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G. G. Dyadyusha I. V. Repyakh A. D. Kachkovskii 《Theoretical and Experimental Chemistry》1985,21(2):131-139
The behavior of the bond orders in symmetric model polymethine dyes has been investigated by the HMO, PPP, and CNDO/2 methods. It has been established that the greatest equalization of the bonds is achieved in the case of dyes with moderately basic terminal groups. In other cases, alternation of the bond orders, which diminishes with increasing length of the polymethine chain and attenuates with increasing distance from the end, has been discovered at the ends of the polymethine chain. The amplitude of the alternation of the bond orders in a polymethine chain is greater, the more the basicity of the terminal groups, as characterized by the electron-donor parameter o (0 o 90°), deviates in either direction from the mean (o = 45°). It is considerably smaller in the first excited state than in the ground state. The -electronic approximation is a correct method for describing the electronic structure of a polymethine chain. The neglect of the electrons can distort the bond orders of the terminal groups.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 138–146, March–April, 1985. 相似文献
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Yu. V. Babin V. M. Mamaev Yu. A. Ustynyuk V. V. Gorchakov 《Theoretical and Experimental Chemistry》1990,25(4):450-454
The tautomerization energies for the reaction R2P(O)H R2P-OH, where R= OH, OCH3, OC2H5, CH3, and CF3, have been calculated by the CNDO/2 method with optimization of the exponents of the Slater 3d AO's according to the criterion of a minimum total energy for the molecule. The results are in qualitative agreement with the experimental data. The MNDO and CNDO/2 calculations with the use of a standard sp basis predict greater stability for the structures with a three-coordinate phosphorus atom, in contradiction to experiment.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 486–490, July–August, 1989.In conclusion, we express our thanks to V. L. Foss for showing an interest in this work and for some valuable discussions. 相似文献
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G. I. Kagan V. A. Kosobutskii V. K. Belyakov O. G. Tarakanov 《Chemistry of Heterocyclic Compounds》1973,9(10):1265-1270
Those structures of aromatic imidazoles that can be realized in polybenzimidazoles were investigated within the framework of the computational scheme of the Pariser-Parr-Pople method. The features of the electronic structures of the investigated molecules were exposed. A judgment is expressed relative to the strength characteristics of the bonds in the imidazole rings during thermal or thermal oxidative destruction of aromatic polybenzimidazoles. The stereoisomerism of dibenzimidazoles was examined. The UV absorption spectra of the investigated compounds were interpreted.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 10, pp. 1396–1402, October, 1973. 相似文献
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G. I. Kagan V. A. Kosobutskii V. K. Belyakov O. G. Tarakanov 《Chemistry of Heterocyclic Compounds》1972,8(6):717-721
Indigo and its dimer, trimer, dehydro, and leuco forms were investigated within the framework of the Pariser-Parr-Pople method. The electronic structures of the compounds in the ground and excited states and the effect of chain lengthening are discussed, and the UV absorption spectra are interpreted. Several characteristics of the chromaticity of the investigated compounds as representatives of vat dyes are examined. The estimated (from calculations) energetic favorability of the indigoid, dehydro, and leuco forms of indigo is used in discussing the observed and experimental ease of redox transformations of indigo.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 794–798, June, 1972. 相似文献
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G. I. Kagan V. A. Kosobutskii V. K. Belyakov O. G. Tarakanov 《Chemistry of Heterocyclic Compounds》1974,10(2):166-170
The characteristics of the electronic structures of a number of model aromatic oxazoles realized in aromatic polyoxazoles were obtained within the framework of the Pariser-Parr-Pople method. The UV spectra of most of them were interpreted. The stereoisomerism of dibenzoxazoles is examined. 相似文献
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G. I. Kagan V. A. Kosobutskii V. K. Belyakov O. G. Tarakanov 《Chemistry of Heterocyclic Compounds》1972,8(8):949-955
The results of calculations by the Pariser-Parr-Pople method and the expanded Hückel method of oligomeric compounds and fragments from which aromatic polyimide macromolecules are constructed are presented and discussed. In connection with the controversial character of the problem of the structures of the intermediates in the destruction of polyimides and the use, in this case, of the concept of imide-isoimide rearrangement, the relative advantageousness of the tautomeric forms of imides is evaluated, the participation of the imide ring in one or another form in conjugation is discussed, the spectral differences in the forms are established, etc. The strength characteristics of the bonds in polyimides were estimated in connection with the possibility of homolytic and hydrolytic cleavage of polyimides at these bonds.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.8, pp. 1048–1056, August, 1972. 相似文献
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V. K. Yatsimirskii L. P. Oleksenko A. V. Arkharov 《Theoretical and Experimental Chemistry》1992,28(1):38-43
The MNDO method has been used in a quantum-chemical calculation of the electronic structure of complexes IFR...H2O and IFR...2H2O (IFR is an ice-forming reagent — 1,3,5-trihydroxybenzene, 1,5-dihyrdoxynapthalene, or 2,6-dihydroxynaphthalene), with complete optimization of geometry. The calculated results are compared with data on the ice-forming activity and structural features of the crystals of these IFRs.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 41–47, January–February, 1992. 相似文献
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V. V. Varfolomeeva 《Russian Journal of General Chemistry》2011,81(9):1812-1817
New results of the study of stable intermediates containing an intramolecular hydrogen bond O-H…O=C in the gas phase and solvents,
carbon tetrachloride and dioxane, were analyzed. The structural and energy characteristics of the stable conformers of these
compounds were determined by a MR2/6-311++G(d, p) method. The most stable is the hydrogen-bonded conformer of 1-hydroxy-1-chloroethyl
acetate molecule. The approaches to accounting for the effects of the O-H…O=C intramolecular hydrogen bonding on the molecules
reactivity were discussed. 相似文献
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G. N. Kartsev N. M. Klimenko Zh. E. Grabovslzap G. M. Chban 《Journal of Structural Chemistry》1990,31(1):146-149
M. V. Lomonosov Moscow Institute of Fine Chemical Technology. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 1, pp. 161–164, January–February, 1990. 相似文献
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Ab initio Gaussian type calculations are reported for the ground and excited states of the hypothetical molecule formaldimine (H2CNH). The C=N group is compared with the C=O group.
Zusammenfassung Die Ergebnisse einer ab initio Rechnung mit Gau\-Orbitalen für das hypothetische Formaldimin-Molekül (H2CNH) werden mitgeteilt. Es werden sowohl Grundzustand als auch einige angeregte ZustÄnde untersucht und die beiden Gruppen C=O und N=O verglichen.
Résumé On présente les résultats de calculs ab initio utilisant une base Gaussienne pour la molécule hypothétique de formaldimine (H2CNH). L'étude porte sur l'état fondamental et quelques états excités. Une comparaison est faite entre le groupement C=N et le groupement C=O.相似文献
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G. N. Kartsev N. M. Klimenko Zh. E. Grabovskaya G. M. Chaban 《Journal of Structural Chemistry》1989,29(6):931-933
M. V. Lomonosov Institute for Fine Chemical Technology, Moscow. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 6, pp. 126–128, November–December, 1988. 相似文献
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Equilibrium structural parameters, atomic charges, and quadrupole moments of the molecules of 2,4,6-tris(diazo)cyclohexane-1,3,5-trione,
3,6-bis(diazo)cyclohexane-1,2,4,5-tetraone and its anion, isomeric 3,6-bis(diazonium)cyclohexanediondioles and 4,4′-bis(diazonium)-1,1′-biphenyl
in a vacuum and in dichloromethane were calculated by the quantum chemical method PBE0/cc-pVTZ using the polarizable continuum
model (PCM).The p-quinoid dication is more favorable than o-quinoid dication by 20 kcal mol-1 in a vacuum and by 13 kcal mol−1 in dichloromethane.The norm of the quadrupole moment of the centrosymmetric molecules in a polarizable medium increases while
that of the dications decreases. The quadrupole polarization of molecules and molecular ions by the solvent does not change
their symmetry point group. 相似文献
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V. I. Minkin A. G. Starikov R. M. Minyaev A. A. Starikova 《Theoretical and Experimental Chemistry》2011,46(6):363-370
The complexation of chromenes with transition metal ions was studied using the B3LYP*/6-311++G(d,p) method. We are the first
to show that transformation of the spin state of a transition metal complex through an LD LISC mechanism can be achieved by
means of configurational isomerization of the metal-chelate coordination site induced by ligand rearrangement. 相似文献
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The coordination number of silicon in silicon-oxygen compounds: the special case of 6-fold coordination in thaumasite 总被引:1,自引:0,他引:1
In most silicon-oxygen compounds, the silicon atom is 4-fold coordinated. Exceptionally, silicon is found in 6-fold coordination, as in the mineral thaumasite, which also may be formed in the degradation, and sometimes subsequent weakening, of certain concretes. The connection between coordination number and chemical bonding in oxidic compounds generally is explored using the optical basicity concept to estimate the extent of negative charge provided by oxide(-II) donor atoms in the coordination sphere. A correlation is established between this charge and the heat of formation of silicate (per oxide(-II) atom), which indicates that reduction in charge decreases thermodynamic stability. Calculations for thaumasite show that 4-fold coordination would provide a very small charge, but that 6-fold provides a charge comparable with that for stable 4-fold coordinated silicates such as K2Si2O5. 相似文献
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S. N. Slabzhennikov A. V. Kashin L. N. Alekseiko 《Theoretical and Experimental Chemistry》1992,28(1):35-37
Results are presented from modeling the complex H3PO...HF by the ab initio Hartree-Fock-Roothaan method. A generalized method is proposed for the quantitative fragmentary analysis of molecular orbitals (MOs). It is shown that when the complex is formed, the chemical bond between the phosphine oxide and the HF molecule is formed by means of a shift of the electron pair of the -bond of the HF to a 2p orbital of the O atom and the formation of a bonding three-center MO localized on the O, H, and F atoms, and also through a shift of an electron pair from the O atom to a 2p orbital of the F atom and the formation of a nonbonding MO localized on the O and F atoms.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 38–41, January–February, 1992. 相似文献