Conformational analysis of stereoisomers of 4,5-dimethyl-1,3,2-dioxaborinane

Empirical (MM2) and semiempirical (AM1, MNDO) calculations with full geomet ry optimization were used to calculate the energies of cis- and trans-4,5-d imethyl-1,3, 2-dioxaborinanes. Comparison of the experimental and calculate d spin-spin coupling constants and energies of the conformers shows that ci s-4,5-dimethyl-1,3,2-dioxaborinane exists as a multicomponent equilibrial s ystem with appreciable contributions of the sofa and half-chair conformers with axial and pseudoaxial orientations of the methyl group on C-4. The tra ns isomer predominantly exists as a sofa conformer with a possible admixtur e of half-chair forms.