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Molecular modeling methods were employed to investigate the potential energy surface in the valence isomerization of bis(5-thioxopenta-1,3-dien-1-yl) sulfide initiated by generation of thiirane and thiophene biradical structures in the lowest triplet state. The channel of the cascade formation of condensed systems containing the thiirane and polycyclobutane fragments was analyzed. [ABSTRACT FROM AUTHOR]

This paper reports on our quantum-chemical analysis of the nucleophilic substitution of the bromine atom by the cyano group in the reaction of methylbromoacetylene with copper cyanide. According to calculations, the reaction can form a four-membered ring containing a copper atom. [ABSTRACT FROM AUTHOR]

The potential surfaces of (2π + 2π) cyclization of bis(3-thioxo-1-propenyl) sulfide in the S 0, T 1, and S 1 states were studied using quantum-chemical methods of molecular simulation. In the S 0 and S 1 states, the cyclization yields a thiabicyclic structure. In the T 1 state, three cyclization pathways yielding thiabicyclic, thiirane, or thiophene structure are possible. [ABSTRACT FROM AUTHOR]

Quantum chemical methods were used to investigate the mechanism of interaction of polyhydrated Hg(II) with methylcobalamin — a derivative of vitamin B12. Migration of the methyl group in the B12·Hg(II) nH2O cluster, initiating the formation of methylmercury, is considered. The reaction of substitution of methylmercury for the cobalt atom in the corrin fragment of B12 has been studied. The thermodynamic and activation characteristics of these processes have been obtained. The mercury analog of vitamin B12 is shown to exist in two radically different conformations. [ABSTRACT FROM AUTHOR]

A quantum chemical study of structural peculiarities of iminodihydrofuran ensembles (from dimers to tetramers with individual calculations for penta- and hexamers) associated with their rotation isomerism was carried out. Three basic spatial packings of the iminodihydrofuran chains were distinguished with increasing the number of ensemble elements. The spiral and linear packings are equally probable from the standpoint of their thermodynamic stability. The third packing, exhibiting the curvature radius, is inferior to the former two, as judged from the relative stability. It was shown that ensembles in the alternating linear-spiral form are fundamentally possible to exist. Data was obtained testifying to a possibility for the intramolecular hydrogen bond forming between the imine and amine moieties in the tetramer spiral structures; activation barriers of intramolecular prototropic rearrangement were determined. [ABSTRACT FROM AUTHOR]

Quantum chemical methods were used to investigate the mechanism of interaction of polyhydrated Hg(II) with methylcobalamin — a derivative of vitamin B12. Migration of the methyl group in the B12·Hg(II) nH2O cluster, initiating the formation of methylmercury, is considered. The reaction of substitution of methylmercury for the cobalt atom in the corrin fragment of B12 has been studied. The thermodynamic and activation characteristics of these processes have been obtained. The mercury analog of vitamin B12 is shown to exist in two radically different conformations. [ABSTRACT FROM AUTHOR]