Search

The mechanism of reactions of silatranes and germatranes, and their bicyclic and monocyclic analogues with one molecule of methanol or ethanol, was studied at the Density Functional Theory (DFT) B3PW91/6-311++G(df,p) level of theory. Reactions of 1-substituted sil(germ)atranes, 2,2-disubstituted sil(germ)ocanes, and 1,1,1-trisubstituted hyposil(germ)atranes with alcohol (methanol, ethanol) proceed in one step through four-center transition states followed by the opening of a silicon or germanium skeleton and the formation of products. According to quantum chemical calculations, the activation energies and Gibbs energies of activation of reactions with methanol and ethanol are close, their values decrease in the series of atranes&ndash, ocanes&ndash, hypoatranes for interactions with both methanol and ethanol. The reactions of germanium-containing derivatives are characterized by lower activation energies in comparison with the reactions of corresponding silicon-containing compounds. The annular configurations of the product molecules with electronegative substituents are stabilized by the transannular N&rarr, X (X = Si, Ge) bond and different intramolecular hydrogen contacts with the participation of heteroatoms of substituents at the silicon or germanium.

The mechanism of the hydrolysis reactions of 2,2-dihydroxysilocane, 2,2-dihydroxygermocane, 1-hydroxysilatrane, and 1-hydroxygermatrane was studied by the density functional theory method. Accordin...

Conformational analysis of tris(2-pyridyl)phosphine and tris(2-pyridyl)phosphine chalcogenides was carried out by the method of dipole moments and density functional theory calculations. The conformations of the examined compounds fit into the overall conformational picture for the P III and P IV compounds: namely, these phosphines have non-eclipsed gauche- and trans -forms with propeller arrangement of the pyridyl radicals about the P = Y bond (Y = lone pair, O, S, Se).

The structure of some six- and eight-membered phosphorus and silicon heterocycles was established by the method of dipole moments and density functional theory calculations. There are two necessary conditions for the feasibility of the transannular interaction in these heterocycles: (1) the favorable disposition of the donor and acceptor centers in a molecule and (2) the presence of the substituents with the considerable polarizing effect at the heteroatom.

Experimental and theoretical conformational analysis of polyfunctional 2-substituted nitroethenes was carried out by the method of dipole moments and density functional theory calculations. It was established that the nitro and ester (or trichloromethyl) groups are trans-arranged in the molecules of 2-trichloromethyl-(ethoxycarbonyl)-1-nitro- and 1-bromo-1-nitroethenes, i.e., nitroalkenes have E-configuration, their bromo-containing analogues have Z-configuration, and s-cis-orientation of the C=C and C=O double bonds is preferred for nitroacrylates. 2,3-Dibromo-3-nitroacrylates have untrivial Z-configuration in solution.

The structure of silatranes N[CH 2 (RMeC 6 H 2 )O] 3 SiR 1 with planar fragments in six-membered semi-rings was established by the methods of dipole moments and density functional theory calculations. They are endo-structures with transannular interaction N → Si in which the oxygen atoms located adjacent to the silicon participate besides the nitrogen and silicon atoms.

Structure of 1,4-heterophosphinanes in solution was studied by the methods of dipole moments, Kerr effect, molecular mechanics, and density functional theory calculations. It was determined that chair conformation with an equatorial orientation of the exocyclic phenyl substituent is preferred for 1,4-heterophosphinanes independent of the second heteroatom in six-membered phosphorus heterocycle (oxygen, sulfur or silicon), and the coordination state of the phosphorus atom (σ3P or σ4P).