Ab initio SCF and CI study of the electronic spectrum of pyridine N-oxide

Configuration interaction (CI) studies of ground, n *, * * electronically excited states are reported for pyridine N-oxide. The transition energy to the lowest * excited ¹ B ₂ state is calculated at 4.35 eV, compared to the experimental spectrum range of 3.67–4.0 eV. This state lies below the lowest n * excited ¹ A ₂ state calculated at 4.81 eV above the ground state. The only experimentally reported triplet state at 2.92 eV above the ground state is predicted to be the ³ A ₁ (*) state. The calculated energy lies at 3.27 eV. Numerous other high-lying singlet states as well as the triplet states have also been calculated. The intramolecular charge transfer character of the ground and the excited states have been studied in terms of the calculated dipole moment and other physical properties.     

Charge control in the formation of complexes of phenol with unsaturated compounds containing organometallic substituents from group IV

The resonance donor effect of the , conjugation of R₃M and R₃MCH₂ (M = Si, Ge, Sn; R is an alklyl group) substituents with the triple bond in compounds R₃MC=CX and R₃MCH₂CCX (X = H, R) changes on passing from isolated molecules to their H-complexes. A partial ⁺ charge on the triple bond enhances , conjugation; a partial ^– charge on the triple bond has practically no effect on the resonance properties of R₃M substituents, whereas the , conjugation of R₃MCH₂ substituents diminishes owing to the effect of negative direct resonance interaction. The effect of , conjugation on the effective negative charges of the carbon atoms in the -CC- fragments was estimated quantitatively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1041–1046, June, 1994.This work was supported by the Russian Fundation for Basic Research (Grant 93-03-18372).     

Homodimerization of spiro{bicyclo[2.2.1]Hepta-2,5-Diene-7,1′-cyclopropane}, catalyzed by group VIII transition metal complexes

Conclusions The homodimerization of spiro{bicyclo[2.2.1]hepta-2,5-diene-7,1-cyclopropane} (I) has been investigated in the presence of Ni-, Fe-, Co-, Rh-, and Ir-based metal complex catalysts. Depending on the nature of the metal and its ligand environment cyclodimerization of (I) can take place via [2+2]-, [2+2+2]-, and [4+4]-cycloaddition schemes, to give high yields of hepta-, octa-, and nonacyclic strained hydrocarbons.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2592–2599, November, 1988.     

Study of the effects of conjugation in alkenyl derivatives of silicon and germanium by infrared spectroscopy

Conclusions The effects of d-p and, conjugation in the vinyl and allyl derivatives of silicon and germanium depend on the nature of the other three substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2074–2076, September, 1971.     

Vacuum ultraviolet absorption spectra of vinyl compounds containing elements of group IV

Conclusions The substituants MR₃ in the compounds C=C-MR₃ and R₃M-C=C-MR₃ give rise to a bathochromic effect in the UV absorption spectra. The influence of the substituents does not agree with a mechanism of d- conjugation, and its explanation requires a consideration primarily of the - conjugation, and to a lesser degree of the inductive effect.     

Spectroscopic manifestation of the accidental degeneracy of π=Δ electronic adiabatic terms of linear triatomic systems

The semiclassical form of the absorption band of a linear triatomic system which corresponds to an electronic transition from the -ground state term to the excited intersection and terms was calculated. The analysis was carried for negligibly small defect of frequencies and in the absence of a shift of the equilibrium position on excitation. The experimentally observed CuCl₂ absorption spectrum was interpreted qualitatively as a , gS transition on the existence of a point of = accidental degeneracy. The 7000–24000 cm^–1 energy interval in the spectrum was analyzed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 222–225, March–April, 1988.     

Tautomerism,electronic structures,and electronic spectra of indolo[2,3-b]quinoxaline and its derivatives

The tautomerism, electronic spectra, and electronic structures of the ground and excited states of indolo [2,3-b]quinoxaline and its 2,3- and 1,4-dibutoxy derivatives were investigated by the Pariser-Parr-Pople (PPP) method. It is shown that these compounds exist primarily in the 6H form; the long-wave s^* transition is due to transfer of charge from the indole fragment to the quinoxaline fragment, and in the first excited state many of the bonds in the quinoxaline fragment are loosened significantly. The effect of butoxy substituents on the first s^* transition of indolo [2,3-b] quinoxaline was analyzed by means of perturbation theory within the framework of the Hückel MO method.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1259–1263, September, 1982.     

Electronic structure and aromaticity of planar singlet π-electron monocyclic π2 carbenes

Induced -electron ring currents and relative diamagnetic susceptibilities of planar singlet -electron monocyclic ² carbenes are calculated in the coupled variant of perturbation theory in the CNO method. It is shown that the parity theorem holds for charged planar ² and ² carbenes formally generated by the detachment of a proton or a hydride ion from alternant hydrocarbons. This leads, in such carbenes, to the same energies of singlet-singlet and singlet-triplet transitions, electric polarizabilities, conjugation energies, -electron ring currents, diamagnetic susceptibilities and current contributions to chemical shifts, whereas the charge contributions to the latter are of opposite signs.Donbas State Academy of Building and Architecture, 1 Derzhavina St., 339023 Makeevka, Donetsk Region, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 157–162, May–June, 1996. Original article submitted December 5, 1994.     

MO-Berechnungen an Heterocyclen, 4. Mitt.1: Zum Einfluß der Ladungsterme in den Diagonalelementen derHamilton-Matrix von self-consistent-Verfahren auf die Berechnung von π-Elektronendichten und Bindungslängen

Zusammenfassung Mit SC- und SC_, -MO-Methoden werden die grundlegenden Einflüsse von Ladungstermen in derHamilton-Diagonalmatrix auf -Elektronendichten und Bindungslängen weiter studiert, insbesondere an N-Heterocyclen (Benzologe des Pyrrols und Pyridins). Im Vergleich mit erweiterten -Elektronenansätzen vom SCF—PPP-Typ liefern die einfachen, auf einige wesentliche Terme reduzierten SC-Matrixelemente sehr gute Resultate.

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The influence of charge terms in the hamilton diagonal-Matrix of self-consistent methods on the calculation of -electron densities and bond lengths

SC- and SC_, -MO methods are applied to the study. Subjects of the calculations are N-heterocycles (pyrrole and pyridine series). Simple SC matrix elements, which were found to include the essential terms, give good results in -electron densities and bond lengths.

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3. Mitt.:M. Scholz undD. Heidrich, Mh. Chem.99, 588 (1968).     

13C and 29Si NMR spectra and intramolecular interactions in derivatives of phosphaalkenes R-P=C[Si(CH3)3]2

Analysis of the ¹³C, ²⁹Si, and ³¹P NMR spectra in the series of C-bis(trimethylsilyl)phosphaalkenes made it possible to differentiate between the mechanisms of the electronic effects of the substituents R at the P atom on the -system of the -P=C(SiMe₃)₂ group. It was established that substituents R capable of n (or ) conjugation (NMe₂, OR, Hlg) substantially perturb the -system, destabilizing the levels of the occupied MO of the P=C bond; substituents with poorly defined -donating (accepting) characteristics (tert-Bu, iso-Pr, CN, Ph) only influence the investigated system through its polarization. Criteria which agree with the reactivity characteristics of the phosphaalkenes were obtained.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 729–733, November–December, 1988.     

Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

Spectroscopic study of organosilicon derivatives of thiophene

Substituents in disubstituted thiophenes have an additive effect on the chemical shifts of the ring hydrogen atoms. The electronic effects of organosilicon substituents are transmitted via inductive and conjugation (d-p interaction) mechanisms. The effect of d-p interaction in the Si-ring bond is absent for Si(OC₂H₅) and SiF₃ substituents.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenli, No. 11, pp. 1483–1488, November, 1972.     

Crystal,molecular, and π-electronic structure of 1,3,2-benzodithiazolium chloride

X-Ray diffraction examination and MNDO calculations have shown that 1,3,2-benzodithiazolium chloride (I) is ionic, with a planar heteroaromatic 10-electron cation. The -MO of the cation (I) is isolobal with the p-MO of benzo-2,1,3-thiadiazole. In the cation of (I), as in the latter compound, the p-AO of nitrogen and sulfur contribute for the most part to -MO of differing symmetry (b₁ and a₂, respectively). This has the consequence that although both nitrogen and sulfur participate in the formation of a single -system in the thiazolium cation of (I), there is virtually no -bonding between them. Generally speaking, the -MO of the (I) cation shows a tendency to localization on separate molecular fragments. The charge on the cation is localized at the SNS group, and the five-membered ring is strongly polarized. These features all reduce the heteroaromaticity of the system.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1683–1688, December, 1990.     

Research on 1-aza two-ring systems

Reduction of 5-[2-(methoxycarbonyl)ethyl]-1,3-dihydropyrrolizines with lithium aluminum hydride gave 5-(-hydroxypropyl)-1,2-dihydropyrrolizines (in 70–90% yields), which have intramolecular -hydrogen bonds in dilute solutions. The parameters of the -hydrogen bonds were determined in the IR spectra, and their enthalpies were found. The data obtained (_OH 95–99 cm^–1, –H 3.05 kJ·mole^–1) show that among compounds with an aliphatic hydroxyl group and a system of electrons, 5-(-hydroxypropyl)-1,2-dihydropyrrolizines have some of the strongest intramolecular -hydrogen bonds.See [1] for communication XVI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 359–363, March, 1978.     

Copper(II)-disulphide interaction: a spectroscopic and electrochemical study of the interaction of copper(II) with an imidazole-containing disulphide

Summary The interaction of copper(II) salts with the imidazole-containing disulphide 5-(1,2,5-dithiazaepan-5-ylmethylene)-4-methyl-2-ethyl imidazole (MAMI) in MeOH have been investigated. The 11 Cu(ClO₄)₂MAMI system exhibited a single ligand field band at ca. 12200cm^-1, an intense shoulder at ca. 31500 cm^-1 and a less intense split feature at 24400 and 25300cm^-1 assignable to S() Cu^II and S() Cu^II charge transfer (CT) transitions, respectively. The e.p.r. parameters suggested the presence of a CuN₂SO chromophore, however; the 11 Cu(NO₃)₂MAMI system did not exhibit a S Cu^II CT band and the g value was comparatively high. An electrochemical study of the 11 Cu(ClO₄)₂MAMI system in MeOH revealed that the copper-disulphide interaction, though weaker, would confer a high redox potential as well as reversibility, similar to the copper-thioether interaction.     

MO LCAO calculations and the electronic spectra of the anions of cyclopent-4-ene-1,3-diones and indane-1,3-diones

The Hückel approximation in MO LCAO is used to show that the anion system of cyclopent-4-ene-1,3-dione should have two ^* transitions: a weak one at long wavelengths, NV₁, and a strong one at short wavelengths, C=C(1,3)V₁. An ethylene, phenyl, or acyl group at position 2 gives rise to a new strong band, NC=C(2), Nbenz, or NC=O (2). A p-nitrophenyl group at position 2 gives rise to a strong NNO₂ band, which overlaps the weak NV₁ band, while the Nbenz band becomes weak and is virtually lost from the spectrum.     

Unambiguous Determination of the Absolute Configurations of Acetylene Alcohols by Combination of the <Emphasis Type="Italic">Sonogashira</Emphasis> Reaction and the CD Exciton Chirality Method – Exciton Coupling between Phenylacetylene and Benzoate Chromophores

Summary. The CD exciton chirality method was applied to various phenylacetylene alcohols to determine their absolute configurations; the long axis polarized –^* transition (_max=252nm) of the 4-methoxyphenylacetylene chromophore couples with the transition (_max=257nm) of the 4-methoxybenzoate group to generate intense exciton split CD Cotton effects, from the signs of which the absolute configurations of phenylacetylene alcohols were unambiguously determined. As an extension of the results, a new methodology for determining the absolute configurations of acetylene alcohols having the HCCCH(OH)-moiety by combination of the Sonogashira reaction and the CD exciton chirality method has been developed and applied. Since the –^* transition of acetylene triple bond is located below 180nm, it is difficult to observe ideal bisignate CD Cotton effects due to the exciton coupling between acetylene and benzoate chromophores. To observe the ideal exciton split Cotton effects necessary for the unambiguous determination of absolute configuration, the terminal acetylene group was converted, by the Sonogashira reaction, to the 4-methoxyphenylacetylene moiety, which exhibits an intense –^* absorption band polarized along the long axis of the chromophore at 252nm. As a partner of exciton coupling, 4-methoxybenzoate showing a –^* band at 257nm was introduced into the alcohol moiety, and the benzoates formed showed intense bisignate CD Cotton effects, from the signs of which the absolute configurations of original acetylene alcohols could be determined in an unambiguous manner.     

New form of effective potential to calculate polarization effects of theπ-electronic states of organic molecules

A new relation for the contribution of the most important polarization effects in the energy of the -electronic states of organic molecules is derived. For -electronic systems we suggest a correct form of the ejfective potential of the two-panicle polarization interaction of -electrons via the polarizable -core. This form approximates (by the Thomas-Fernti method) the exact contribution of the corresponding exchange polarization diagrams of the Rayleigh-Schrödinger perturbation theory. The potential may be flectively used in ab initio calculations of -electronic systems typically done in the frozen core approximation.Hydrometeorological Institute, Ukraine. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 12–19, September–October, 1993.Translated by L. Smolina     

Nature of the pentamethyldisilanyl group in organosilicon compounds

Summary The positige inductive effect of the pentamethyldisilanyl group (CH₃)₃SiSi(CH₃)₂ and the election-acceptor effect of its p-d bond with an aromatic ring are appreciably greater than the analogous effects of the trimethylsilyl group (CH_{3 3}Si, which gives ground for the postulation of the presence of a p-d-d¹ bond in the fragment C_sp ²-Si-Si.     

A 2pπ, 3dπ valence bond wave function for the 1B1u state of ethylene

A 2p, 3d valence bond wave function for the lowest ¹ B _1u state of the -system of ethylene is variationally optimized with respect to the atomic orbital exponents using a non-empirical -approximation. The resulting energy compares favourably with previous calculations and leads to a satisfactory value for the lowest ¹ A _1g-¹ B _1u transition energy. The optimized exponent for the 2p orbital is close to the Slater value whereas the exponent for the 3d orbital is found to be nearly hydrogenic. The implications of this result are discussed in some detail.

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Zusammenfassung Für den tiefsten ¹ B _1u -Zustand des -Elektronensystems des Äthylens wird nach der Variations-methode eine 2p, 3d-Valenzbindungs-Wellenfunktion bezüglich der Orbitalkoeffizienten optimiert, wobei eine nicht-empirische -Approximation zugrunde gelegt wird. Die berechnete Energie stimmt gut mit den Ergebnissen vorausgegangener Rechnungen überein. Für den tiefsten ¹ A _1g ¹ B _1u -Übergang ergibt sich ein befriedigender Energiewert. Der optimierte Orbitalkoeffizient für das 2p-Orbital stimmt gut mit dem nach der Slaterschen Regel bestimmten Koeffizient überein, während man für den 3d-Orbitalkoeffizienten einen Wert findet, der dem des Wasserstoffs ähnlich ist.

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Résumé Une founction d'onde V.B.(2p , 3d ) est optimée pour l'état ¹ B _1u d'aethylen. L'energie calculé aussi que l'energie de transition la plus basse ¹ A _1g -¹ B _1u est en bon accord avec des valeurs connues.