Contribution of the Scientific School of Academician M.G. Voronkov to the Development of the Chemistry of Biologically Active Atranes (Protatranes and Hydrometallatranes) (A Review).

The main results of the many years' studies of the scientific school of Academician Mikhail G. Voronkov in the field of two subgroups of the atrane family (protatranes and hydrometallatranes) as well as the results of research in continuation of the studies initiated by Academician M. G. Voronkov have been summarized and presented. Long-term studies of atranes under the leadership of M. G. Voronkov have led to the discovery of their unique biological activity and the creation of a series of unique original drugs and means of agricultural chemicalization: biostimulants and adaptogens for agricultural plants, animals, useful insects and microorganisms.

Rearrangements of [C(6)H(7)Si](+) cations. A radiochemical and quantum chemical study.

Nucleogenic cations were formed by beta-decay of phenylsilane tritiated at ortho- and para-positions of the benzene ring as well as at the silyl group and the products of their reactions with methyl tert-butyl ether were analyzed by radiochromatography. We found that the o-silatolyl cation was isomerized into the silabenzyl cation while the p-silatolyl cation was not. Furthermore, the silabenzyl cation was not converted into other isomers. The potential energy surface of the C(6)H(7)Si(+) system was constructed by B3LYP and MP2 methods using an aug-cc-pVDZ basis set. Theory predicts the low barrier for o-silatolyl-silabenzyl isomerization but high barriers for hydride shifts in the ring from para to meta- to ortho-isomers. It seems that nascent nucleogenic ions have enough internal energy to overcome the ortho-to-benzyl barrier but not enough to cross over the hydride-shift barriers. Theory also confirms that the isomerization of the silabenzyl cation to the [C(6)H(6).SiH](+) complex takes place in one step with a 62 kcal mol(-1) barrier, whereas that to either the global minimum [C(6)H(7).Si](+) or the silatropylium ion involves multisteps with 69-80 kcal/mol barriers. In addition, we find that the barrier of interconversion between the [C(6)H(6).SiH](+) complex and one of the low-lying [C(6)H(7).Si](+) complexes is only 29 kcal/mol.