Quantum-chemical study of allylic compounds with two bonded heavy atoms

It has been shown by the CNDO method that the bathochromic shift of the long-wave absorption band in the transition from allylstannane to compounds of the type C=C-C-Sn-X and C=C-Sn-X (where X is a heavy atom) is connected with the formation of a low-energy vacant *_S-X orbital, localized mainly in the region of the Sn-X chemical bond, and of an occupied _Sn-X orbital, the energy of which is somewhat higher than of the _C-Sn orbital. The dependence of the position of the long-wave absorbance region on conformation is related to the fact that, in planar and nonplanar conformers, the long-wave transitions are of a different type ( * and *, respectively); the bathochromic shift is determined to a large degree by the difference in the energies of the highest occupied MO ( - ) in the s-trans form. In the nonplanar conformers the heavy atom orbitals interact with the -orbital of the ethylene moiety through the bridge group; this leads to a significant delocalization of the HOMO and to a considerable change in its energy. On the other hand, their interaction with the *-orbital in compounds of the C=C-C-Sn-X type is very low and does not favor the delocalization of lower vacant MO. In vinyldistannane the *-orbital is noticeably delocalized, due to the interaction with the *_Sn-Sn orbital in planar and with the *_Sn-Sn orbital in nonplanar conformers.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 636–641, March, 1992.     

The sodium D2-line in electric and magnetic fields

The influence of perpendicularly crossed electric and magnetic fields of comparable strength on the hyperfine components of the sodium D₂-line was studied by means of laser-atomic-beam spectroscopy. The observed spectra show changes in the polarization type (, ) when one of the fields becomes dominant relative to the other. Theoretical calculations confirm the experimental observations.     

Intensity of the η(C≡C) Bands in the IR Spectra of Acetylene Derivatives and σR 0 Constants of Organosilicon,Organogermanium, and Organotin Substituents

The integral absorptivities of shape-characteristic (CC) bands in the IR spectra of 66 acetylene derivatives RCCX (R = H, Me₃M; X are inorganic and organic substituents) are related by a common linear equation to the _R ⁰ constants of the R and X substituents. The _R R⁰ constants of 10 Alk₃M substituents were calculated. The _R ⁰, _R , and _R ⁺ constants of Me₃M substituents were analyzed. The positive _R ⁰ values (0.12, 0.06, and 0.04 for R = Si, Ge, and Sn, respectively) suggest that in the ground electronic state of Me₃MCCX molecules the resonance acceptor effect of the Me₃M substituents (d, conjugation) prevails over donor (, conjugation). The first effect attenuates and the second enhances as the atomic number of M increases.     

σ-π separation: Excited H2 as a model system

The low-lying states of H₂ consist of one core () and one valence () electron and afford a direct evaluation of intershell - interaction. After resolution of the electronic energy into only, only, and - parts, it is shown that an electronic change in this model system is due solely to a change in the electrons. Simple Hückel theory is examined. If the molecular core is represented properly, regardless of the wave function the calculated and parameters are in reasonable agreement with the empirical parameters. This agreement appears to be due to a fortuitous cancellation of energy contributions.

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Zusammenfassung Die niedrig liegenden -Zustände des H₂ bestehen aus einem Rumpfelektron und einem Valenzelektron und ermöglichen eine direkte Auswertung der --Wechselwirkung zwischen zwei Schalen. Nach der Zerlegung der elektronischen Energie in -,- und --Anteile wird gezeigt, daß eine elektronische Veränderung in diesem Modellsystem nur auf eine Veränderung des -Elektronenanteils zurückgeht. Die einfache Hückeltheorie wird untersucht. Wenn der Molekülrumpf geeignet dargestellt wird, so sind, unabhängig von der -Wellenfunktion, die berechneten Parameter und in guter Übereinstimmung mit den empirischen Parametern. Diese Übereinstimmung scheint auf eine starke Auslöschung von Energieanteilen zurückzugehen.

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Résumé Les états inférieurs de H₂ consistent en un électron de coeur () et un électron de valence () et fournissent une évaluation directe de l'interaction entre couches -. Après expression de l'énergie électronique en parties , et -, on montre qu'une modification électronique de ce système modèle est due seulement à une modification des électrons . La théorie de Hückel simple est examinée. Si le coeur moléculaire est convenablement représenté, quelle que soit la fonction d'onde , les paramètres at calculés sont en accord raisonnable avec les paramètres empiriques. Cet accord apparaît comme le résultat d'une compensation fortuite de contributions énergétiques.

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Work performed in part under the auspices of the U.S. Atomic Energy Commission.

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Work aided by the U.S. Public Health Service via grant GM 08068.     

Calculation of two-center zero-field splitting integrals

Two-center zero-field splitting (ZFS) integrals have been calculated by numerical integration of Coulomb repulsion integrals which are evaluated over basic charge distributions as defined by Roothaan in terms of Slater atomic orbitals. The method is applied to the calculation of the ZFS integrals for -, - and - electron interactions on C, N and N⁺ centers. Numerical results are given.

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Zusammenfassung Zweizentren ZFS-Integrale sind mittels numerischer Integration von Coulombintegralen berechnet worden, und zwar die -, -- und --Integrale an C-, N- und N⁺-Zentren. Die numerischen Resultate werden mitgeteilt.

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Résumé Les intégrales bi-centriques de séparation à champ nul (ZFS) ont été calculées par intégration numérique des intégrales de répulsion coulombiennes évaluées pour les distributions de charge fondamentales définies par Roothan en termes d'orbitales atomiques de Slater. La méthode est appliquée au calcul des intégrales ZFS pour les interactions -, - et - sur les centres C, N et N⁺. Résultats numériques.

     

Hyperconjugation of unsymmetrical groups

The interaction of the -bond system with the -electron system in molecules of type {ie427-01} is easily determined for the symmetrical CH₃ group by isolating the -component from the system of three -bonds; CH₃ is thus treated as a C=X quasivinyl group. The theory is extended to unsymmetrical groups.Read at the Symposium on Quantum Chemistry, Palanga, June 1965.     

Calculation of σ→π* and π→σ* transitions in vinylboranes

Calculations are presented of the energies of the ground and excited and electronic states of ethylene and substituted vinylboranes. The Pople-Segal-Santry method was employed throughout. It is concluded that the excited state of lowest energy in ethylene has * character whilst the lowest energy ultra-violet spectral bands of the latter compounds stem from ^* transitions.

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Zusammenfassung Valenzelektronenrechnungen nach Pople-Segal-Santry wurden für Äthylen und Vinylborane durchgeführt. Danach hat der niedrigste angeregte Zustand von Äthylen ^*-Charakter, während die längstwellige UV-Bande der Vinylborane einem ^* -Übergang entspricht.

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Résumé Calculs de l'énergie pour les états fondamentaux et excités et de l'éthylène et des vinylboranes substitués. Utilisation de la méthode de Pople-Ségal-Santry. L'état excité le plus bas pour l'éthylène résulte d'une transition ^* , alors qu'il résulte d'une transition ^* pour les vinylboranes.

     

Investigation of the electronic effect of the diphenylphosphino group

We have synthesized meta-substituted derivatives of benzoic acid, determined their ionization constants in water-alcohol solutions of concentration 11 and 14 by volume, and calculated the Hammett constant _m of the diphenylphosphino (0.12), diphenylamino (–0.04), diphenylphosphinyl (0.40) and diphenylthiophosphinyl (0.32) groups. Unlike the diphenylamine group, the diphenylphosphino group is metaorienting, which is probably to be explained by the absence or the weak nature of p- conjugation of incomplete electron pairs on the phosphorus and the presence of an electron-acceptor effect (d-p conjugation).