure of the protonated compds.
Band structure of
even polyenes and ions of odd polyenes. Tyutyulkov, N.;
Singlet transitions (DEn) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains DE¥(I)/DE¥(II)=DE(I)/DE¥(III)=2:1. The energy gap is equal for the three systems. In cases II and III there is a level (NBMO) in the gap which vacant in II and occupied in III; the first optical transition in II and III depends on the semiwidth of the gap.
photochemistry in indigoid compounds.
II. Theoretical studies on the
base chromophore of trans- and cis-thioindigo. Suehnel, Juergen; Gustav, Klaus; Paetzold,
Roland; Fabian, Juergen. Sekt. Chem., Friedrich-Schiller-Univ., Jena, Ger. Dem.
Rep. Zeitschrift fuer Physikalische Chemie (
The photoinduced trans®cis isomerization of thioindigo compds. causes a hypsochromic shift of the long wavelength UV band. PPP-CI calcns. on the basis chromophore of thioindigo indicate that thio effect is due, predominantly, to the different non-bonded S...O interactions in the trans and cis isomers. A twisting of the central C:C bond leads to a bathochromic shift of the long wavelength UV band.
MO-LCAO calculations on sulfur-containing p-electron systems. 42. Comparative study of the applicability of the LHM [Longuet-Higgins-Murrell] method and PPP configuration analysis to the interpretation of substituent effects in p-electron systems. Fabian, Juergen; Troeger-Naake, Gudrun. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (1978), 27(3-4), 677-83.
The results of PPP-CA and LHM calcns. give excellent support to spectral interpretation methods which utilize unit system models. These models can be applied effectively to weakly coupled systems with a sufficient no. of configurations.
LCAO-MO calculations on sulfur-containing p-systems. 43. Sulfur heterocycles as coupled p-electron systems. Fabian, Juergen; Hartmann, Horst. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1978), 18(4), 145-6.
Frontier (HOMO-LUMO) orbital-interaction diagrams were shown for cyclic sulfides and disulfides (e.g., I and II). PPP calcns. indicate that the ground state of III is described better by the no-bond configuration than the ground state of I.
Negative acichromism of azo compounds. Suehnel, Juergen; Hartmann, Horst; Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1978), 18(5), 183-4.
Shifts in the long-wavelength p-p* transition of arom. azo compds. on protonation are ascribed to changes in the charge d. at the azo group.
Benzoquinone chromophores. Fabian, Juergen; Mehlhorn, Achim. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1978), 18(9), 338-9.
UV spectral data for o- and p-benzoquinone are in satisfactory agreement with PPP and INDO/S calcns.
color of organic azo compounds. Fabian,
Juergen. Sekt. Chem., Tech. Univ.
A review with 61 refs. in which the relation of MO to color is discussed.
calculations on polymethines. IX. The chromaticity of coupled oxonol and
cyanine dyes. Fabian,
J.. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep.
Journal fuer Praktische Chemie (
Streptopolymethines display low-energy electronic transitions with a high transition probability and possess a high capability to accept or release electrons. These properties account for the absorption color of polymethine dyes consisting of two mol. fragments. The scope and limitations of a composite-mol. approach are recognized by subjecting the electronic wave functions to configuration anal. Color-structure relations are derived from inspection of key orbital interactions between the mol. fragments.
calculations for sulfur-containing p-electron systems. 41. Evaluation of
alternative p-models for conjugated heterocycles. Fabian, Juergen. Sekt. Chem., Tech. Univ.
Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Physikalische Chemie (
Results of PPP-CA calcns. on heterocycles (e.g., I; X = NH, O, S, Se, Te) were tabulated. Configuration anal. of the state functions of the heterocycles gave a clear picture of the delocalization or localization of the p-electron systems.
The "Molecules in Molecule" (MIM) model and its application to p-electron systems. Part 1. Fabian, J.. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Signalaufzeichnungsmaterialien (1978), 6(4), 307-21.
A review with 75 refs.
The "Molecules in Molecule" (MIM) model and its use in p-electron systems. Part 2. Fabian, J. Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Signalaufzeichnungsmaterialien (1979), 7(1), 67-89.
A review with over 200 refs. with indications of the classes of compds. to which the quantum mech. approach is applicable. The mol. fragment technique can be related to phenomenol. concepts.
calculations on polymethines. XI. Local
spectral excitations in polynuclear cyanine dyes. Fabian,
J.; Zimmer, A. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer
Praktische Chemie (
Various branched-conjugated cyanine dyes display long wavelength absorption bands similar in position to those of their straight-chain substructures which, based on results of PPP-type calcns., can be attributed to partial localization of the electronic transition although the participating electronic states are highly localized. The long wavelength absorptions of sym.-branched trinuclear cyanine dyes have an entire mol. chromophore origin resulting from two-fold degenerate electronic transitions. Lowering of the symmetry results in splitting of the color band. In contrast, various tetranuclear cyanine dyes can be considered as being composed of 2 subchromophores either directly linked or joined through a conjugative bridge. PPP configuration anal. and LHM-type calcns. indicate that splitting of the color band is best understood by composite mol. approaches. In this context, the applicability of the simple vol. exciton theory is discussed.
The energy gap in polymethinestreptocyanines of infinite chain lengths. Tyutyulkov, N.; Fabian, J.; Polansky, O. E. Inst. Org. Chem., Sofia, Bulg. Zeitschrift fuer Naturforschung, Teil A: Astrophysik, Physik und Physikalische Chemie (1979), 34A(8), 1034.
Extrapolation of the exptl. detd. energies of the longest wavelength transition in the polymethinestreptocyanine series yields a value of 1.0 eV for the energy gap.
The absorption feature of conjugated compounds containing the NSN-chromophore. Fabian, J.; Mayer, R.; Bleisch, S. Sect. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Phosphorus and Sulfur and the Related Elements (1979), 7(1), 61-7.
The NSN group absorbs at relatively long wavelengths in the UV region. Because of its capability to release or to accept electrons, adjacent groups can produce a pronounced red shift of the color band. Based on the more recently described PPP configuration anal. technique and the MIM-LCI method the color detg. electronic transitions of org. sulfdiimides (Sulfurdiimines) are accounted for in terms of their constituent parts. The calcns. revealed that the position of the color band is mainly governed by frontier orbital interactions. Sym. junction of the NSN unit with conjugated fragments give deeply colored heterocyclic compds., if either their HOMO's or LUMO's have the same sym. and undergo an effective overlap. This condition is not fulfilled, in general, for compds. which are strongly stabilized in their electronic ground states.
When do organic compounds have color. Fabian, Juergen. Tech. Univ. Dresden, Ger. Dem. Rep. Biologiya i Khimiya (1979), 22(5), 9-16.
A review with no refs.
calculations on polymethines. XII. On
the intensity of intramolecular charge-transfer absorption bands. Fabian, J. Sekt. Chem., Tech. Univ.
Dresden, Dresden, Ger. Dem. Rep. Journal fuer
Praktische Chemie (
Some meropolymethine and zwitterionic dyes were considered according to 2 mol. fragmentation structures which have either donor or acceptor properties. In this model the color band originates from a charge-transfer transition. This transition gains sufficient intensity if some 2-orbital 2-electron interaction occurs between the HOMO of the donor and the LUMO of the acceptor fragment. The necessary precondition for this is equal symmetry of the pertinent donor and acceptor orbitals. Whereas ground stabilizing interfragmental overlap favors high transition probabilities, transition energies are raised, however. Intense long-wavelength absorption consequently necessitates a moderate degree of overlap.
Approaches for interpreting p electronic states and p electronic transitions. Fabian, J.; Mehlhorn, A.; Fratev, F. Chem. Dep., Tech. Univ., Dresden, Ger. Dem. Rep. International Journal of Quantum Chemistry (1980), 17(2), 235-53.
Scope and limitations of different approaches which enable p electronic systems of topol. equiv. structures to be compared were examd. Particular attention was paid to analyses in terms of mol. subsystems.
Importance of the molecular orbital and configuration analysis in describing molecular properties. Fabian, Juergen. Sekt. Chem., Tech. Univ., Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1980), 20(6), 197-203.
A review with 53 refs.
Light Absorption of Organic Colorants: Theoretical Treatment and Empirical Rules. Fabian,
Juergen; Hartmann, Horst. Fed. Rep.
Nature of the 1,4-naphthoquinone chromophore. Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1980), 20(8), 299-300.
The absorption spectra of 1,4-naphthoquinones were analyzed via correlation diagrams using the projection method of H. Baba, et al. (1969). The long-wavelength bands of I (R = Cl, MeO) have quinoid character.
structure and properties of polynuclear aromatic ketones and quinones. VIII.
Interpretation of the 9,10-anthraquinone chromophore by configuration
analysis. Fabian, Juergen; Nepras,
CI anal. was used to assign the electronic spectral bands of anthraquinone. The longest wavelength absorption band at 320 nm is actually localized in the benzene fragments. The electronic excitation is mainly due to Lb excited states of benzene. The 2nd benzenoid band at 251 nm has a more complex role. Although the interpretation of the 270-nm band as a quinoid band is suggested, the correlation is rather poor. Configuration anal. supports the description of anthraquinone in terms of two benzoyl halves. The level sequence and energy position of the p-p* excited states of anthraquinone are satisfactorily reproduced by the equiv. synthetic approach (LHM calcns.). The spectra of substituted anthraquinones are interpreted in terms of local anthraquinone excitations and charge-transfer excitations.
structure and properties of polynuclear aromatic ketones and quinones. IX.
Interpretation of electronic spectra of linear polynuclear p-quinones by
the method of configuration analysis. Nepras, Milos;
Fabian, Juergen; Titz,
Correlation graphs of states were constructed enabling interpretation of the UV in terms of local transitions in the fragments and charge-transfer transitions between the fragments. The effect of annulation on the first pp* absorption band was examd. qual. by the interaction of the fragment frontier MOs. MO model fully agrees with the exptl. absorption bands and the PPP calcd. UV.
On the appropriateness of "molecules-in-molecule" models in describing of p-electronic states of composed aromatic systems. Fabian, J.; Scholz, M. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Theoretica Chimica Acta (1981), 59(2), 117-25.
Configuration anal. allows the straightforward derivation of electronic-state correlation diagrams and the crit. examn. of the appropriateness of simple mols.-in-mol. approaches. Fluoranthene is taken as an example. The advantage of the composite-mol. approach is demonstrated by using energy spectra of fluoranthene analogs.
Quantum chemical analysis and interpretation of UV spectrum of furfurylideneaniline. Mehlhorn, Achim; Fabian, Juergen; Perez, Carlos. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1981), 21(6), 225-6.
The effect Ph-ring rotation on the UV spectrum of RCH:NPh (R = 2-furyl) was established with the aid of CNDO/S calcns.
MO-LCAO calculations on polymethines. XVI. Substituent effects on heterocyclic polymethine chromophores with intramolecular charge-transfer character. Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1981), 21(7), 263-4.
The electronic spectral shifts induced in the model fragment I by Me2N and CN groups in the different positions were calcd., and the use of a polymethine or an intramol. charge-transfer model was discussed.
Organic sulfur-nitrogen radicals. V. Substituent dependence of the spin density at nitrogen-containing p radicals in the doublet ground state. Gey, Erhard; Fabian, Juergen; Bleisch, Siegfried; Domschke, Guenter; Mayer, Roland. Zentralinst. Phys. Chem., DAW, Berlin, Ger. Dem. Rep. Zeitschrift fuer Chemie (1981), 21(7), 265-6.
A linear relation between the hyperfine splitting consts. (aN) for title radicals I (R = MeO, Me, H, Cl, Br, CF3, CO2Et) and Hammett sp consts. and the results of MO calcns. indicated that I was indeed the correct structure for these radicals.
MO-LCAO calculations on polymethines. XIII. Spectral effects resulting from the cyclization of cyanine chains. Fabian, J.. Sekt. Chem., Tech. Univ., Dresden, Ger. Dem. Rep. Journal fuer Praktische Chemie (Leipzig) (1981), 323(4), 551-60.
The longest-wavelength absorptions of various heteroarom. and substituted benzenes, which are formally derived from polymethine cyanines, are satisfactorily described in terms of the resp. chain-ref. structures. PMO-theor. arguments based on frontier orbitals are justified in most cases, and provide correct predictions as to whether the color bands of streptopolymethines are displaced to shorter or longer wavelength on cyclization.
MO-LCAO calculations on polymethines. XIV. Alternative fragmentation modes in describing benzenoid chromophores. Fabian, J. Sekt. Chem., Tech. Univ., Dresden, Ger. Dem. Rep. Journal fuer Praktische Chemie (Leipzig) (1981), 323(4), 561-70.
o-H2NC6H4CN (I) is used as an example to illustrate the applicability of alternative fragmentation modes. State-correlation diagrams of I with respect to the corresponding open-chain heptamethine-merocyanine and composite mols. consisting of PhNH2 or PhCN and a substituent group, derived by MO/CI calcns., indicate that reasonable conclusions regarding the bathochromic effect can be made using the polymethine model.
Fundamentals of a modern concept of color-structure relations. Fabian, J. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Signalaufzeichnungsmaterialien (1981), 9(3), 165-76.
A quantum chem. approach to color-structure relations was described.
Studies of the
energy spectrum of a,w-substituted polymethine chains. II.
Polymethine chains with odd number of methine groups.
Tyutyulkov, Nikolay; Dietz, Fritz; Fabian, Juergen; Melhorn, Achim; Tadjer,
Exptl. data for the energy (De) of the longest wavelength optical transitions of substituted polymethines, X(CH)2n+1X, show that, as n ® ¥, De has a finite, nonzero value. The energy gap of odd polymethines is the same as that of the even polymethines - the polyenes (DE¥.apprx.2 eV). The substituents (X = N, O, B) are responsible for the appearance of levels in the gap. These are vacant (X = B) or occupied (X = N, O). The transition from or to such a level dets. the longest wavelength optical transition energy of polymethines.
Fluorescence of 5H-benzo[a]phenothiazin-5-ones. Fischer, Mechthild; Fabian, Juergen; Mann, Gerhard; Wilde, Horst; Lepom, Peter. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1981), 21(10), 361-3.
absorption and fluorescence spectra of I (R = Et2N, Cl; R1 = Me, Bu, BuO, BuS,
NH2, PrCO) were recorded in solvents of different polarity. The fluorescence intensity of I (R = Et2N)
was highest when R1 = PrCO and lowest when R1 = BuO, BuS, or NH2. The lowest intensity was exhibited by I (R =
Cl, R1 = Me). The spectra of I (R =
Et2N, R1 = Me) was interpreted via
structure and physical properties of thionitroso compounds - a quantum chemical
A.; Sauer, J.; Fabian, J.; Mayer, R. Sekt. Chem., Tech. Univ.
Semi- and nonempirical quantum-chem. methods were used to describe the electronic structure and phys. properties of unknown thionitroso compds. Predictions on geometry, electron distribution, ionization potential, electron affinity, UV spectra, and the S0-T1 energy splitting of these compds. were made. First exptl. results on thionitroso compds. were examd. critically.
Aromatic electronic delocalization of benzo derivatives of five-membered heterocycles. Mehlhorn, Achim; Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep.Croatica Chemica Acta (1981), 54(4), 427-34.
The aromaticity of some bicyclic heterocycles is discussed with the aid of configuration anal. of the expansion-coeff. matrixes and similarity anal. of the d. matrices. The iso-p-electronic  annulenyl anion is taken as the arom. ref. compd. for all the heterocyclic compds. considered. Anal. of the electronic structure reveals different aspects of the aromaticity than that of the energetics. In addn., the question is posed whether the substructures display arom. features.
Benzalanilines and 2-phenylindolenines - characterization of their excited electronic states and interpretation of their UV spectra. Mehlhorn, Achim; Fabian, Juergen; Perez, Carlos. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Praktische Chemie (Leipzig) (1982), 324(2), 267-78.
UV spectra of I and II (R = R1 = H; R = H, R1 = Me2N; R = Me2N, R1 = H; R = H, R1 = NO2; R = NO2, R1 = H) were calcd. using PPP and CNDO/S methods. The PPP results compared better with exptl. data the CNDO/S results. The origin for the peculiar spectral pattern of I with respect to II was the non-coplanarity of the former. Due to the coupling of the pp* and np* states, two new excited states of mixed character emerge. These states cause two transitions of modified energies and medium oscillator strengths, which are mainly responsible for the spectral features of benzalaniline and its derivs.
MO-LCAO calculations on polymethines. XV. Nature of the cryptocyanine chromophore and fluorophore. Fabian, Juergen; Dietz, Fritz; Tyutyulkov, Nikokai. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Acta Chimica Academiae Scientiarum Hungaricae (1982), 109(4), 389-98.
The singlet-singlet transitions of I are calcd. by the PPP method with CI including the lowest energy doubly and triply excited configurations. The red and blue fluorescences are due to S1 ® S0 and S2 ® S0 transitions, resp. A wave function anal. shows that both these transitions and the states S1 and S2 are fully delocalized. The lowest-energy doubly excited configuration is a major contributor to S2. Mol. relaxation of the Franck-Condon excited state is stronger for the planar S2 than for the planar S1 state. While the formation of a nonplanar mol. in the S2 state cannot be excluded, its occurrence would affect only the nonradiative decay from S2.
MO-LCAO calculations on sulfur-containing -electron systems. XLVI. Electronic excitation of organosulfur
J.; Mayer, R.; Bleisch, S.; Zahradnik, R. Sekt. Chem., Tech. Univ.
Transition energies of neutral and ionic sulfur contg. heterocyclic radicals have been calcd. by the method of Longuet-Higgins and Pople and compared with the exptl. excitation energies obtained by UV/VIS absorption and photoelectron spectroscopy. In most cases the calcd. transition energies satisfactorily match the ones found exptl. A few compds. behave exceptionally. Discrepancies between the two sets of exptl. values are attributed to different mol. geometries of the radical species. According to the calcns., the UV/VIS absorption spectra of recently synthesized sulfur and nitrogen contg. radicals are compatible with the 1,2,3-dithiazolyl structure.
Structure investigation of 4-methyl-6-phenyl-2-(thiobenzoylmethylene)-2H-thiapyran. Kaiser, J.; Hantschmann, A.; Richter, R.; Scheibe, R.; Fabian, J.. Sekt. Chem., Karl-Marx-Univ. Leipzig, Leipzig, Ger. Dem. Rep. Tetrahedron (1982), 38(11), 1639-45.
The structure of the title compd. [(E)- and (Z)-I] was examd. by ESCA, x-ray crystallog. anal. [on (Z)-I], and quantum chem. calcns. A no-bond interaction between the S atoms is caused by p-type interaction rather than by Coulomb-type interaction.
p-Electronic structure of a new class of simple closed and open shell polymethines. Fabian, Juergen; Mehlhorn, Achim; Tyutyulkov, N. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Doklady Bolgarskoi Akademii Nauk (1982), 35(3), 335-8.
The electronic structures and spectra of several boropolymethines were calcd. by the PPP method. These compds. belong to the [N] p or [N-1] p polymethine class.
Calculations on the molecular structure of simple boron-containing polymethine dyes. Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1982), 22(12), 452-3.
The MINDO/3 method was used to calc. the mol. geometries of [H2N(CH)nNH2]+ (n = 5, 6), [H2B(CH)nBH2]- (n = 5, 6), and [H2N(CH)nBH2].bul. (n = 5, 6). The C-B bond lengths were .apprx.140 pm. The alternation of bond angles and C-H bond lengths in these species was discussed.
structure and properties of polynuclear aromatic ketones and quinones. X.
Electronic absorption, fluorescence, and polarization spectra of 1- and
2-amino-9,10-anthraquinones and their interpretation by the method of configuration
Milos; Fabian, Juergen; Titz, Milos; Gas, Bohuslav. Res. Inst. Org. Synth.,
The absorption frequency-dependent polarization fluorescence spectra and linear dichroism in stretched (oriented) poly(vinyl alc.) are used to assign the UV at 250-600 nm, of the title compds. The electronic structure of the excited states and the UV are also calcd. by a PPP method with configuration anal.
structure and properties of polynuclear aromatic ketones and quinones. XI.
Electronic absorption, fluorescence, and polarization spectra of a,a'-diamino-9,10-anthraquinones
and their interpretation by the method of configuration analysis. Nepras, Milos; Gas, Bohuslav; Fabian,
Juergen; Titz, Milos. Res. Inst. Org. Synth.,
The absorption frequency-dependent polarization fluorescence spectra and linear dichroism in stretched (oriented) poly(vinyl alc.) are used to assign the UV, at 250-600 nm, of the title compds. The electronic structure of the excited states and the UV are also calcd. by a PPP method with configuration anal.
Electronic structure and properties of
polynuclear aromatic ketones and quinones.
XII. Electronic absorption,
fluorescence and polarization spectra of ,'-diamino-9,10-anthraquinones and
their interpretation by the method of configuration analysis. Nepras, Milos; Titz,
The absorption spectra of 2,3-diamino-, 2,7-diamino-, and 2,6-diamino-9,10-anthraquinones was interpreted on the basis of adsorption frequency-dependent polarization spectra of fluorescence and dichroism on oriented polyvinyl alc. sheets. The excited pp* were characterized by PPP configuration anal. calcns. For all 3 isomers, the 1st 2 transitions had a pronounced charge-transfer character. With the 2,3-isomer, the 3rd and 4th transitions are purely local; with the 2,6- and 2,7 isomers, the 3rd and 4th transitions are mixts. of local and charge-transfer transitions.
structure and properties of polynuclear aromatic ketones and quinones. XIII.
Electronic absorption, fluorescence and polarization spectra of a,b-diamino-9,10-anthraquinones
and their interpretation by the method of configuration analysis. Nepras,
The absorption spectra of 1,2-diamino-, 1,3-diamino-, 1,6-diamino-, and 1,7-diamino-9,10-anthraquinones were interpreted on the basis of adsorption frequency-dependent polarization spectra of fluorescence and dichroism on oriented polyvinyl alc. sheets. PPP calcns. were used to investigate the excited states. The 1st excited state of a,b-diamino-9,10-anthraquinones has a predominant charge-transfer character with charge transfer from the a-amino group. The 2nd excited state has a predominant charge-transfer character with charge transfer from the b-amino group.
electron correlation on the spectra of streptopolymethines. Dietz,
F.; Fabian, J.; Olbrich, G.; Tyutyulkov, N.; Kanev,
PPP CI calcns. (including doubly excited configurations) of the UV of the title compds. show that electron correlation is important.
Spectral properties of [N + 1]p streptopolymethine radicals. MO-LCAO calculations on polymethines. Part XVII. Fabian, J.; Daehne, S. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. THEOCHEM (1983), 9(3-4), 217-29.
[N + 1]p Streptopolymethine radicals are expected to display two long-wavelength absorption bands in the UV/VIS region, with the first one of lower and the second one of higher intensity. The close relationship between the open-shell polymethine radicals and the closed-shell polymethine dyes is reflected both by the large const. vinylene shift of the longest wavelength transition and by the alternant substituent effect on it. Hence, the [N + 1]p polymethine radicals are clearly distinguished from [N]p hydrocarbon radicals (vinylogous allyl radicals).
What is the basic chromophore of a dye? Fabian, Juergen; Mehlhorn, Achim; Dietz, Fritz; Tyutyulkov, N. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Monatshefte fuer Chemie (1984), 115(1), 21-34.
Taking 4,5-diphenyl-2-(dimethylamino)-3-azacyclopentadienone (I) [58329-07-0] as an example, its color was discussed in relation to different basic chromophores (parent chromophores). The parent chromophore can be defined either as the structure which has nearly the same absorption wavelength as the dye under consideration or as the substructure which is electronically most closely related to the dye. In the case of I both considerations lead to different results. Based on the correlation diagram between the electronic states involved in the electronic excitation, the long-wavelength absorption of I is better understood in terms of the merocyanine parent chromophore than in terms of a betainic substructure, which should have the same color as I and is the parent chromophore according to M. Klessinger (1978). This conclusion is drawn from PPP configuration anal. of the wavefunctions of I relative to different mol. substructures. The mol. geometry predicted by the geometry-optimized MINDO/3 and QCFF/Pi calcns. provide addnl. arguments in favor of the cyclomerocyanine structure of I. In respect to the color, I belongs to a new series of cyclic-conjugated chromophoric systems.
Quantum chemical studies on the molecular and electronic structure of simple azomethinimines and related compounds. Mehlhorn, Achim; Fabian, Juergen; Kulpe, Siegfried. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Praktische Chemie (Leipzig) (1984), 326(2), 303-10.
The mol. and electronic structure of simple azomethinimines are examd. by MINDO/3 and CNDO02 calcns. The calcd. mol. geometry is compared with x-ray results. Except for the NN-bond lengths MINDO/3 satisfactorily describes the mol. structure of azomethinimine and related p-electronic systems. The charges at the atoms along the conjugated chain are alternating as in polymethines. The terminal C carries a neg. charge. This charge brings about an appreciable shielding of this C as found in the 13C-NMR spectrum. This results does not contradict a stabilization of azomethinimines in the crystal via :CH×××O:C interactions.
Structure and spectral properties of a new class of polymethines. Tyutyulkov, N.; Kurtev, B.; Stefanovskii, I.; Dietz, F.; Fabian, J.; Melhorn, A.; Olbrich, G.; Polansky, O. E. Inst. Org. Chem., Sofia, Bulg. Journal of Molecular Structure (1984), 114 279-82.
MO calcns. of 5-membered cyclic polymethines, e.g. I (R not given), show that the longest wavelength absorption band is bathochromically shifted from that in the related streptopolymethines. The electron configuration and d. in cyclopentadienyl cation is related to that expected for the 5-membered ring in this dye class.
MO-LCAO calculations on polymethines. Part XIX. Ground and excited state geometries of closed and open shell [N + 1] p-streptopolymethines. Fabian, Juergen; Mehlhorn, Achim. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. THEOCHEM (1984), 18(1-2), 17-26.
Mol. geometries of simple cyanines and merocyanines and their radical congeners are predicted by MINDO/3 calcns. A high degree of C-C bond length equalization is found for cyanines both in the ground and lowest excited pp states, whereas C-C bond length alternation dominates in the mol. ground state of merocyanines. This result coincides with exptl. found bond lengths of closed shell cyanines and merocyanines in the mol. ground state. In agreement with expt., the Stokes shift between the max. of absorption and fluorescence decreases for cyanines in ascending chain length, but increases for longer chain merocyanines. The polymethinic structure of the cyanines and the polyenic structure of the merocyanines are also reflected in the distinct bond strength and energetic stabilization effect of donor and acceptor substituents at different sites of the trimethine chain. The bond lengths of simple violene radicals in the ground state are closely related to those of the nonradical cyanines and similarities are found in the substituent effects as well.
MO-LCAO calculations on polymethines. Part XX. The effect of cyclization on the molecular geometry of closed shell [N + 1] p polymethines. Mehlhorn, Achim; Fabian, Juergen. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. THEOCHEM (1984), 18(1-2), 27-38.
The bond lengths of cyclized cyanines and merocyanines are predicted by MINDO/3 and QCFF/Pi (quantum mech. consistent force field method for p electron systems) calcns. Extremely long C bonds (rCC > 151.7 pm) are found for some compds. that belong to Daehne's nonalternant polymethines and fulfill Kulpe's charge repulsion rule. According to the calcns., shortening of the long bond occurs upon excitation from the electronic ground to the lowest excited pp* state. Since this excited state is stabilized, the energy gap to the ground state is low and relatively long wavelength absorptions are predicted for such compds. Alternatively, these cyclized polymethines may be considered as derivs. of antiaroms. that bear N or O contg. substituents. Exptl. data available are in accordance with the theor. results.
calculations on polymethines. XXI. Electrono-dative, electrono-captive, and
electrono-ambident polymethine radicals. Fabian, J.; Hartmann, H. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer
Praktische Chemie (
An MO treatment is used to place polymethine radicals into the title classifications, which are defined. Substituent do effect the redox properties of the polymethine radicals.
a new class of persistent radicals. Mayer, Roland; Domschke, Guenter; Bleisch,
Siegfried; Fabian, Juergen; Bartl, Anton; Stasko, Andrej. Sekt.
Chem., Tech. Univ. Dresden,
The title radicals were formed and their ESR and electronic spectra examd. Delocalization of the unpaired electron over the whole radical was found.
Principles for the qualitative characterization of the energy and the electronic structure of the ground-state barriers and of the non-spectroscopic minima in the trans-cis isomerization of polymethines and polar polyenes. Dietz, Fritz; Fabian, Juergen; Mehlhorn, Achim; Tadjer, Alia; Tyutyulkov, N. Sekt. Chem., Karl-Marx-Univ., Leipzig, Ger. Dem. Rep. Wissenschaftliche Zeitschrift - Karl-Marx-Universitaet Leipzig, Mathematisch-Naturwissenschaftliche Reihe (1984), 33(4), 390-6.
A quantum chem. treatment yielded 10 rules for the ground-state barrier height and the position of the nonspectroscopic min. for rotation of a mol. fragment during trans-cis isomerization at different bonds in sym. and unsym. polymethines (cyanines and merocyanines) and polar polyenes (protonated Schiff bases of polyenals) as well as the electronic structure of the mol. fragment rotated by 90°. The isomerization mechanism was discussed on the basis of these rules.
The chromophore of fulvenoid dyes. Fabian, J.; Junek, H. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Dyes and Pigments (1985), 6(4), 251-65.
Synthesis of the deeply colored 1,2,3,4-tetrachloro-pentafulvene-6,6-dicarbonitrile [84808-78-6], the 1st representative of the 6,6-di-acceptor-substituted fulvenes, initiated a study of the relations between color and constistution of 6,6-diamino- and 6,6-dicyanopentafulvene, cyclopentadienone, and the cyclopentadienon-immonium ion. The main tool of this study was the MO and configuration anal. method according to H. Baba, T. Takemura, and S. Suzuki (1969) within the framework of the variable b PPP method. A clear interpretation was achieved in terms of both iso-p-electronic delocalized and localized ref. structures.
Color of pseudooxo croconic acid bisamides. Fabian, Juergen; Junek, Hans. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Monatshefte fuer Chemie (1985), 116(5), 625-32.
The color of oxo- and pseudooxo croconic acid bisamides I [X = O, C(CN)2] in soln. is due to 2 intense p ® p* transitions in the visible region. These transitions are related to those of the Klessinger-Luettke basic indigo chromophore. The 1st band corresponds to the 2nd absorption band of this basic chromophore red-shifted by the intramol. charge transfer excitation between the mol. subsystems of I. The 2nd band of I is closely related to the color band of the basic indigo chromophore. According to the results of various anal. and projection techniques the interpretation of the color of I in terms of the basic indigo chromophore is superior to any other one in terms of alternative chromophoric subsystems.
MO-LCAO calculations on sulfur-containing p systems. 45. Quantum-chemical ab initio calculations on organosulfur compounds: experimental and theoretical studies on thioformaldehyde and dithioglyoxal. Fabian, Juergen; Mayer, Roland; Carsky, Petr; Zahradnik, Rudolf. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1985), 25(2), 50-61.
A review with 145 refs. including the mol. geometries, electronic structure, MO energies, etc., of the title compds.
double-minimum potential curves for XY3 pyramidal molecules. Spirko, Vladimir; Civis, Svatopluk; Beran,
Stanislav; Carsky, Petr; Fabian, Juergen. J. Heyrovsky Inst. Phys. Chem.
The reduced potential curve (RPC) method used by Jenc and Pliva (1963) for studying the diat. potentials is adapted for three-parameter studies of the inversional double-min. potential functions of XY3 pyramidal mols. Reduced double-min. potential curves (RDMPC's) of the first, second, and third row hydrides (CH3-, NH3, OH3+; SiH3-, PH3, SH3+; GeH3-, AsH3, SeH3+) are constructed using CNDO/2 and ab initio MBPT(2) theor. potentials. The theor. RDMPC's corresponding to a group of isoelectronic hydrides coincide to a high degree of approxn., so that they can be represented by a single curve. Furthermore, there is a nearly perfect coincidence between the theor. RDMPC's of the first row hydrides and the NH3 exptl. RDMPC (the only curve known exptl.). To illustrate a practical use of the proposed RPC approach, several approximants to the genuine PH3 potential are constructed by combining the available exptl. data and the calcd. RDMPC's. The resulting potential exhibit a very close coincidence.
MO-LCAO calculations for sulfur-containing p-electron systems. 46. Ab initio calculations for cyclic conjugated disulfides. Fabian, Juergen. Sekt. Chem., TU Dresden, Dresden, Ger. Dem. Rep. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (1985), 34(4), 36.
Bond lengths and total energies were calcd. for title compds. I, II, and III and for their open-chain valence isomers. CH(S-):S is more stable than I and S:CHCH:S is somewhat more stable than II. III is more stable than its open-chain isomer.
An efficient UMP2
program. Carsky, P.; Fabian, J.; Hess, B. A., Jr.; Schaad, L.
J. J. Heyrovsky Inst. Phys. Chem.
Timings are reported for 6-31G*/UMP2 (second-order many-body perturbation theory) calcns. on planar allene, twisted ethylene, cyclopropenyl anion, allyl, Et, iso-Pr and CF3 radicals performed by means of the programs GAUSSIAN 80 and HONDO UMP2. The comparison of the two programs is used for pointing out several factors affecting the speed of MP2 calcns.
Structure and spectral properties of a new class of polymethines. I. Cyclopentamethines. Tyutyulkov, N.; Kurtev, B.; Stefanovski, Yu.; Fabian, J.; Mehlhorn, A.; Dietz, F.; Polansky, O. E.; Olbrich, G. Inst. Org. Chem., Sofia, Bulg. Izvestiya po Khimiya (1985), 18(3), 318-29.
PPP-CI, MINDO/3 and ab initio calcns. of geometries, charge densities, and UV spectra of 5-membered cyclic polymethines show that their structures closely resemble the anti-arom. cyclopentadienyl cation.
model of indigoids. Part 2. Vinylogous H-chromophores. Daehne,
S.; Fabian, J. Zentralinst. Opt. Spektrosk., Akad. Wiss. DDR,
HMO-bSC calcns. of H-chromophore indigoids and their vinylogous analogs show that, in the central bond vinylogs, elongation is assocd. with red-shifted light absorption when the symmetry of the p-electron distribution within the crossed polymethine chains is maintained (i.e., const. symmetry deviation). The exptl. obsd. blue-shift is due to an increased symmetry deviation as a result of the formation of polyenic regions. Obsd. red-shifts are due to the one-sided formation of a merocyanine substructure within the H-chromophore whose vinylene shift decreases with increasing chain length.
Studies of the energy spectrum of w,w'-substituted polymethine chains. III. Many-atom substituents. Tyutyulkov, N.; Polansky, O. E.; Dietz, F.; Fabian, J.; Mehlhorn, A. Inst. Org. Chem., Sofia, Bulg. Theoretica Chimica Acta (1986), 69(3), 247-58.
On substitution of polymethines R-(CH)N-R with a complex many-atom substituent R-, the energy gap of polymethine chains (N ® ¥) may have states which are responsible for long-wavelength transition. For certain substituents, the energy of the electron/transitions may be .mchlt.1 eV, i.e. the transitions may be in the near-IR.
calculations on sulfur-containing p-electron systems. XLIX.
Tetramethine bridged derivatives of the oxalic acid - novel colored
pigments of indigoid structure. Beckert,
R.; Fabian, J.. Sekt. Chem., Tech. Univ.
Dresden, Dresden, Ger. Dem. Rep. Journal fuer
Praktische Chemie (
RC(S)NH2 (I; R = alkyl, aryl, dialkyl- or diarylamino, alkoxy, aryloxy, alkyl- or arylthio) with ClCOCOCl gives the corresponding D2-thiazoline-4,5-diones II which are precursors of the synthons RC(S)N:C:O; the reaction of I (R ¹ alkyl) fails with ClC(:NR1)C(:NR1)Cl (III; R1 = aryl). I (R = Me) and III (R1 = Ph, 4-MeC6H4, 4-MeOC6H4, 4-EtO2CC6H4, 4-O2NC6H4) give the corresponding blue polymethine pigments IV and/or its isomers via the oxidative dimerization of the intermediate 2-methyl-D2-thiazoline-4,5-diimides V or their tautomers. A PPP calcn. of the UV of IV shows that it has the H indigo chromophore and that exists as the shown tautomer. IV consists of 2 sym. crossed polymethine chains.
MO-LCAO calculations on sulfur-containing p-electron systems. L. Synthesis and UV/VIS spectral properties of derivatives of 1H-perimidine-2-dithiocarboxylic acid. Thiel, W.; Fabian, J.; Friebe, B. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Praktische Chemie (Leipzig) (1986), 328(5-6), 812-23.
Esters of the 1H-perimidine-2-dithiocarbonic acid are easily accessible from 1,8-diaminonaphthalene and chloroacetyl chloride and subsequent thiolation of the reaction product under mild conditions followed by alkylation. The dithioesters react with aliph. and arom. amines to form thioamides. Both the resulting dithioesters and thioamides are clearly distinguished by their color from the vast majority of known derivs. of thioncarbonic acids. Dithioesters and thioamides are generally red and yellow, resp., in soln.; the corresponding derivs. of the 1H-perimidine are blue and red, resp. The detailed examn. of the exptl. data has revealed that the color detg. longest wavelength absorption bands are due to the p ® p* rather than to the n ® p* transitions. Due to the efficient mixing of the lowest energy locally excited state of the heterocyclic moiety and the lowest energy perimidine-to-substituent charge transfer state the low-intensity longwavelength p ® p* transition of perimidine undergoes a pronounced red shift by acceptor substituents of high electron affinity in 2-position. This interpretation of the deep color of the 1H-perimidine-2-thiocarbonic acid is in harmony with substituent effects and fully born out by PPP type calcns. completed by addnl. analyses of electronic state (Baba-Suzuki-Takemura anal.) and electronic transitions (Ohta-Kuroda-Kunii anal.).
MO LCAO calculations on polymethines. XXII. Antiaromatic cyclopentadienyl cations. Mehlhorn, Achim; Fabian, Juergen; Tyutyulkov, Nikolay; Olbrich, Gottfried; Dietz, Fritz. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Journal fuer Praktische Chemie (Leipzig) (1986), 328(4), 603-11.
Ab initio SCF and semiempirical MINDO/3 and PPP/DCI calcns. have been applied to substituted cyclopentamethines which formally resulted from cyclization of streptopentamethines in the a,a'-positions. These compds. exhibit a typical streptopolymethinic charge distribution of the carbon atoms along the cyclized chain, unique mol. geometries, extremely small energy gaps between the lowest excited states S1, T1 and the ground state S0 as well as large electron affinities. With respect to mol. geometry, spectral behavior and electron affinity, substituted cyclopentamethines are closely related to the antiarom. cyclopentadienyl cation (I). Depending on the substitution pattern, the one or the other of the two Jahn-Teller distorted geometries of the antiarom. I appears to be frozen.
MO-LCAO calculations on polymethines. XXIII. The origin of the absorption color of dithizone and related compounds. Fabian, J.; Roebisch, G.; Noeske, R. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Dyes and Pigments (1987), 8(3), 165-77.
The two intense absorption bands of dithizone [60-10-6] at about 440 and 620 nm give rise to the green color obsd. in soln. In contrast to the review prevailing in the literature, the two color bands are due to a single tautomer that has the diazatrimethinium thiolate rather than thiocarbazone or mercaptoformazan structure. This follows from quantum-chem. supported color-structure relation between dithizone and related compds. Chromophorically dithizone belongs to the cyanine dyes. Internal substitution of CH of the trimethine chain by aza-type N atoms and addnl. meso-substitution by thiolate sulfur imparts to the trimethine cyanine a significant bathochromicity and brings about its unique chromophoric properties due to its two intense color bands.
conjugated organic compounds. Fabian,
Juergen. Sekt. Chem., Tech. Univ. Dresden,
The failure of the classically derived color structure relations of the triad theory (which apply to polyene, polymethine, and arom. chromophores) to nonclassical non-Kekule structures, e.g. I, II, III, is discussed.
Ab initio study on simple biradicaloid thio-nitroso compounds. Fabian, Juergen; Mehlhorn, Achim. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1987), 27(1), 30-1.
Ab initio MP2 calcns. for HNS gave optimized geometries, total energies, and dipole moments for the singlet and triplet states. Similar calcns. were performed for H2C:S and MeN:S. The results show that simple thionitroso compds. exist in the singlet state and are excited with very small energy to the triplet state indicating a biradical character.
The molecular structure of substituted cyclopentadienyl cations. Fabian, Juergen; Mehlhorn, Achim; Tyutyulkov, N. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. THEOCHEM (1987), 36, 355-63.
Internal or external substitution of the cyclopentadienyl cation brings about hetero- or carbocyclic compds. that differ greatly in their electronic and mol. structure. Depending on the substitution pattern and the nature of the heteroatoms the compds. constitute two series. Each series is related to one of the two Jahn-Teller distorted structures of the parent cyclopentadienyl cation. This classification follows from qual. MO interaction schemes which are fully consistent with correlation diagrams obtained by MO anal. Semiempirical MINDO/3, MNDO and STO-2G ab initio calcns. of the mol. geometry of N and B-substituted cyclopentadienyl cations furnished evidence in favor of their classification into two series of distorted structures.
MO-LCAO calculations on sulfur-containing p-electronic systems. Part LI. Synthesis and electronic structure of potentially valence isomeric 1,2-dithiolylium-4-olates. Mayer, R.; Fabian, J.; Viola, H.; Jakisch, L. Sekt. Chem. Tech., Univ. Dresden, Dresden, Ger. Dem. Rep. Phosphorus and Sulfur and the Related Elements (1987), 31(1-2), 109-22.
Substituted 1,2-dithiolylium-4-olates I (R = R1 = SMe, Ph, 4-Me2NC6H4; R = SMe, R1 = morpholino; R = 4-Me2NC6H4, R1 = SMe, morpholino) are obtained by thiolation of 1,3-dichloropropane-2-one or pyruvic thiomorpholide with S and Et3N in DMF and subsequent alkylation. Condensation with Me2NPh or morpholine gave the amino derivs. IR and UV/VIS spectra of the bis(methylthio), methylthio dimethylaminophenyl and bis(dimethylaminophenyl) compds. provide evidence in favor of the cyclic structure I whereas the spectra of the bis(amino) and amino methylthio compds. are compatible with non-cyclic valence isomeric structures RCSCOCSR1 (II). Both I and II react with acids to form 4-hydroxy-1,2-dithiolylium salts. The color-structure relationships of 1,2-dithiolylium-4-olates were examd. by PPP-type calcns. The lowest excited states and the color detg. transitions are accounted for in terms of the dithiolylium and olate moieties. The neg. solvatochromism of the color bands of I is related to the marked amt. of oxygen-to-dithiolylium charge transfer of the lowest-excited p®p* transition. In larger mols. such as I (R = R1 = 4-Me2NC6H4) the color is governed by the lowest electronic transition of polymethine-type subchromophores rather than that of the intramol. charge transfer chromophores and, therefore are pertinent to cyanine dyes.
Quantum-chemical and picosecond studies of the excited states of thioindigoid dyes. Fabian, J.; Krysanov, A. S.; Alfimov, M. V. Tech. Univ., Dresden, Ger. Dem. Rep. Doklady Akademii Nauk SSSR (1987), 294(3), 653-5 [Phys. Chem.].
Quantum-chem. calcn. of the absorption spectrum for trans-thioindigo in lowest excited state revealed that the band which appears at 610 nm in the picosecond photolysis spectrum of this dye can be attributed to the Sn ¬ S1 transition.
PPP-type calculations on pp*-chromophores of betainic thiolates and related compounds. Fabian, J.. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Izvestiya po Khimiya (1987), 20(4), 562-8.
The failure of the conventional PPP method in predicting the position of the color band of mesoionic compds. with exocyclic oxo and thioxo groups is examd. Although the deeper origin of this failure is due to the underestimation of charge and correlation effects inherent to the biradicaloid structure of the compds., improvement in numerical prediction is simply achieved by replacing the std. parameters of the oxo and thioxo group by the empirical heteroatom parameters used in treating phenolates (Tichy, M., and Zahradnik, R., 1969) and thiophenolates (Kwiatkowski, J. S., et al., 1970). Thiopyrylium- and dithioylium-thiolates, as well as of N-thioxides of azaheterocycles, are predicted to be deeply colored. The longest-wavelength absorption of more extended betainic chromophores such as those of various neg. solvatochromic dyes are still satisfactorily reproduced by means of std. parameter sets.
Quantum chemical study on the photoisomerization of push-pull polyenes (streptomerocyanines). Mehlhorn, A.; Fabian, J.; Dietz, F. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Izvestiya po Khimiya (1987), 20(4), 569-78.
Semiempirical calcns. in the PPP-SCI, PPP-DCI, QCFF/PI, and MINDO/3 approxns. were used to est. potential energy curves of rotation around C-C double bonds of a homologous series of streptomerocyanines H2N(CH:CH)nCHO (n = 1-4). The shape of these curves in the S0 and S1 states is analyzed and discussed with respect to E,Z-photoisomerization processes.
MNDO calculations of organosulfur compounds. Fabian, Juergen; Birner, Peter. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (1988), 37(3), 119-23.
The mol. structures of 35 alicyclic and cyclic organosulfur compds. were calcd. by the MNDO method. The optimum geometries, calcd. by a gradient method, were compared with exptl. mol. structures and results of calcns. applying an empirical force field and a theor. one (ab initio calcns.). The heats of formation, dipole moments, and ionization energies of some of the compds. were also calcd.
MO-LCAO calculations of sulfur-containing p-electron systems. Part LIV. A theoretical study of the disulfide/dithione valence isomerism. Fabian, Juergen; Birner, Peter. Dep. Org. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Collection of Czechoslovak Chemical Communications (1988), 53(9), 2096-115.
According to MNDO calcns. on I, II, and III, closed-ring compds. are thermodynamically more stable than the open-chain compds. whereas the reverse holds for 4-methylene-1,2-dithiole. Selected bond lengths, heat of formation, first ionization potentials, and heat of isomerizations were detd. for the title systems. MNDO/2 ´ 2 CI calcns. show that the barrier of the isomerization I .dblharw. HC(S)C(S)H (IV) amts. to .apprx.36 kcal/mol relative to I and 24 kcal/mol relative to IV. The barrier is only slightly lowered if the symmetry of the transition structure is reduced from C2v to Cz by twisting the mol. about the S-S bond.
Formation and properties of N-arylthioaminyls. Fabian, Jurgen; Decker, Daniel; Mayer, Roland. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1988), 28(9), 325-6.
2,4,6-(Me3C)3C6H2SN.bul.C6H4R-4 (I, R = H, Me, OMe, CO2Et, Cl, Br) were prepd. by reaction by 2,4,6-(Me3C)3C6H2SCl with 4-RC6H4NH2 and PbO2 oxidn. of 2,4,6-(Me3C)3C6H2SNHC6H4R-4. Ab initio calcns. were performed on the mol. structure and S-N bond length of I.
Investigations on differentiation of wood species by infrared spectroscopy. Part 1. Wienhaus, Otto; Niemz, Peter; Fabian, Juergen. Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Holzforschung und Holzverwertung (1988), 40(6), 120-5.
IR spectra were interpreted for wood of spruce, pine, fir, black locust, larch, oak, red beech, willow, maple, and alder and IR spectra were given for several DMSO lignin samples. In selected spectral ranges, distinct differences were found between hard- and softwood, but differentiation between individual species was less feasible.
derivatives. XII. Fluorescence behavior of 4-aminomethylene-D2-pyrazoline-5-thiones. Freyer, Wolfgang; Teuchner, Klaus; Fabian,
Juergen. Zentralinst. Opt. Spektroskop., Dtsch. Akad. Wiss.,
The solvent effect on the UV, fluorescence, and Stokes shift in the title deriv. I was related to the difference in the dipole moments between the S0 and S2 states. Tautomerization in the excited state and MO calcns. of I in its S0 and S1 states are discussed.
A review with 171 refs. with emphasis on diradical structures for near-IR laser dyes.
Reaction of dithiocarbamates with nitrogen-containing derivates of oxalic acid. Fulop, Vilmos; Kalman, Alajos; Beckert, Rainer; Fabian, Juergen. Cent. Res. Inst. Chem., Hung. Acad. Sci., Budapest, Hung. Monatshefte fuer Chemie (1989), 120(6-7), 561-9.
Amidation of CS2 with primary arylamines in the presence of Et3NH in Et2O gave RNHC(S)S- Et3N+H [R = (un)substituted aryl] which on cyclocondensation with R1N:CClCCl:NR1 [R1 = (un)substituted aryl] in CHCl3 in the presence of Et3N gave 37-90% thioxobis(arylimino)thiazolidines I. The byproducts of the reaction are RNCS, R1NCS, and R1NHC(S)C(S)NHR1. The crystal structure of I (R = 4-MeOC6H4, R1 = Ph) was detd.
1-Amino-2-hydrazinopyrimidine N-ylides. Unusual tautomers of 1-aminopyrimidine 2-hydrazones. Liebscher, Juergen; Hassoun, Ahmed; Fabian, Juergen. Sekt. Chem., Humboldt-Univ. Berlin, Berlin, Ger. Dem. Rep. Monatshefte fuer Chemie (1989), 120(8-9), 749-58.
1-Amino-2-methylthiopyrimidinium iodides I [R = Ph, COPh, 4-O2NC6H4, 2,4-(O2N)2C6H3, Ac; R1 = Ph, 4-MeC6H4, 4-ClC6H4, 4-MeOC6H4] were prepd. by reaction of 3-isothiocyanato-2-propeniminium perchlorates with hydrazines and subsequent methylation of the resulting 1-amino-2(1H)-pyrimidinethiones. Reaction of I with hydrazine causes substitution of the methylthio group and results in the formation of deeply colored 1-amino-2-hydrazinopyrimidine N-ylides as unusual tautomers of the commonly expected 1-amino-2(1H)-pyrimidine hydrazones. The structure of these N-ylides was proved by spectroscopic methods as well as by subsequent transformation to 3-amino-1,2,4-triazole[2,3-a]pyrimidinium salts by dehydration or to pyrimidotriazinium salt by oxidn. Reaction of N,N-disubstituted 1-amino-2-methylthiopyrimidinium salt with hydrazine also causes substitution of methylthiol; the resulting orange N,N-disubstituted 1-amino-2(1H)-pyrimidine hydrazone, however, cannot tautomerize to N-ylides.
states of azo compounds: Strong pp* fluorescence of
The low-temp. absorption and luminescence of bis-4,4'-diethylaminoazobenzene (I) in 2-methyltetrahydrofuran were measured. On the basis of the spectral characteristics, this luminescence was interpreted as the fluorescence from the 1st excited singlet state (pp*). A comparison of the spectral and photophys. properties of I with those of other para-substituted trans-azobenzenes enables drawing some conclusions concerning the structure and fluorescence of these systems.
calculations on polymethines. XXV. The molecular and electronic structure of
3,3'-dimethyl-3,3'-pyridocyanines and related non-Kekule polymethine dyes. Fabian, J.. Sekt. Chem., Tech. Univ.
Dresden, Dresden, Ger. Dem. Rep.
Journal fuer Praktische Chemie (
Non-Kekule polymethines are polymethine dyes that cannot be written by single Kekule-type formulae. As demonstrated with 3,3'-dimethyl-3,3'-pyridocyanines (I) the electron distribution and term level ordering of them differ greatly from those of the related simple open-chain polymethines (streptopolymethines), considering the latter ones as constitutive elements of these dyes according to Daehne's polymethine concept. Non-Kekule dyes are, however, closely related to isoconjugated classical polymethine dyes. The peculiar features of the non-Kekule polymethines are well understood in terms of simple MO theory. Orbital tracing assisted by MOA (MO anal.) reveals crossing between the frontier orbitals of these dyes and those of the related open-chain polymethine substructures. Addnl. insight into peculiarities of I is gained at the semiempirical level by analyzing the p-electronic system in terms of the heterocyclic end groups and the interconnecting odd-alternant hydrocarbon (carbopolymethine) chain. Numerical predictions are made based on MNDO optimum geometries. According to CNDO/S and PPP calcns. the non-Kekule dyes considered absorb at longer wavelengths that the isoconjugate classical dyes. In the case of the first members of series I the lowest-energy transition is less detd. by the characteristic polymethinic charge redistribution inherent to polymethine dyes than by notable heterocycle-to-chain charge transfer (CT). The interfragmental CT upon excitation reduces the transition probability of this electronic transition. Some calcns. performed beyond the monoexcitation approxn. indicate a certain biradicaloid character of the non-Kekulean dye structures. The exceptional position of these dyes is also indicated by the higher heats of formation of I relative to the isomeric classical dyes.
more stable than 1,2-dithioglyoxal as evidenced by a combined experimental and
theoretical IR spectroscopic approach. Diehl, Frank; Meyer, Hermann; Schweig,
Armin; Hess, B. Andes, Jr.; Fabian, Juergen.
A matrix isolation IR spectrum of 1,2-dithiete has been obtained and compared with the computed (MP2/6-31G*) vibrational spectra of 1,2-dithiete and 1,2-dithioglyoxal. The results give further support to the interpretation of earlier photoelectron spectroscopic results that 1,2-dithiete is more stable than 1,2-dithioglyoxal.
Ab initio calculation of the vibrational spectrum of thioformaldehyde. Fabian, Juergen; Hess, Andes B., Jr. Sekt. Chem., Tech. Univ. Dresden, Dresden, Ger. Dem. Rep. Zeitschrift fuer Chemie (1990), 30(2), 65-6.
Vibrational frequencies of HCHS and DCDS, calcd. by the MP2 6-31G* method and cor. for anharmonicity, agreed well with exptl. data.
spectroscopic investigation of pyrimidine derivatives.
Nyulaszi, L.; Pasinszki, T.; Reffy, J.; Veszpremi, T.; Fabian, J.; Thiel, W.
Dep. Inorg. Chem., Tech. Univ.,
The HeI UPS spectra of acetamidine, perimidine, and four 2-substituted perimidine derivs. have been recorded and interpreted using ab initio and MNDO quantum-chem. calcns. A large interaction between the naphthalene and amidine fragment was concluded from the lowest ionization energy. The color-detg. band of these compds. is strongly affected by the intramol. charge-transfer transitions, which are of low energy because of the low ionization energy of the perimidine moiety.
Molecular structure and electronic excitation of 1,2-dithiete and of the isomeric dithials. Janoschek, Rudolf; Hess, Andes B., Jr.; Fabian, Juergen. Inst. Theor. Chem., Karl-Franzens-Univ., Graz, Austria. Zeitschrift fuer Chemie (1990), 30(5), 176-7.
The mol. structures and electronic excitation energies of cis- and trans-HSCCSH and 1,2-dithiete (I) were calcd. by the improved virtual orbital ab initio method. The lowest excited state of I is ps* and is considerably higher in energy than those of the dithials.
with light absorption in the near infrared. Fabian, J,.Inst.
Org. Chem. Farbenchem., Tech.
A review with 177 refs. covering electronic structure, nonradical compds., radical compds., and applications of the title laser dyes.
An ab initio study
of the structure and electronic spectrum of 1,2-dithiete and 1,2-dithiin.
Cimiraglia, Renzo; Fabian, Juergen; Hess, B.
The ground state geometries of 1,2-dithiete and 1,2-dithiin were optimized at both the Hartree-Fock and MP2 levels with the 6-31G* basis set. In contrast to 1,2-dithiete, 1,2-dithiin is nonplanar with C2 symmetry. Subsequent calcns. on the first excited singlet states of each mol. were carried out using the variation-perturbation CIPSI method, in order to elucidate the main features of the electronic absorption spectrum.
Structure and Properties. Tyutyulkov, Nikolai; Fabian, Jurgen; Mehlhorn, Achim;
Dietz, Fritz; Tadjer, Alia. (1991), 249
pp. Publisher: (St. Kliment Ohridski
absorbing dyes. Fabian, Juergen; Nakazumi, Hiroyuki; Matsuoka,
Masaru. Inst. Org. Chem. Farbenchem., Tech. Univ. Dresden,
Applications of near-IR absorbing dyes, near-IR chromophores, and structures of the dyes were reviewed with >350 refs.
Triplet formation in aminoanthraquinones and its importance for the catalytic fading of dye mixtures. Borst, H.-U.; Kelemen, J.; Fabian, J.; Nepras, M.; Kramer, H. E. A. Inst. Phys. Chem., Univ. Stuttgart, Pfaffenwaldring 55, Stuttgart, Germany. Journal of Photochemistry and Photobiology, A: Chemistry (1992), 69(1), 97-107.
The catalytic fading of yellow azo dyes in an admixt. with blue, red, or violet anthraquinone dyes is due to a type-II photo-oxygenation during which singlet O is produced by the anthraquinone dye in its triplet state. The triplet quantum yields (which are of decisive importance in the extent of catalytic fading) of all monoaminoanthraquinone and diaminoanthraquinone isomers (model compds. for tech. dyestuffs) are measured in PhMe. The rate consts. of the radiationless deactivation and of the triplet formation (kISC) are detd. from the fluorescence quantum yield, the fluorescence lifetime, and the triplet quantum yield. kISC Depend strongly on the position of the substituents and are related to the singlet-triplet sepn. energies of the excited singlet and triplet states (ES11-ET11).
Ab initio calculations on 1,2-dithiins and valence isomers. Mann, M.; Fabian, J. Technische Universitaet Dresden, Institut fuer Organische Chemie und Farbenchemie, Mommsenstrasse 13, Dresden, Germany. THEOCHEM (1995), 331(1-2), 51-61.
Ab initio MO calcns. were performed at the RHF and MP2 level with split valence basis sets. As recently shown for 1,2-dithietes, inclusion of f-functions has a noticeable effect on the isomerization energies of 1,2-dithiins to dithiones. The parent structure 1a has C2-symmetry and the energy barrier of inversion via the fully conjugated planar structure is rather low (5.7 and 8.3 kcal mol-1 at the RHF/6-31G* and at the MP2/6-31G* level, resp.). The MP2/6-31G* geometry of 1a is in line with the structural features revealed by X-ray anal. of some derivs. According to the theor. and exptl. data, the CSSC and CCCC dihedral angles of 1a are about 54° and 28°, resp. Whereas the parent compd. 1a is more stable by at least 15 kcal mol-1 with respect to the open chain dithiones at the MP2 level (with basis sets including d- and f-functions), some substituted dithiins are energetically not favored compared to the resp. isomeric dithiones. Thus dithiomaleinic and dithiofumaric amides are predicted to be more stable than 3,6-diamino-1,2-dithiin. In view of these results, the synthesis of 3,6-diamino-1,2-dithiins reported in the literature should be considered with caution. Substitution of the 3,6-positions by acceptor groups such as nitrile, however, favors the ring structure over the open chain structure. According to isodesmic reactions ("methyl stabilization energies"), cyano and amino substitution of the dithiin ring results in a stabilization of the ring by 9 and 32.5 kcal mol-1, resp. Because of the strong stabilization effect by the amino groups in the acyclic dithione, the bisthioamides are energetically favored.
Thioformaldehyde S-methylide as a reactive biradical. An ab initio quantum chemical study. Fabian, Juergen; Eckart, Udo; Hess, Andes B., Jr. Fak. Mathmatik Naturwiss., Tech. Univ. Dresden, Dresden, Germany. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (1995), 44(2), 99-105.
Mol. geometries, charge distributions, and spectral properties in the IR and UV range of the title compd. were modeled by the Hartree-Fock method and with post Hartree-Fock correlation methods. CAS-SCF calcns. based on multiconfiguration were drawn for comparison.
of molecular structure and spectra of HNS. Mehlhorn, Achim; Fabian, Juergen; Gabriel,
Wolfgang; Rosmus, Pavel. Fachbereich Chemie der Technischen Universitaet
Using complete active space SCF electronic wavefunctions the three-dimensional potential energy and elec. dipole functions for the lowest two singlet and triplet states of HNS have been generated and used for the evaluation of the spectroscopic consts., anharmonic frequencies and radiative transition probabilities. The electronic excitation energies have been calcd. by a multi-ref. CI approach.
Structures and properties of 1,2-dithiolylium-4-methide, 1,2-dithiolylium-4-olate and 1,2-dithiolylium-4-thiolate: an MO study at the HF and post-HF levels. Mann, Matthias; Fabian, Juergen. Inst. Organische Chemie, Technischen Univ. Dresden, Dresden, Germany. Journal of Physical Organic Chemistry (1995), 8(8), 536-44.
The mol. and electronic structures of the cyclic 1,2-dithiolium ylides (I; X = CH2, S, O) and their acyclic dithiocarbonyl valence isomers were studied by ab initio methods. All mol. structures were fully optimized at the R(U)HF/6-31G* and R(U)MP2/6-31G* levels of theory. The results of the restricted and UHF calcns. are less reliable since the RHF wave functions of the cyclic compds. proved to be singlet/triplet unstable. A marked ground-state energy depression occurs on passing from restricted to unrestricted HF methods. The title compds. are of diradicaloid nature and belong to the non-classical class of structures. The heterocycles are planar and display C2v symmetry, while the cisoid open-chain dithiocarbonyl isomers are slightly distorted (C2 symmetry). According to the calcd. bond lengths and charge distributions, the title compds. are in fact more or less zwitterionic. The thiolate is the most polar compd. of this series. According to RMP2 calcns., the thiolate and olate (I; X = S, O, resp.) should exist in the single ground rather than in the triplet state. However, in these cases the isomeric acyclic compds. are predicted to be almost isoenergetic with the cyclic compds. Since the cyclic ylides have higher dipole moments than the acyclic dithiocarbonyls, the ylides will gain stability in polar solvents. However, the continuum quantum chem. model used in estg. the solvent effect does not favor the ring compds. sufficiently to exclude valence isomerization between the ring-closed and ring-open compds.
quantum-chemical studies of the vibrational spectrum of dimethyl
K.; Fabian, J. Institut Analytische Chemie,
Technischen Universitaet Dresden,
Dresden, Germany. Zeitschrift
fuer Physikalische Chemie (
The vibrational spectrum of di-Me trithiocarbonate (1) has been reexamd. by a combined exptl. and theor. study at the correlated Hartree-Fock based ab initio quantum chem. level (RMP2/6-31G*) and at he level of d. functional theory (DFT) using the hybrid Becke 3-LYP functional. The theor. equil. geometries (re) are in excellent agreement with the exptl. ra geometries obtained by electron diffraction studies . DFT slightly overestimates bond lengths. The theor. frequencies of 1 enabled a crit. examn. of the former assignments of the 30 normal modes. Some frequencies at the low wavenumbers had to be reassigned. The wavenumbers of the CS-stretches differ from the exptl. data by 18 cm-1 on the av. The C = S frequency is more sensitive to the structure of the 18 cm-1 on the av. The C = S frequency is more sensitive to the structure of the conformers than expected by theory. The qual. agreement between theor. IR intensities and exptl. integral intensities is less satisfactory and is even more worse for Raman-intensities (calcns. at the RHF/6-31G* level of theory). Neither the inclusion of addnl. polarization functions nor of diffuse functions has removed this discrepancy [RHF/6-31G(d,f) and RHF/6-31 ++ G(2d), resp.]. Accordingly to the normal coordinates, most of the vibrations are less localized and cannot be labeled by a single descriptor. The C = S stretch, however, is of local nature in the main, whereas the residual CS stretches contain, at least, main components of the expected sym. or antisym. vibrational behavior. The syn,syn-conformer of 1 is slightly more stable than the syn,anti-conformer. According to calcns. in the self consistent reaction field (SCRF) at the RHF/6-31G* level, the energy difference between the conformers drops from 10 kJ/mol to about 3 kJ/mol on passing from the gas phase to a polar solvent. The presence of the two isomers is documented in the exptl. IR spectrum.
Molecular structure and electronic excitation of S-ylides and heteroanalogs. Fabian, Juergen. Inst. Organische Chemie, Technische Univ. Dresden, Dresden, Germany. Sulfur Letters (1995), 19(3), 93-100.
In order to reveal the mol. structure of the diradicaloid thioformaldehyde S-methide (1, X = S) and 3,4-dimethylenethiophene (2, X = S) and hetero analogs contg. oxygen or nitrogen calcns. have been performed by the d. functional theory (DFT) using Becke's 3-parameter functional and Pople's split valence basis sets. The calcns. provide very satisfactory results concerning mol. geometries but the energies for the single mols. are too low relative to those of the related triplet mols. In spite of the marked shifts of electron d. in the p-system, in accordance with the ylidic character of the compds. considered, the dipole moments with the ylidic character of the wavelength absorption of the ylides are surprisingly well reproduced by ab initio calcns. employing full CI of only singly excited states (CIS), based on DFT optimized geometries.
Theoretical study on O-, N- and S-ylidic photoisomers derived from phenylvinylethers, phenylvinylthioethers and phenylvinylamines. Fabian, Juergen; Wolff, Thomas. Institut fuer Organische Chemie, Technische Universitaet Dresden, Mommsenstrasse 13, D-01062, Dresden, Germany. Journal of Photochemistry and Photobiology, A: Chemistry (1996), 96(1-3), 1-5.
In order to reveal the nature of the primary short-lived photoproducts (Y) of phenylvinylethers, phenylvinylthioethers and phenylvinylamines and to rationalize their photophys. properties, quantum chem. calcns. were performed at the restricted and UHF (HF) level of theory and beyond employing split valence basis sets plus polarization functions. According to the population of the pv (and dv) orbitals within the Mulliken population anal., the non-classical compds. Y are ylidic with carbon-heteroatom bonds shortened with respect to those of compds. with a classical structure. The ylidic character, however, is lower than that calcd. for the formaldehyde methide, thioformaldehyde methide and azomethine methide parent compds. The long-wavelength absorptions are due to an allowed v®v* transition. They are satisfactorily reproduced by HF-based single CI (CIS) calcns. in spite of the well-known limitations of this approach. The S0/T1 splitting energies alter in the sequence O.apprx.S.mchlt.N. The inability to detect spectroscopically the triplet state 3Y* of the O- and S-ylidic photoproducts is probably due to the low S0/T1 gap of these compds.
Stabilization of sulfur imides. An ab initio theoretical study. Sperling, D.; Fabian, J.. Inst. fuer Organische Chemie, Tech. Univ. Dresden, Dresden, Germany. Sulfur Letters (1996), 19(5), 189-196.
In order to est. electronic stabilization effects of donor and acceptor substituents R on the sulfur imide (thionitroso) group (N=S) the isodesmic reaction of R-N=S with ammonia has been calcd. (aminyl stabilization energies). The calcns. have been performed at the RHF (RHF) level of theory and by gradient cor. d. functional theory (DFT) using the Becke3LYP functional. Pople's larger split valence basis set (6-31G*) was employed in both series of calcns. According to the RHF as well as DFT calcns. the N=S group is increasingly stabilized by donor substituents in the sequence Me<SMe<OMe<NH2<NMe2. The successful synthesis of two N-diorganyl sulfur imides by Middleton (1966) is in accordance with this conclusion. The effect of p-delocalizaiton is weak as demonstrated with vinyl and Ph substituted sulfur imides (C-centered thionitoso compds.). The trimethylsilyl substituent does not stabilize electronically but steric hindrance may impart the mol. kinetic stability. The change of the electron distribution at the N=S group in the series of substituted compds. reflects the energetic stabilization. The net charges have been derived by MPA (Mulliken population anal.) and by NPA (natural population anal.).
Ab initio MO
calculations on 1,2-dithietes and valence isomers. Mann, Matthias; Fabian, Juergen. Inst. Organische
The valence isomerization of the 1,2-dithiete parent compd. to the open-chain dithial was studied by CASSCF multiconfiguration methods including the CASPT2 perturbational treatment. The isomerization energy remains small at the highest level of theory. In agreement with Jonas and Frenking, the cyclic structure is only then preferred over the acyclic ones if f-functions on the sulfur atoms are considered. If they are included, the 1,2-dithiete is more stabler by 3.8 kcal/mol and the barrier amts. to 24.9 kcal/mol at the CASPT2(8,8)/6-31G(2df)//MP2/6-31G* level of theory. According to MP2/6-31G* geometry optimizations, substitution of H by NH2 and CH3 reduces the stability of the 1,2-dithiete ring structures relative to the open-chain dithiocarbonyl structures, whereas the inverse holds for acceptor substitution by CN and CF3. A higher stability of benzodithiete relative to ortho-dithiobenzoquinone is predicted at all employed levels of theory. This is in good agreement with conclusions drawn from exptl. results. Whereas the exptl. microwave geometry of 1,2-dithiete is well reproduced theor., the exptl. electron diffraction geometry of 3,4-bis-(trifluoromethyl)-1,2-dithiete differs from the calcd. one.
Theoretical study of pericyclic reactions of nitrosoethylene and (thionitroso)ethylene. Sperling, Dirk; Mehlhorn, Achim; Reissig, Hans-Ulrich; Fabian, Juergen. Institut Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. Liebigs Annalen (1996), (10), 1615-1621.
Structure and reactivity of the title compds. were examd. by ab initio methods at the post Hartree-Fock level of theory. Both compds. are expected to undergo electrocyclic ring closure to 4H-1,2-oxazete and 4H-1,2-thiazete, resp. The alternative electrocyclic reaction affording 2H-azirine 1-oxide and 2H-azirine 1-thioxide is less favored. (Thionitroso)ethylene is more reactive than the O-contg. congener. The same holds for the cycloaddn. reaction with ethylene. [4+2] Hetero Diels-Alder reactions furnishing 4H-1,2-oxazine or 4H-1,2-thiazine are favored over the [3+2] cycloaddn. reactions providing 2H-pyrrole 1-oxide and 2H-pyrrole 1-thioxide. The results of RMP2/6-31G* calcns. and results obtained at lower levels of theory are compared and discussed with respect to the exptl. material available. Addnl. single-point calcns. at the computationally more demanding QCISD/6-31G* level confirmed conclusions drawn from RMP2 calcns. Test calcns. also showed that the theor. results are less affected by consideration of the temp. by statistic thermodn. and by inclusion of solvent effects by a self-consistent reaction-field method.
A density functional study of hyperfine structures of neutral S,N-heterocycles. Gassmann, J.; Fabian, J. Institut Organische Chemie, Technische Univ. Dresden, Dresden, Germany. Magnetic Resonance in Chemistry (1996), 34(11), 913-920.
The electronic structures and isotropic hyperfine coupling consts. of a series of neutral radicals consisting of ten S,N-heterocyclic compds. were investigated by means of d. functional theory (DFT). The mol. geometries were optimized by gradient cor. DFT (UB3LYP) methods and isotropic hyperfine coupling consts. (hfccs) were calcd. through the Fermi contact anal. The basis sets were 6-31G(d) and TZVP. The hfcc values were compared with exptl. data and with theor. results obtained by semi-empirical quantum chem. calcns. (AM1/UHF and INDO/UHF) and by ab initio quantum chem. calcns. (UMP2, UMP3 and UMP4). The results from DFT are highly superior to those of the semi-empirical methods. As shown for 1,3,2-thiadiazolyl, the computationally more demanding ab initio calcns. do not provide better results with the same basis sets.
DFT- and post-HF-study on structure and electronic excitation of acyclic and cyclic sulfur diimides. Strassner, Thomas; Fabian, Juergen. Institut fur Organische Chemie der Technischen Universitat Dresden, Dresden, Germany. Journal of Physical Organic Chemistry (1997), 10(1), 33-41.
A series of representative org. acyclic and cyclic sulfur diimides were studied by Hartree-Fock-plus-correlation ab initio quantum chem. and by d. functional theory using Becke's three-parameter functional along with the LYP functional. The widely used formula representation -N=S=N- for these compds. suggests octet expansion of sulfur. This is not confirmed by theory. Although d-polarization functions significantly improve the numerical results, sulfur d-orbitals are hardly occupied. The calcd. electronic charge distribution derived by population anal. and by the atoms-in-mols. topol. theory favors charge sepn. resulting in a more or less ylidic structure with -N=S+-N-- and -N-=S+-N- resonance contributors. This structure does not exclude relatively short SN bond lengths. The characteristics of the bonds in the parent structures is preserved in some non-Kekule-type NSN heterocycles. Strong SN bond charge sepns. of organyl sulfur diimides are accompanied by short SN bond distances and narrow S0/T1 and S0/S1 energy gaps. The exptl. well known naphtho[1,8-cd][1,2,6]thiadiazine and the unknown 3,4-dimethylene-1,2,5-thiadiozole belong to this series. The calcns. confirm that 1,2,3-thiadiazole is the diaza analog of thiophene rather than the vinylene-bridged sulfur diimide, while more complex heterocycles such as benzo[1,2-c; 4,5-c']bis[1,2,5]thiadiazole take an intermediate position between classical and non-classical structures. Two closely related min. structures are defined on the DFT Born-Oppenheimer energy surface of naphtho[1,8-cd; 4,5-c'd']bis[1,2,6]thiadiazine, but so far only one compd. is exptl. known. The lowest energy structure is the quinoid form corresponding to the exptl. known compd.
interaction in some supramolecular organic structures. Rauwolf, Cordula; Fabian, Jurgen; Mehlhorn,
Achim. Fakultat Mathematik Naturwissenschaften, Technische Universitat Dresden,
Dresden, Germany. Wissenschaftliche
Zeitschrift der Technischen Universitaet
Structures and binding energies of macrocyclic compds. composed of tetracationic paraquat or neutral crown ether host mols. and benzene, substituted benzenes or the dicationic paraquat guest mols. calcd. by semiempirical PM3 calcns. are reported. The calcd. structures of the resulting inclusion compds. and of interlocked catenanes are, in principle, correct. Calcd. binding energies are relatively high for the tetracatonic supermols. Attempts were also made to est. binding energies of donor-acceptor complexes by d. functional theory with gradient-cor. B3LYP exchange-correlation functionals. The complexes consist of planar or nearly planar compds. such as tetrathiafulvalene as donor and tetracyanoethylene as acceptor mols. Only few information is available from 'wet chem.' expts. suggesting that the calcd. binding energies of the 'isolated' supermols. are underestd.
l4s2-Sulfur Heterocycles. An ab Initio and Density Functional Study. Fabian, Juergen; Hess, B. Andes, Jr. Institut fuer Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. Journal of Organic Chemistry (1997), 62(6), 1766-1774.
In order to better understand the structure and properties of 2l-thioallyl (alternatively named 2-thiapropanediyl or thioformaldehyde S-methide) and the heterocyclic derivs. 3,4-dimethylenethiophene, naphtho[1,8-c,d]thiopyran, thieno[3,4-c]thiophene, and thieno[3,4-f]benzo[c]thionaphthene ab initio quantum chem. and d. functional theory were utilized. The general conclusions drawn from the distinctly different approaches are the same. The low d-orbital occupation is not compatible with any hypervalency of sulfur including d-valence orbitals. Rather, the structures may be understood as ylidic ones with Coulombic CS-bond contraction, and as indicated by low singlet/triplet (S0/T1) splitting energies, the structures are more or less diradicaloid as well. The mol. geometries calcd. at the MP2 and DFT/Becke3LYP level of theory are very similar with CS bond lengths between 1.64 and 1.70 .ANG. for the nonclassical structures. The ionization energies are relatively low. For the sake of comparison the quinoid structures benzo[c]thiophene, acenaphtheno[5,6-cd]thiopyran and naphtho[1,8-c,d;5,4-c'd']dithiopyran were included in the study. They proved to be borderline cases between compds. of nonclassical and classical structure. According to the calcd. mol. geometry and the charge distribution acenaphtheno[5,6-cd]thiopyran has a nonclassical structure.
A theoretical study of some non-classical organic compounds with di-coordinated sulfur. Fabian, J.. Inst. Org. Chem., Technische Univ. Dresden, Dresden, Germany. THEOCHEM (1997), 398-399, 411-416.
A series of di-coordinated sulfur org. compds. on non-classical structure contg. the C=S=C, C=S=S or N=S=N group has been studied by post-Hartree-Fock (MP2, QCISD and QCISD(T)) and multiconfiguration methods (CASSCF, CASPT2). The calcd. structures exhibit relatively short bonds to the central sulfur atom along with strong charge sepns. of these bonds (ylidic structures). The diradicaloid nature of the non-classical structures is indicated by low S0/T1 energy gaps. The parent compd. 2l4-thioallyl (thioformaldehyde S-methylide, 1) and the most simple thiosulfine (thioformaldehyde S-sulfide, 4) undergo conrotatory electrocyclic ring closure to the energetically favored thiirane and dithiirane, resp. The reaction is less exothermic and the energy barrier is higher for 4 than for 1. The 1,3-dipolar cycloaddn. of 1 to ethylene is more exothermic than the reaction of butadiene to ethylene. The calcd. energy of activation of the concerted cycloaddn. of 1 amts. to only 8 kcal mol-1. Similar to the prototype Diels-Alder reaction, the concerted reaction of 1 is about 10 kcal mol-1 and is favored over the non-concerted stepwise reaction.
Quantum-chemical calculations of the reactivity. Isomerization of some substituted cyclopropanes. Sperling, Dirk; Reissig, Hans Ulrich; Fabian, Jurgen. Institut Organische Chemie, TU Dresden, Dresden, Germany. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (1997), 46(5), 33-38.
Cis-1-vinyl-, -1-formyl-, -1-thioformyl-, and -1-iminomethyl-2-vinylcyclopropane undergo isomerization to 1,4-cycloheptadiene, 2,5-dihydrooxepine, 2,5-dihydrothiepine, and 2,5-dihydroazepine, resp. The results of d. functional theory (B3LYP/6-31G*) and single-point ab initio calcns. (MP2/6-31G*//B3LYP/6-31G*) are in good agreement with expt. The isomerization of 1-vinyl-2-thioformyl- and 1-vinyl-2-iminyl-substituted cyclopropanes is predicted to be exothermic with reaction heats of .apprx.13 and 11 kcal/mol and barriers to isomerization of .apprx.8 and 20 kcal/mol, resp. As shown for the isomerization of cis-1-vinyl-2-formylcyclopropane to 2,5-dihydrooxepin, consideration of the solvent effect and correction by statistical thermodn. do not affect the isomerization energies significantly. The nature of the transition structures considered is discussed. They strongly resemble those of Cope and Claisen rearrangements. Bond formation and cleavage occurs simultaneously and the stabilization of the transition structure is discussed in terms of delocalized structures.
Five-ring cycloamidines. Deeply colored heterocycles with unusual properties. Part 2. Molecular- and electronic structure. Fabian, Juergen; Goerls, Helmar; Beckert, Rainer; Atzrodt, Jens. Institut Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. Journal fuer Praktische Chemie/Chemiker-Zeitung (1997), 339(8), 735-741.
The crystal and mol. structure of two N,N'-aryl-5-aminoimidazol-4-imides was detected by x-ray anal. The structural parameters are discussed in conjunction with theor. data obtained by d. functional and ab initio quantum theory. The interpretation of the mol. structures derived from x-ray diffraction is made more difficult by statistic disorder or by enclosure of H2O in the crystal. Theory predicts a planar 5-aminoimidazol-4-imide parent structure with an energy barrier to H-transfer of .apprx.25 kcal/mol [DFT RB3LYP/6-311+G** and ab initio G2(MP2)]. The CC bond of the 5-membered ring is exceedingly long. CC-bond length elongation is also reported for oxalbisamidine. The structure of the parent compd. is discussed in terms of polymethinic and antiarom. substructures. Weinholds's natural bond orbital (NBO) scheme and natural resonance theory (NRT) as well as Schleyer's criterion of the nucleus independent chem. shift (NICS) is consulted to reveal the very nature of the unique bond system.
cycloamidines. Deeply colored heterocycles with unusual properties. Part 1.
Synthesis and spectral features. Atzrodt, Jens; Brandenburg, Joerg;
Kaepplinger, Christian; Beckert, Rainer; Guenther, Wolfgang; Goerls, Helmar;
Fabian, Juergen. Institut Organische Makromolekulare Chemie,
The cycloacylation reaction of benzamidines with oxalate-derived bisimidoyl chlorides such as (RC6H4N:CCl)2 (R = H, 4-Me, 4-NO2, 4-Me2N, 3-CF3) was investigated. For example, cycloacylation of benzamidine gives the corresponding 4H-imidazoles I in yields £92%. Because of rapid H-transfer processes in soln., the NMR of the 4H-imidazoles shows only a single signal set. Apart from prototropism, I (R = 4-Me) shows interesting properties as an amphoteric heterocycle. The protonation of I (R = 4-Me) is accompanied by a change of color from orange to blue. Probably, protonation takes place on the exocyclic imino N to give a cyanine type chromophore. The resulting cation can also be regarded as an antiarom. 1,3-diazacyclopentadienylium system. To investigate the influence of exocyclic substituents at N on the UV/vis absorption, appropriate compds. were synthesized. Whereas electron-withdrawing groups cause hypsochromic shifts of the first UV/vis absorption band, the Me2N group shifts this band bathochromically as exemplified by I (R = 4-Me2N). This novel cycloamidine shows strong acidochromism with bathochromic shifts >150 nm.
A DFT study on the vinylcyclopropanecarbaldehyde to 2,5-dihydrooxepin hetero-Cope-type rearrangement and on related reactions. Sperling, Dirk; Reissig, Hans Ulrich; Fabian, Juergen. Institut Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. Liebigs Annalen/Recueil (1997), (12), 2443-2449.
The prototypical cis-2-vinylcyclopropanaldehyde (I) to 2,5-dihydrooxepin hetero-Cope-type rearrangement was studied by "exact" first-principle methods. The reaction pathway was examd. The reaction, as well activation energies, was calcd. for the unimol. transformation of I and various derivs. The derivs. differ from I by replacement of the CHO by the CH:S or CH:NH group and, in part, by replacement of H atoms at the substituted C atoms of the cyclopropane ring by OH or CHO substituents. The exptl. reaction parameters of I are surprisingly well reproduced by B3LYP/6-31G* d. functional and MP2/6-31G* ab-initio quantum theor. calcns. Reactant and product are nearly isoenergetic, while the activation energy amts. to .apprx.25 kcal/mol. In the case of the N- and S-contg. compds. the isomeric 7-membered ring structures are considerably favored over the cyclopropanes. Due to a low calcd. activation energy, a rapid formation of the 2,5-dihydrothiepin is expected. Substitution of the H at the substituted ring C atoms in I by OH and CHO also lowers the barrier and increases, in general, the exothermicity of the reaction. As shown by the reaction energies of isodesmic reactions, both reactants and products are stabilized by substitution. However, the 7-membered ring compds. are more stabilized than the cyclopropanes. The OH group exerts a different effect depending on whether the linkage is geminal or vicinal to the C:X group. The difference is caused by H-bond formation in geminal arrangements. The substituent effects in the cyclopropane series parallel those for the prototypical Cope- and Claisen-type series. The particular feature of the cyclopropane series is the lower stability of the cyclopropanes relative to the corresponding open-chain congeners. This is obviously due to the ring strain which over-compensates for attractive interactions between cyclopropane and the substituents. Thus, the formation of 7-membered ring compds. proceeds more easily than the formation of the corresponding compds.
in related Cope rearrangements.
Post-Hartree-Fock MP2 and density functional theory derived structure and vibrations of 1,2-dithiole-2-thione and 1,2-dithiol-3-one. Fabian, J.; Herzog, K. Institut fur Organische Chemie, Technischen Universitat Dresden, Dresden, Germany. Vibrational Spectroscopy (1998), 16(1), 77-83.
Post-Hartree-Fock MP2 and d. functional theory (DFT) calcns. with the combined B3LYP functional using the 6-31G(d) basis set were carried out to investigate structure and vibrational spectra of 3H-1,2-dithiole-3-thione and 3H-1,2-dithiol-3-one. Theory predicts planar structures of Cs symmetry in both cases. The geometric parameters and the results of the Natural Bond Orbital (NBO) and Natural Resonance Theory (NRT) calcns. are compatible with structures with localized rather than delocalized bonds. Schleyer's Nuclear Independent Chem. Shielding (NICS) criterion also indicates relatively low modes and their assignment. Uniformly scaled DFT frequencies reproduce the exptl. data in CCl4 and CS2 solns. not as well as uniformly scaled MP2 frequencies. The extension of the std. basis set of DFT calcns. from 6-31G(d) to 6-311 + G(2df,wp) affects vibrational frequencies and intensities to a minor extent.
thiosulfine-dithiirane-dithioester manifold R1R2(CS2). Fabian,
Juergen; Senning, Alexander. Inst. Organische Chemie, TU Dresden,
A review with 66 refs. describing the thiosulfine-dithiirane-dithioester manifold (TDDM) in detail, based on both theor. and exptl. findings, and its implications for synthetic org. chem. discussed. Results of numerous new quantum chem. calcns. obtained at the hybrid HF/DFT and beyond-HF ab initio level are reported, focusing particular attention upon the structure and the properties of thiosulfines.
Binding energies of organic charge-transfer complexes calculated by first-principles methods. Rauwolf, Cordula; Mehlhorn, Achim; Fabian, Jurgen. Inst. Org. Chem., Technische Univ. Dresden, Dresden, Germany. Collection of Czechoslovak Chemical Communications (1998), 63(8), 1223-1244.
Weak interactions between org. donor and acceptor mols. resulting in cofacially-stacked aggregates ("CT complexes") were studied by second-order many-body perturbation theory (MP2) and by gradient-cor. hybrid Hartree-Fock/d. functional theory (B3LYP exchange-correlation functional). The complexes consist of tetrathiafulvalene (TTF) and related compds. and tetracyanoethylene (TCNE). D. functional theory (DFT) and MP2 mol. equil. geometries of the component structures are calcd. by means of 6-31G*, 6-31G*(0.25), 6-31++G**, 6-31++G(3df,2p) and 6-311G** basis sets. Reliable mol. geometries are obtained for the donor and acceptor compds. considered. The geometries of the compds. were kept frozen in optimizing aggregate structures with respect to the intermol. distance. The basis set superposition error (BSSE) was considered (counterpoise correction). According to the DFT and MP2 calcns. laterally-displaced stacks are more stable than vertical stacks. The charge transfer from the donor to the acceptor is small in the ground state of the isolated complexes. The cp-cor. binding energies of TTF/TCNE amt. to -1.7 and -6.3 kcal/mol at the DFT(B3LYP) and MP2(frozen) level of theory, resp. (6-13G* basis set). Larger binding energies were obtained by Hobza's 6-31G*(0.25) basis set. The larger MP2 binding energies suggest that the dispersion energy is underestimated or not considered by the B3LYP functional. The energy increases when S in TTF/TCNE is replaced by O or NH but decreases with substitution by Se. The charge-transferred complexes in the triplet state are favored in the vertical arrangement. Self-consistent-reaction-field (SCRF) calcns. predicted a gain in binding energy with solvation for the ground-state complex. The ground-state charge transfer between the components is increased up to 0.8 e in polar solvents.
Molecular orbital modeling of solvent effects on excited states of organic molecules. Mora-Diez, N.; Montero, L. A.; Fabian, J. Laboratorio de Quimica Computacional y Teorica, Facultad de Quimica, Universidad de La Habana, Havana, Cuba. THEOCHEM (1998), 453 49-57.
The excited states of org. mols. are considerably affected in most cases by their environment. A simple example of this phenomenon is the blue-shift effect shown by np* bands upon increasing solvent polarity. The solvent effect on the excited states of furfural and 1-(N-methylpyridyl)-2-(p-quinoyl)ethylene (stilbazonium), were simulated by creating a set of clusters solute-(solvent)n compounded by distributing solvent mols. around the solute at random. These clusters were subsequently optimized using the semiempirical PM3 method to explore such a multiple-min. hypersurface of the supermol. system. The min.-energy sets of each system were selected for the calcn. of excited states by the CNDOL method combined with a procedure for singly excited CI.
Post-Hartree-Fock MP2 and density functional theory derived structure and vibrations of 1,2-dithiole-2-thione and 1,2-dithiol-3-one. Fabian, J.; Herzog, K. Institut fur Organische Chemie, Technischen Universitat Dresden, Dresden, Germany. Vibrational Spectroscopy (1998), 16(1), 77-83.
Post-Hartree-Fock MP2 and d. functional theory (DFT) calcns. with the combined B3LYP functional using the 6-31G(d) basis set were carried out to investigate structure and vibrational spectra of 3H-1,2-dithiole-3-thione and 3H-1,2-dithiol-3-one. Theory predicts planar structures of Cs symmetry in both cases. The geometric parameters and the results of the Natural Bond Orbital (NBO) and Natural Resonance Theory (NRT) calcns. are compatible with structures with localized rather than delocalized bonds. Schleyer's Nuclear Independent Chem. Shielding (NICS) criterion also indicates relatively low modes and their assignment. Uniformly scaled DFT frequencies reproduce the exptl. data in CCl4 and CS2 solns. not as well as uniformly scaled MP2 frequencies. The extension of the std. basis set of DFT calcns. from 6-31G(d) to 6-311 + G(2df,wp) affects vibrational frequencies and intensities to a minor extent.
Allene Oxide, Oxyallyl, and Cyclopropanone. Hess, B.
A detailed theor. study of the rearrangement of allene oxide (I) to cyclopropanone (II), the racemization of substituted II, and the isomerization of substituted II is presented. I rearrangement to II proceeded in a stepwise fashion in which I is first converted to oxyallyl via a newly found transition structure with subsequent ring closure of the oxyallyl to give II. A previously found transition structure is on the pathway that results in the racemization of chiral-substituted II. A new transition structure was also located that accounts for the previously obsd. conversion of cis-2,3-di-tert-butylcyclopropanone to its trans diastereomer. The discussion is based on the results of DFT and CASSCF methods. IRC calcns. were carried out for all transition structures located. Single-point energies were calcd. with the CASPT2N, QCISD(T), and UQCISD(T) methods. Good agreement was found between the calcd. results and those available from expt.
The structure of 3,4-diaza-1,6,6al4-trithiapentalenes- a combined experimental and theoretical study. Fabian, J.; Gloe, K.; Wust, M.; Kruger-Rambusch, T.; Rademacher, O.; Graubaum, H. Technische Universitat Dresden Institut fur Organische Chemie, Dresden, Germany. Phosphorus, Sulfur and Silicon and the Related Elements (1998), 140 35-52.
The x-ray structure of 2,5-bis(piperidyl)-3,4-diaza-1,6,6al4-trithiapentalene (1, R = piperidyl) is reported and compared with the equil. geometries calcd. for the diamino-substituted compd. by d. functional theory (B3LYP exchange-correlation functional). The mol. geometry and electronic structure of the 3,4-diaza-1,6,6al4-trithiapentalene parent compd. (1, R = H) has been examd. in more detail in conjunction with the nitrogen-free 1,6,6al4-trithiapentalene (2, R = H). Whereas Hartree-Fock-calcns. predict 1 and 2 as valence isomers in equil., DFT(B3LYP) as well as ab initio MP2 calcns. result in a single min. structures of C2v-symmetry. Substitution of methine groups by aza nitrogen in the 3- and 4-positions and introduction of amino groups in the 2- and 5-positions of 1,6,6al4-trithiapentalene (2, R = H) stabilize the heterocyclic compd. by formation of a polymethine-type substructure. According to DFT calcns. the C2v-symmetry is retained in passing from 1 (R = H) to the amino-substituted compd. (1, R = NH2). The nucleus-independent chem. shifts (NICS) of the five-membered rings of 3,4-diaza-1,6,6al4-trithiapentalene and of its nitrogen-free congener exhibit arom. bond delocalization.
Substituent effects on the vinylcyclopropane-cyclopentene rearrangement. A theoretical study by restricted and unrestricted density functional theory. Sperling, Dirk; Fabian, Juergen. Institut Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. European Journal of Organic Chemistry (1999), (1), 215-220.
The effect of donor substitution by the hydroxy group and of acceptor substitution by the cyano group on the activation energies of the vinylcyclopropane-cyclopentene rearrangement was calcd. by the spin-restricted RB3LYP/6-31G* method for reactant structures and by the spin-unrestricted UB3LYP/6-31G* method for transition structures. The activation energies of the rearrangement of hydroxy- and cyano-substituted vinylcyclopropanes are very similar for substitution in the same position. In agreement with earlier findings the substituent effects on the activation energies are closely connected with the radical stabilizing properties of the substituents. As indicated by singlet/triplet splitting energies, the transition structures are essentially biradicaloid. In spite of spin pairing in the transition structure the substituent effects on bond lengths and on stabilization energies are very similar to those of the free radicals corresponding to the 2 radical substructures. Thus, the transition structures may be considered, in good approxn., as structures consisting of 2 weakly interacting radicals.
calculations on S-centered 1,3-dipoles. 2. Reactivity of thiocarbonyl S-imides
in pericyclic reactions. Mloston, G.; Fabian, J. Department of Organic and
of high level quantum chem. calcns. on thiocarbonyl S-imides are reported. The reactivity of thioformaldehyde S-imide
Quantum chemical calculations on S-centered 1,3-dipoles. 1. Molecular and electronic structures of thiocarbonyl S-imides. Fabian, J.; Mloston, G. Technische Universitat Dresden, Institut fur Organische Chemie, Dresden, Germany. Polish Journal of Chemistry (1999), 73(4), 669-681.
of high-level quantum-chem. calcns. on thiocarbonyl S-imides RR1C:S+NR2 are
reported. Structure and properties of
thioformaldehyde S-imide (I) (CH2:
monothioacetylacetone. A combined ab initio and density functional study. Fischer, G.; Fabian, J.. Inst. Organische
Chem., Technische Univ. Dresden, Dresden, Germany. Zeitschrift fuer
Physikalische Chemie (
Correlation-cor. ab initio calcns. using the G2(MP2) method and d. functional calcns. using a generalized gradient hybrid HF/DF method (RB3LYP) were performed to discuss structure and properties of the chelated enol and enethiol tautomers of monothioacetylacetone and, for comparison, the chelated enol tautomer of acetylacetone. According to the calcns. the 2 S-contg. tautomers are nearly equal in energy. The chelated all-cis-4-hydroxy-3-pentene-2-thione (Z-enol) is »1 kcal/mol lower in energy than the all-cis-4-mercapto-3-penten-2-one (Z-enethiol) and therefore predominating in the chem. equil. The Z-enol also shows the stronger bond delocalization in the mol. backbone and the more efficient H bond (resonance-assisted H bonding). The barrier height of the enol-to-enethiol tautomerization was calcd. to <10 kcal/mol. Therefore, interconversion between the protropic tautomers will take place rapidly. The calcd. mol. geometries and the energetics are in good agreement with the exptl. results available. The electronic structure of the tautomers and the H bonding are discussed in terms of at. charges and bond parameters as well as in terms of 2nd-order stabilization energies obtained by natural bond orbital anal. and natural resonance theory. The nucleus-independent chem. shifts (NICS) of the ring-shaped chelated tautomers and of the interconversion transition structures exclude cyclic bond delocalization (aromaticity). The compds. rather exhibit features of the open-chain merotrimethine structure.
rearrangements of divinylcyclopropane derivatives and hetero analogs in
competition with Cope-type rearrangements. A DFT study.
Sperling, Dirk; Reissig, Hans-Ulrich; Fabian, Jurgen. Institut Organische
Two possible types of competing [1,3] rearrangements of divinylcyclopropane derivs. and of the hetero-analogous compds. vinylcyclopropanecarbaldehyde and vinylcyclopropanecarbthioaldehyde to 5-membered ring compds. were investigated theor. by (U)DFT (Becke3LYP/ 6-31G*) methodol. Although both of the rearrangement pathways correspond to a reaction of the monosubstituted cyclopropane substructure, i.e. a reaction of vinylcyclopropane or of cyclopropanecarb(thio)aldehyde, new features in the reactivity are seen due to the combination of 2 substituents. Reaction parameters such as reaction and activation energies of the [1,3]-sigmatropic rearrangements were calcd. and compared. Substituent effects of hydroxy and formyl (donor and acceptor) groups in specific positions were also considered. On the basis of these calcns., the [1,3] rearrangement of vinylcyclopropanecarbaldehydes to dihydrofurans can be expected to be kinetically favored over their conversion to cyclopentenes, while formation of the latter should be favored thermodynamically. This prediction is borne out by the exptl. findings. Depending on the substitution pattern, the [1,3]-sigmatropic rearrangement of vinylcyclopropanecarbaldehydes may compete with the [3,3]-sigmatropic rearrangement. For the other investigated structures, the [1,3] rearrangement is strongly disfavored.
Single configuration interaction study on conjugated betainic chromophores based on DFT optimized geometries. Fabian, J.; Rosquete, G. A.; Montero-Cabrera, L. A. Technische Universitat Dresden, Institut fuer Organische Chemie, Dresden, Germany. THEOCHEM (1999), 469, 163-176.
The structure of a series of heterocyclic betaines was calcd. by d. functional theory (DFT) methods. The charge distribution and bond characteristics of these compds. were analyzed by Weinhold's natural bond orbital anal. (NBO) and by natural resonance theory (NRT). In order to probe the arom. character of the ring fragments, Schleyer's nucleus-independent chem. shifts (NICSs) were calcd. by GIAO-RHF. Ab initio single CI calcns. (SCI) correctly predict intense p ® p* transitions at low energies, but the transition energies of the color bands are overestd. Torsion around the interfragmental bond increases the charge sepn. between the mol. fragments and the dipole moment. The mol. fragments become increasingly arom. The absorption wavelengths increase on torsion while the oscillator strengths decrease.
Structure and spectral properties of the pentamethine merocyanine 5-(dimethylamino)pentadienal in solution. A combined DFT-SCI-SCRF study. Rosquete, Giselle A.; Fabian, Jurgen. Institut Organische Chemie, Technische Univ. Dresden, Dresden, Germany. Journal fuer Praktische Chemie (Weinheim, Germany) (1999), 341(7), 631-638.
To est. the solvent effect on mol. structure and on NMR and UV spectral data of 5-(dimethylamino)penta-2,4-dienal (I) the compd. was calcd. by 1st-principles methods. D. functional theory was employed for structural optimization with solvent effects simulated by the recently refined COSMO continuum model. According to the calcns. the mol. structure of I is noticeably affected by polar solvents resulting in a reduced bond length alternation. The relaxation of the mol. geometry in polar solvents is clearly reflected in the calcd. 13C NMR chem. shifts calcd. by GIAO-DFT and in the absorption wave nos. of the intense lowest-energy electronic transition calcd. by SCI. Although the optimum geometry of the solute mol. in the solvents was calcd. the magnitude of the solvatochromic shift is underestimated. The calcd. solvatochromic effect in water is enhanced if the specific solvent-solute interactions are considered by addn. of one water mol. to I in the solvent cavity.
Thiocumulenes (S-centered 1,3-dipoles)- a theoretical view. Fabian, Jurgen. Institut fur Organische Chemie der Technische Universitat Dresden, Dresden, Germany. Phosphorus, Sulfur and Silicon and the Related Elements (1999), 153-154, 357-358.
Symposium proceedings. Structure and reactions parameters of sulfines were calcd. by DFT at the B3LYP/6-311+G(3df) and by ab initio methods at the G2(MP2) level of theory.
On electronic structure and electronically excited states of sulfines (thione S-oxides). Petiau, Maxime; Fabian, Jurgen; Rosmus, Pavel. Institut fur Organische Chemie der Technischen Universitat Dresden, Dresden, Germany. Physical Chemistry Chemical Physics (1999), 1(24), 5547-5554.
The two lowest-energy n ® p* and p ® p* type transitions of the parent sulfine were predicted at different levels of theory, such as CASSCF/CASPT2, EOM-CCSD, CIS, TD-HF and TD-DFT. While calcns. by singles-only CI (CIS) and by RPA (TD-HF) methods provided too large transition energies, results obtained by time-dependent d.-functional theory (TD-DFT) are close to those of the multiconfigurational CASPT2 method. To characterize the sulfine chromophore, the sulfines of thiopropanal, thioacetone, 2,2,4,4-tetramethyl-3-thioxocyclobutanone, thioadamantanone, thiocyclopropenone, thiocyclopentadienone, thiocyloheptatrienone, 4,4'-dimethylthiobenzophenone and thiofluorenone were calcd. by the TD-DFT method. In good agreement with the exptl. findings the aliph. compds. absorb light intensively between 250 and 270 nm in the near-UV region due to p ® p* transitions. The exptl. known first intense higher-energy absorption bands of 4,4'-dimethylthiobenzophenone and thiofluorenone sulfines are also well reproduced by TD-DFT.
carbenium ion and an a-disulfide carbenium ion: a comparative molecular
orbital study. Langler, Richard Francis; Sung, Gabriel Carl
Yan; Fabian, Juergen. Department of Chemistry,
MeSCH2Cl undergoes hydrolysis under SN1 conditions 6800 times faster than MeSSCH2Cl. The results of 1st-principles quantum-chem. calcns. do not support earlier explanations for the superior facility of formation of the a-sulfide carbenium ion. The computational results are better understood in terms of delocalization and Coulombic effects.
Density functional derived structures and molecular properties of nickel dithiolenes and related complexes. Lauterbach, Christa; Fabian, Jurgen. Institut Organische Chemie, Technische Univ. Dresden, Dresden, Germany. European Journal of Inorganic Chemistry (1999), (11), 1995-2004.
mol. and electronic structure of the planar Ni dithiolene and of related
complexes derived from Ni dithiolene (I) by replacement of Ni by Pd or by Pt or
by replacement of S by NH (Ni diiminolene), O (Ni dioxylene) or Se (Ni
diselenolene), were studied by d. functional theory using the B3LYP functional
and the valence triple-zeta basis set 6-311+G* for all atoms except Pd and
Pt. For the latter atoms the
quasirelativistic effective core potentials of the
While the color band of the Pd complex is predicted to be red-shifted relative to the Ni complex, a blue shift is calcd. on passing from the Pd to the Pt complex. The blue shift is, in part, due to the relativistic contraction of bond lengths in the Pt complexes.
The origin of the color of 1,2-dithiins-interpretation by Kohn-Sham orbitals. Fabian, Jurgen; Mann, Matthias; Petiau, Maxime. Institut fur Organische Chemie, Technische Universitat Dresden, Dresden, Germany. Journal of Molecular Modeling (2000), 6(2), 177-185.
According to calcns. by time-dependent d.-functional theory (TD-DFT) the wine-red color of the half-chair (C2) 1,2-dithiin (1) is mainly due to a 1-electron transition between the frontier orbitals. These orbitals are characterized by local 2-center CC p bonds. The sym. HOMO of the twisted structure 1 correlates with the fully delocalized HOMO of the planar ref. structure with C2v symmetry. The anti-sym. LUMO correlates both with the essentially localized s* (SS) of the LUMO and the p* of the LUMO+1 of the planar compd. Thus the dominating 1-electron transition of 1 has some p®s* character in the terminol. of the planar system with a strong admixt. of the anti-bonding combination of the CC bond orbitals to the s*-type LUMO. The color of 1,2-dithiins are unique because of the simultaneous presence of a noncoplanar C=C bond system and the SS bond. For the sake of comparison calcns. were also performed at ab initio levels of theory (TD-RHF, SCI, EOM-CCSD and CASPT2). Although the absorption wavelengths are strongly underestimated by SCI and TD-RHF the order and the nature of the lowest-excited states are the same as those found by TD-DFT. The electron excitation of 1,2-dithiin is compared with that of 1,2-dithiane (3). The structure and the energetics of 1,2-dithiin are compared with 1,4-dithiin (4) and thiepin (5).
Properties, Oxidation, and Electrochemistry of 1,2-Dichalcogenins. Block,
Eric; Birringer, Marc; DeOrazio, Russell; Fabian, Juergen; Glass, Richard S.;
Guo, Chuangxing; He, Chunhong; Lorance, Edward; Qian, Quangsheng; Schroeder, T.
Benjamin; Shan, Zhixing; Thiruvazhi, Mohan; Wilson, George S.; Zhang,
Xing. Departments of Chemistry, State
Syntheses are presented of the 1,2-dichalcogenins: 1,2-dithiin, 1,2-diselenin, and 2-selenathiin, both substituted and unsubstituted. 1,2-Dithiin and 1,2-diselenin are prepd. by reaction of PhCH2XNa (X = S or Se) with 1,4-bis(trimethylsilyl)-1,3-butadiyne followed by reductive cleavage and oxidn. 2-Selenathiin is similarly prepd. using a mixt. of PhCH2SeNa and PhCH2SNa. Reaction of titanacyclopentadienes with (SCN)2 or (SeCN)2 followed by bis(thiocyanate) or bis(selenocyanate) cyclization affords substituted 1,2-dithiins or 1,2-diselenins, resp. With S2Cl2, 1,2-dithiins are directly formed from titanacyclopentadienes. Oxidn. of 1,2-dithiins and 1,2-diselenins gives the corresponding 1-oxide and, with 1,2-dithiins and excess oxidant, 1,1-dioxides; oxidn. of 2-selenathiin gives the 2-oxide. Electrochem. oxidn. of 1,2-dichalcogenins, which have a twisted geometry, affords planar radical cations by an EC mechanism. One-electron AlCl3 oxidn. of 3,6-diphenyl-1,2-dithiin gives the corresponding radical cation, characterized by EPR spectroscopy. Theor. calcns. result in a flattened structure for the 1,2-dithiin radical cation and a fully planar structure for the 1,2-diselenin radical cation. The 77Se NMR chem. shifts of 1,2-diselenin are characteristically high-field-shifted with respect to open chain diselenides in good agreement with results of GIAO-DFT calcns. based on MP2 and DFT optimum geometries.
Multiple minima hypersurfaces of water clusters for calculations of association energy. Montero, Luis A.; Molina, Jose; Fabian, Jurgen. Laboratorio de Quimica Computacional y Teorica, Facultad de Quimica, Universidad de La Habana, Havana, Cuba. International Journal of Quantum Chemistry (2000), 79(1), 8-16.
Multiple min. of water cluster hypersurfaces are explored to find thermodn. properties by means of the corresponding partition functions of their canonical distributions. The combination of semiempirical quantum chem. procedures for calcg. the cluster energies in local min. of supermols. and the statistical thermodn. approach for both the evaluation of macroscopic assocn. energies and the possible redn. by av. of abs. errors intrinsic to the parametrized Hamiltonian are shown to provide an appropriate model for comparison between exptl. and theor. results. The method can explicitly take into account environmental effects due to intermol. interaction. Water trimer and tetramer assocn. energies of -10.9 and -14.1 kJ/mol obtained from virial coeff. calcns. compare very well to the values of -10.5 and -16.4 kJ/mol, resp., found for the theor. assocn. energies in this paper.
1,3-Heterocumulene-to-Alkyne [3 + 2] Cycloaddition Reactions: A Theoretical and Experimental Study. Fabian, Juergen; Krebs, Adolf; Schoenemann, Dirk; Schaefer, Wolfgang. Institut fuer Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. Journal of Organic Chemistry (2000), 65(26), 8940-8947.
Transition structures and energy barriers of the concerted prototypical cycloaddn. reaction of 1,3-heterocumulenes (S:C:S, S:C:NR, RN:C:NR, and hetero analogs) to acetylene resulting in nucleophilic carbenes were calcd. by G2(MP2) and CBS-Q ab initio quantum chem. and by d. functional theory (DFT) methods. According to the calcns. the activation energies (activation enthalpies) of the homoheteroat. cumulenes decrease in the order O > S > Se and NH > PH and the reaction energies in the order O > S » Se and PH > NH. The reaction of CS2 and acetylene has a lower reaction barrier than that of carbodiimide and acetylene although the first reaction is less exothermic than the second one. The stronger cyclic stabilization of the 1,3-dithiol-2-ylidene in the transition state is discussed in terms of deformation and stabilization energies and of bond indexes. The known reactions of CS2 with ring-strained cycloheptynes were examd. by DFT and by DFT:PM3 two-layered hybrid ONIOM methods. In agreement with qual. exptl. findings the activation energy increases and the reaction energy decreases in the sequence S, SO2, and SiMe2 if CH2 in the 5-position of 3,3,7,7-tetramethyl-1-cycloheptyne is replaced by a heteroatom or heteroat. group, resp. The results of these calcns. were corroborated by exptl. studies with CSe2 and isothiocyanates as 1,3-heterocumulenes. The results of these calcns. were corroborated by exptl. studies with CSe2 and isothiocyanates as 1,3-heterocumulenes. Under more drastic conditions it was possible to add Me and Ph isothiocyanate, resp., to 3,3,6,6-tetramethyl-1-thia-4-cycloheptyne. The products are 1:3 (cycloalkyne:isothiocyanate) whose formation is explained by a trapping reaction of the first formed 1,3-thiazol-2-ylidenes.
Electronic excitation of sulfur-organic compounds - performance of time-dependent density functional theory. Fabian, Jurgen. Institut fur Organische Chemie, Technische Universitat Dresden, Dresden, Germany. Theoretical Chemistry Accounts (2001), 106(3), 199-217.
To define the scope and limitations of the time-dependent d. functional theory (TDDFT) method, spectral absorption data of a series of about 100 neutral or charged sulfur-org. compds. with up to 24 non-hydrogen atoms and up to four sulfur atoms were calcd. in the near-UV, visible and IR regions. Although the theor. vertical transition energies correspond only approx. to exptl. absorption band maxima, the mean abs. deviation was calcd. to be 0.21 eV (1600 cm-1). The main absorption features of various compds. with mono-coordinated or dicoordinated sulfur atoms are well reproduced. As far as possible TDDFT results were compared with those of semiempirical Zerner's INDO (ZINDO/S) and of PPP calcns. TDDFT also works well in cases where the semiempirical methods fail. Limitations of TDDFT were encountered with calcns. of spectral absorptions of dye mols. The "vinylene shift" of polymethine dyes is not reproduced by TDDFT. Whereas electronic excitation energies delocalized polar and betainic chromophores are reasonably well reproduced, excitation energies of charge-transfer-type and charge-resonance-type transitions of weakly interacting composite chromophores are significantly underestimated.
The thiocarbonyl chromophore. A time-dependent density-functional study. Petiau, M.; Fabian, J..Institut fur Organische Chemie, Technische Universitat Dresden, Dresden, Germany.THEOCHEM (2001), 538, 253-260.
D.-functional linear response theory calcns. allow a very satisfactory description of the spectral characteristics of thiocarbonyl compds. in the UV and visible region. The n p*- and p p*-type absorption bands are reasonably well reproduced by TD-DFT using the hybrid HF/DFT functional B3-LYP with the valence double-zeta basis set 6-31+G*. The abs. mean deviation is 0.20 eV for n p* and p p* transitions. The spectral shifts of the absorption bands with substitution are well reproduced. A third absorption band in the near-UV region is interpreted by TD-DFT and CASSCF/CASPT2 calcns. In the case of bis(trimethylsilyl) thioketone the theor. predictions were grossly at variance with the exptl. finding. According to the TD-DFT calcns. and to empirical considerations the exptl. result is wrong. The n p* absorption band is expected in the near-IR rather than in the visible region. This conclusion is supported by calcns. of spectral absorptions and 13C chem. shifts of related compds.
A combined density
functional and ab initio quantum chemical study of the Brandi reaction. Ochoa,
Estael; Mann, Matthias; Sperling, Dirk; Fabian, Jurgen. Laboratorio de Sintesis
Organica, Facultad de Quimica,
The Brandi reaction is the transformation of spiro[cyclopropane-1,5'-isoxazolidines] into tetrahydropyridones under thermal conditions. According to calcns. performed by the restricted and unrestricted d. functional theory and post-Hartree-Fock single- and multireference methods of ab initio quantum chem., the reaction proceeds through two biradical intermediates. These intermediates result from the homolytic cleavage of the N-O bond of the isoxazolidine ring in the first step, and the homolytic cleavage of one of the C-C bonds of the spiro-fused cyclopropane in the second. The activation energy of the rate-detg. first step of the parent reaction amts. to .apprx.40 kcal mol-1 at the RDFT/UDFT level of theory. This energy is not much higher than the energy of the first biradical intermediate relative to the reactants. The relative energies calcd. at the quadratic CI and coupled cluster ab initio level were of the same order of magnitude. The effects of structural modification of spiro[-cyclopropane-1,5'-isoxazolidines] by substitution at C or N in the five-membered ring, introduction of a double bond into the five-membered ring and replacement of the spiro-cyclopropane by spiro-cyclobutane are discussed. The theor. results reflect Brandi's exptl. findings on the reactivity of the compds. under conventional thermal or flash vacuum thermolysis conditions and his hypothesis about the reaction mechanism reasonably well.
Sulfur-containing mesoionic compounds: theoretical study on structure and properties. Fabian, Jurgen; Hess, B. Andes, Jr. Institut fur Organische Chemie der Technischen Universitat Dresden, Dresden, Germany. International Journal of Quantum Chemistry (2002), 90(3), 1055-1063.
The structure of the mesoionic 1,3-dithiolylium-4-olate (I) and thiopyrylium-3-olate (II) and of their derivs. were calcd. by first-principles methods. The compds. are considered as cyclic derivs. of open-chain thione S-ylides. The extent of cyclic electron delocalization was discussed in terms of the mol. charge distribution and nucleus-independent chem. shift values (NICs). The calcd. CS bond of S-C=O of I was found to be exceedingly long (>1.80 .ANG.). This result suggests a facile CS ring opening of I to S-ketenyl dithiomethyl ester. The transition structure of this reaction is nearly isoenergetic with the product of the reaction. The calcd. reaction barrier amts. to about 12 kcal/mol and the ring-to-chain valence isomerization should therefore occur under thermal conditions. This result is in line with the chem. reactivity of diphenyl-I. According to time-dependent d. functional theory calcns. (TD-DFT) the sulfur-contg. mesoionic compds. I and II should be colored. The intense long wavelength absorption of diphenyl-I at about 550 nm is well reproduced.
Calculation of excitation energies of organic chromophores: a critical evaluation. Fabian, J.; Diaz, L. A.; Seifert, G.; Niehaus, T. Institut fur Organische Chemie, Technische Universitat Dresden, Dresden, Germany. THEOCHEM (2002), 594(1-2), 41-53.
A series of org. compds. with first-row elements was calcd. to det. the performance of TD-DFRT (time-dependent d. functional response theory) and to compare with the performance of approx. or semiempirical methods (TD-DFRT-TB, ZINDO/S, PM3/S). The mean abs. deviation between theor. and exptl. excitation energies is lowest for TD-DFRT. Because of poor results in some cases the error of TD-DFT was distinctly larger in the calcns. of sulfur-free than in the calcn. of sulfur-contg. compds. General spectral absorption features are reasonably well reproduced by the approx. TD-DFRT in tight-binding approxn. (TD-DFRT-TB) and by semiempirical MO-CI methods based on the NDO (ZINDO/S) or the NDDO approach (PM3/S). If the limitations of ZINDO/S are considered the method is useful in calcg. n®p* and p®p*-type transitions.
Structural properties and 13C chemical shifts of bis- and tris(2-thienyl)methinium and related cations: a combined theoretical and experimental study. Fabian, Juergen; Hartmann, Horst; Noack, Antje. Technische Universität Dresden, Institut fur Organische Chemie, Dresden, Germany. Journal of Physical Organic Chemistry (2003), 16(1), 53-62.
The mol. structure of the parent bis- and tris(2-thienyl)methinium ions were studied by first-principles methods (second-order Moller-Plesset many-body perturbation theory and d. functional theory). In contrast to bis(2-thienyl)methinium, tris(2-thienyl)methinium is non-planar with torsion angles between the thienyl groups and the central plane of about 30°. The calcns. on tris(2-thienyl)methinium resulted in two almost isoenergetic conformers with barriers to isomerization less than 10 kcal mol-1 (1 kcal = 4.184 kJ). In order to discuss the 13C chem. shifts of Crystal Violet and of heteroanalogous compds. with thienyl-2-, with 5-amino-thienyl-2-, with 5-methylmercapto-thienyl-2- and with 5-amino-1,3-thiazolyl-2-heteroaryl groups, the structure was optimized at the DFT B3-LYP/6-31G(d) level and the chem. shifts were calcd. at the DFT-GIAO/6-311 + G(2d,p) level of theory. In general, the exptl. chem. shifts correlate very well with the exptl. values. The lowest energy electronic transitions in the UV-VIS region were calcd. by time-dependent d. functional response theory (TD-DFRT) using the DFT B3-LYP/6-31 + G(d) basis set. For cationic dyes the agreement between the results of TD-DFRT calcns. and expt. was less good than for neutral sulfur-contg. compds. Semiempirical calcns. (PPP, ZINDO/S) are better in that case and are more efficient.
absorption spectra of CCS- and CCS in neon matrices.
Riaplov, Evgueni; Wyss, Muriel; Maier, John P.; Panten, Dietmar; Chambaud,
Gilberte; Rosmus, Pavel; Fabian, Juergen. Department of Chemistry,
Mass selected C2S- ions have been co-deposited with neon to grow a matrix at 6 K. The A2.sum.+ ¬ X2.product. and B2.product. ¬ X2.product. electronic absorption spectra of the linear CCS- anion have been identified with origin band at 10 606 and 22 273 cm-1, resp. After exposure to UV radiation a new electronic transition (E3.sum.- ¬ X3.sum.-) of CCS is obsd. (origin band at 30 563 cm-1) in addn. to its known A3.product. ¬ X3.sum.- band system. Ab initio calcns. provide support for the symmetry assignment of the upper electronic states of CCS-, CCS and of the vibrational structure in the spectra.
of a Purported 1,2-Dioxin: A Combined Experimental and Theoretical Study. Block,
Eric; Shan, Zhixing; Glass, Richard S.; Fabian, Juergen. Departments of
3,6-Bis(p-tolyl)-1,2-dioxin (1g) was suggested by Shine and Zhao as a product in an electron-transfer (ET) photochem. reaction. This photoproduct is instead shown to be (E)-1,4-di-p-tolylbut-2-ene-1,4-dione ((E)-4a). Ab initio and DFT calcns. indicate that ring-closed 1,2-dioxin is thermodynamically far less stable than open-chain but-2-ene-1,3-dione. These calcns. indicate that (E)-4a is formed via the cation radical of 1g, which sequentially isomerizes to a novel s-radical with an O,O 3e bond [(Z)-4a]+.bul., undergoes ET to give (Z)-4a, and then photoisomerizes to (E)-4a.
Azabenzenes (azines) - the nitrogen derivatives of benzene with one to six N atoms: Stability, homodesmotic stabilization energy, electron distribution, and magnetic ring current; a computational study. Fabian, Juergen; Lewars, E. Institut fuer Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. Canadian Journal of Chemistry (2004), 82(1), 50-69.
The twelve azabenzenes - the species formed by replacing CH groups of benzene by N - were examd. computationally (with emphasis on the six contiguous-nitrogen species). MP2(fc)/6-31G*, B3LYP/6-31G*, CCSD(T)/6-31G*//MP2(fc)/6-31G*, and G3(MP2) calcns. were used to probe kinetic and thermodn. stabilities,
homodesmotic ring-opening energies, electron distribution (bond orders and lengths, Bird index), and NICS values, primarily to discern where the transition occurs from reasonably stable to highly fragile species. Some azabenzenes with three and those with four or more nitrogens are thermodynamically unstable, but kinetic stabilities indicated that, with the possible exception of hexaazabenzene, all the azabenzenes should be isolable, although some with four nitrogens might decomp. at room temp., and pentaazabenzene would require matrix isolation techniques. Although homodesmotic ring-opening reactions showed an almost monotonic decrease in the stability of the cyclic relative to the open-chain species (in appropriate ring-opening reactions) on going from benzene to hexaazabenzene, bond-order variation and NICS suggested this may be because of increasing destabilization by nitrogen lone pairs rather than because of a decrease in electron delocalization (in aromaticity).
1,3,2-Dioxaborines as potential components in advanced materials-a theoretical study on electron affinity. Fabian, Juergen; Hartmann, Horst. Institut fuer Organische Chemie, Technische Universität Dresden, Dresden, Germany. Journal of Physical Organic Chemistry (2004), 17(5), 359-369.
1,3,2-Dioxaborines with fluorine and other substituents at boron were calcd. by first-principles methods based on d. functional theory (DFT: B3-LYP) or many-body perturbation theory at the second order [MBPT(2): MP2]. 1,3,2-Dioxaborines are derivs. of 1,3-dicarbonyl compds. also known as 1,3-diketoborates. According to quantum chem. calcns., 2,2-difluoro-1,3,2-dioxaborines are of puckered structure with a low barrier to inversion. The calcd. charge distribution does not reflect well the traditional formula description. The boron atom carries a pos. rather than a neg. charge. Some compds. have a pronounced zwitterionic character accompanied by relatively high dipole moments. The calcd. pos. electron affinities (EAs) classify 1,3,2-dioxaborines as org. electron-acceptor compds. Depending on the type of substitution, the EAs vary between .apprx.0.5 and 3.5 eV (DFT calcns.). The EAs of various substituted 1,3,2-dioxaborines are of the same order of magnitude as those of quinones and close to electron affinities of strong org. acceptor compds. such as tetracyanoethylene (TCNE). Numerical predictions are verified by comparison with EAs of known medium-sized org. compds. studied exptl. and theor. at the same level of theory. In good agreement with results reported for other series of compds., the av. abs. error between theor. and exptl. EAs was 0.19 eV. Because of the ability of 3,5-diaryl-2,2-difluoro-1,3,2-dioxaboranes to fluoresce efficiently and to accept electrons easily, these compds. are potential candidates for future applications.
Chemical structure. Theory and experiment exemplified on 1,2-dichalcogenins. Fabian, Juergen; Mehlhorn, Achim. Germany. Wissenschaftliche Zeitschrift der Technischen Universitaet Dresden (2004), 53(3-4), 51-56.
Abstract A review. The term "chem. structure" was coined more than 100 years ago. Mols. were at that time considered to be composed of atoms connected by chem. bonds. The bonding pattern was depicted by structural formulas. Nowadays, the term structure covers more than just mol. topol. Three-dimensional mol. structures are now studied exptl. and theor. To illustrate the variety of structures, results are reported for a series of simple 6-membered ring compds., the so-called 1,2-dichalcogenins (C4H4X2, with X = O, S, Se, Te). The parent compds. were found to be puckered ring structures for S, Se, and Te. The structures contg. O are more stable as open-chain mols. The calcns. were performed using quantum chem. methods at the ab initio level of theory (MP2/6-311+G(2df,p)).
A combined experimental and quantum chemical study on the putative protonophoric activity of thiocyanate. Schönfeld, Peter; Montero, Luis; Fabian, Jürgen. Institut für Biochemie, Otto-von-Guericke-Universität Magdeburg, Magdeburg, Germany. Biophysical Journal (2005), 89(3), 1504-1515.
Inhibition of gastric acid secretion by thiocyanate is explained by a protonophoric mechanism assuming that thiocyanate induces a H+ back flux from the acidic gastric lumen into the parietal cells of gastric mucosa. Protonophoric activity of thiocyanate was examd. by swelling measurements using rat liver mitochondria and theor. by quantum chem. methods. Mitochondria suspended in K-thiocyanate medium plus nigericin (an H/K-exchanger) swelled when the medium pH was acidic, indicating that SCN- initiates a transfer of H+ across the inner membrane. To rationalize the protonophoric activity of thiocyanate, we considered the dehydration of SCN- to be crit. for transmembranal H+ transfer. For modeling this process, various hydrate clusters of SCN- and Cl- were generated and optimized by d. functional theory (DFT) at the B3-LYP/6-311++G(d,p) level. The cluster hydration energy was lower for SCN- than for Cl-. The total Gibbs free energies of hydration of the ions were estd. by a hybrid supermol.-continuum approach based on DFT. The calcd. hydration energies also led to the conclusion that SCN- is less efficiently solvated than Cl-. Due to the easier removal of the hydration shell of SCN- relative to Cl-, SCN- is favored in going across the membrane, giving rise to the protonophoric activity.
Radical Ions of a,a´-Bis(diphenylamino)-capped oligothiophenes: a combined spectroelectrochemical and theoretical study. Rohde, Dirk; Dunsch, Lothar; Tabet, Ahacine; Hartmann, Horst; Fabian, Jürgen,Leibniz-Institut für Festkörper- und Werkstoffforschung, Abteilung Elektrochemie und Leitfähige Polymere, Dresden, Germany. Journal of Physical Chemistry B (2006), 110(16), 8223-8231.
A new homologous series of a,a´-bis(diphenylamino)-capped oligothiophenes, prepd. by a Pd-catalyzed coupling reaction of stannylated 2-diphenylaminothiophenes with 2-mono- or 2,5-dibromothiophenes and their homologs, was studied by in situ ESR/UV-visible/NIR spectroelectrochem. In general, the oxidn. potentials of these oligothiophenes are proportional to the inverse no. of thiophene units. However, the potential slope of the 1st oxidn. is completely different from that of higher oxidn. steps. Trication radicals were identified by ESR for higher thiophene homologs in addn. to monocation radicals (polarons). According to the ESR hyperfine structures, the unpaired electron is delocalized in the conjugated system. In contrast to the parent a,a´-bis(diphenylamino)-capped oligothiophenes, the UV-visible/NIR absorption maxima of the oxidized species strongly depend on the no. of thiophene units. Spin-restricted and spin-unrestricted Kohn-Sham d. functional calcns. were used to explain and to understand these properties. Absorption wavelength and intensities were calcd. by the time-dependent d. functional response theory. Unrestricted d. functional calcns. of oligothiophene dications (bipolarons) with 5 thiophene rings result in spin-broken structures which may be considered as 2-polaron biradicals (polaron pairs).
Symmetry -lowering distortion of near-infrared polymethine dyes-a study by first-principles methods. Fabian, J. Institut für Organische Chemie, Technische Universität Dresden, Dresden, Germany. THEOCHEM (2006), 766(1), 49-60.
The shape of the longest-wavelength absorption band of near-IR (NIR) polymethine dyes in polar solvents is not well-understood. Among different tentative explanations a lowering of the mol. symmetry has been previously discussed. Polymethines of the symmetry point group C2v may undergo Peierl's distortion resulting in a structure of lower symmetry. A symmetry collapse was reported based on semiempirical AM1 calcns. The potential change of the mol. symmetry of polymethines was reexamd. by first-principle methods. As in the case of AM1 calcns. spin-restricted ab initio Hartree-Fock (RHF) calcns. of long-chain strepto[N]methines (1) and pyrido[N]methines (2) resulted in symmetry-lowered ground state structures. This occurs with N=19 for 1 and of N=11 with 2 at the RHF/6-31G* level. However, if electron correlation is taken into account by Moller-Plesset perturbution theory of second-order (MP2) or by d. functional theory (DFT) the classical sym. structures are favored. In contrast to spin-restricted DFT calcns. with Becke's three-parameter exchange functional (B3LYP), symmetry-breaking occurs at the DFT BHLYP level but at much longer-chain lengths than in the HF approxn. According to polarized continuum model (PCM) calcns., low-symmetry structures are favored in polar solvents. The interpretation of the absorption spectra of the polymethine dyes dissolved in polar solvents is more difficult as earlier assumed and addnl. exptl. studies are necessary to rationalize the nature of the NIR absorptions.
The absorption wavelengths of sulfur chromophors of ultramarines calculated by time-dependent density functional theory. Fabian, J.; Komiha, N.; Linguerri, R.; Rosmus, P. Institut für Organische Chemie, Technische Universität Dresden, Dresden, Germany. Journal Molecular Structure (THEOCHEM) (2006), 801(1-3), 63-69.
The neutral tetrasulfur and the trisulfur and tetrasulfur anion radicals were studied by d. functional theory (DFT) employing the hybrid functionals B3LYP, PBE0 and PB95 and large basis sets. The spectral data were obtained by time-dependent d. functional theory (TD-DFT). The calcd. absorption wavelengths for the calcd. vertical electronic transitions in the visible region were compared with the wavelengths of the absorption maxima of ultramarines and of synthetic sulfur compds. measured in matrixes or in soln. The chromophore of ultramarine blue was considered as a test case and the chromophore of ultramarine red studied in several model calcns. The calcd. transition energies and intensities favor the cis tetrasulfur chromophore of red ultramarine. The excellent agreement between the theor. and exptl. absorption wavelengths of the color bands supports earlier assignments. The electronic structure of cis and trans tetrasulfur is discussed in terms of ylidic and biradical resonance structures by natural resonance theory. The singlet ground states display RKS/UKS instability. The broken-symmetry UKS structure is of lower energy than the RKS structure, which does, however, not influence the mol. and electronic structure significantly.
On the electronic states of S4+ and S 4- isomers. Sormova, H. Linguerri, R. Rosmus, P.a Fabian, J:. Komiha, N. Laboratoire de Chimie Théorique, Université de Marne la Vallée Collection of Czechoslovak Chemical Communications (2007), 72, 83-99.
For three energetically most stable structures of tetrasulfur, S 4, S4+ and S4- (cis-chain, rectangular, and trans-chain forms), equilibrium geometries, harmonic wavenumbers, ionization energies, electron affinities, electronic vertical and adiabatic excitation energies, and electronic transition moments were calculated by ab initio methods. It was found that similarly to the ground state of S4, the S4+ cix-isomer could interconvert, perturbed, however, by vibronic coupling with a very close-lying excited state and large-amplitude vibrations. Moreover, the cis- and rectangular minima are calculated to be energetically degenerated. The ω values in all three species agree reasonably well with existing experimental and theoretical data. The calculated patterns of harmonic modes suggest the existence of very complex low-lying anharmonic polyads in all three species. The calculated ionization energies reported previously are compared with the present more accurate data. Also the electronic transition moments and the energy positions of the electronic states with higher spin multiplicities are given.
Structure and properties of a-cyclo[N]thiophenes as potential electronic materials - A theoretical study. Fabian, Juergen; Hartmann, Horst. Institut fuer Organische Chemie, Technische Universitaet Dresden, Dresden, Germany. Journal of Physical Organic Chemistry (2007), 20(8), 554-567
D. functional theory (DFT) calcns. of ring-shaped a-cyclo[N]thiophenes with N = 2 to N = 18 have been performed for ideal structures of high symmetry (point groups Cnv and Dnh) and for optimum energy structures of lower symmetry (D2d, Cs, C2v, Ci or C1). Whereas the first three members of the series behave exceptionally the higher members are typical cyclothiophenes consisting of weakly interacting thiophene rings. In contrast to neutral compds., cations and dications of cyclothiophenes with N ³5 exhibit pronounced electron delocalizations along the carbon backbone. However, if the functional B3LYP is replaced by BH cations of large ring-size cations show polaron-type charge defects. According to broken symmetry DFT calcns. dications with N = 14 and N = 18 have biradical character. These structures correspond to two-polaron-type structures rather than to dipolarons. The calcd. vertical ionization energies of cyclo[N]thiophene are comparable with those of oligo[N]thiophenes of the same no. of thiophene rings but the calcd. abs. energies are probably too low at large ring size. Cyclothiophenes absorb light of lower energies than the related oligothiophenes. Cyclothiophenes belong to the strongly absorbing org. chromophores. In case of high mol. symmetry some of the excited states of cyclothiophenes are degenerate. The degeneracy is lifted with lower symmetries but the general absorption feature remains. The theor. results are discussed with respect to recent exptl. findings.
Electronic states of the ultramarine chromophore S3-
The potential energy surfaces and the spin-orbit couplings for states correlating with the lowest dissociation asymptote S2(X 3∑g-) + S-(2P) of the radical anion of thiozone have been calculated by full valence complete active space self-consistent field (CASSCF), internally contracted multi-reference configuration interaction (IC-MRCI) and for some of the states also by restricted coupled cluster with perturbative triples (RCCSD(T)) ab initio methods. For six electronic states lying below the electron detachment threshold: X2B1, A2B2, B 2A1, C2A2, 4∑ g-, and the second 2A1, equilibrium geometries and harmonic wavenumbers are reported. For the ground state also anharmonic vibrational levels have been evaluated. Due to the intensity borrowing via vibronic coupling with the B2A1 state also the dipole forbidden A-X transition becomes allowed in the Franck-Condon region of the UV spectrum. The C2A2 state responsible for the blue color of ultramarine correlates adiabatically with the first dissociation asymptote S2(X3∑g-) + S -(2P). Along the dissociation path the regions of vibronic and spin-orbit couplings were located. For the Rs2-s larger than about 2.6 Å the electron spin-states of the lowest dissociation asymptote are strongly mixed. The properties of the S3- electronic states are compared with those of O3-.
Chromophores of neutral and dicationic thiophene-based oligomers - A study by first-principle methods. Fabian, Juergen; Hartmann, Horst. Fachbereich Chemie, Technische Universitaet Dresden, Dresden, Germany. Dyes and Pigments (2008), 79(2), 126-139.
Time-dependent d. functional theory (TD-DFT) and semiempirical methods (ZINDO-CIS, PPP-CIS) were applied to colored neutral and dicationic thiophene-based oligomers; in addn. to the parent oligothiophenes and various a,a'-end-capped derivs., oligothiophenes with thiophene rings linked by methine, vinylene or phenylene groups were studied. Being p-chromophores, the compds. absorbed intensely in the Vis-NIR region; variation of the absorption energy with the reciprocal of the no. of thiophene rings resulted in low band gap (as is known for low band gap polymers). While the parent oligothiophenes displayed no singlet/singlet instability up to the octadecithiophene, the long chain oligomers were singlet/triple unstable. According to BS-UDFT calcns., biradical oligomers (two-plarons) were slightly favored over conventional dications (bipolarons). The color-detg. electronic transitions of large size oligothiophenes calcd. by open shell TD-DFT were little shifted in energy relative to those calcd. using closed shell TD-DFT. The electronic structure of the oligomers is discussed in terms of bond length alternation and nucleus-independent chem. shifts.
TDDFT-calculations of Vis/NIR absorbing compounds. Fabian, Juergen. Technische Universitaet Dresden, Fachbereich Chemie und Lebensmittelchemie, Dresden, Germany. Dyes and Pigments (2010), 84(1), 36-53.
To examine the strengths and limitations of the time-dependent d. functional theory in calcg. the absorption wavelengths of dye, 130, non-radical, radical and biradical colored org. compds., including perylenimide, porphyrin, azobenzene, quinone, croconaine, squaraine and push-pull-type colorants, were randomly selected. The first intense electronic transitions were satisfactorily calcd. using time-dependent d. functional theory. While polymethine dyes behaved exceptionally, the calcd. transition energies for cyanines, oxonols and various related dyes were systematically too large. Broken-symmetry unrestricted d. functional calcns. revealed the biradical character of several quinoid compds. derived from p-quinodimethane as well as that of some non-Kekule-type structures.
On the nature of some biradicaloid and antiaromatic Vis/NIR-chromophores. Fabian, Juergen; Peichert, Rasmus. Fachbereich Chemie und Lebensmittelchemie, Technische Universitaet Dresden, Dresden, Germany. Journal of Physical Organic Chemistry (2010), 23(12), 1137-1145.
Dyes derived from the
biradicalic oxyallyl and cyclopentadienylium were calcd. by time-dependent d.
functional theory (TDDFT) and the characteristics of the prominent low-energy
transitions revealed by graphical means.
According to theor. and exptl. studies, 4-aminophenyl-substituted dyes
absorb intensely at long wavelengths up to the near IR. If the amino groups are removed the
absorption wavelengths are changed little.
As found in the previous studies on the squaraine and croconaine
oxyallyl dyes, the substituents play only a minor role in the spectral
excitations do not occur between the donor aryl substituents and the central
oxyallyl or cyclopentadienylium acceptor group.
This behavior is exceptional since donor-acceptor compds. tend to
produce charge-transfer- or polymethine-type electronic transitions. The hitherto rarely used electron d.
difference (EDD) maps clearly unveiled the spectral excitation features. The spectral excitation of the title compds.
is predominantly localized at the oxyallyl and cyclopentadienylium groups,
resp. Characteristics of simple
chromophoric compds. and of conventional