Analysis of conformation composition of tetra- and pentamethyl substituted of 1,3,2-dioxa(oxaza)borynanes

The calculation of energy with full optimization of geometry of the 2,4,4,6- and 2,4,6,6-tetramethyl- and also 2,4,4,6,6-pentamethyl-1,3,2-dioxa(oxaza)borynanes is carried out by means of empirical (MM2) and semiempirical (AM1, MNDO) methods. The basic minimum for molecules of tetramethyl-derivatives has a flat form and high occupation of sofa and semi-chair conformers with prevalence of the latter form. Equilibrium between two invertomers of semi-chair is peculiar to the molecules of penta ethyl-derivatives. Obtained data offer essentially add conformation referrals of cyclic boric esters on the base of NMR data and open addition abilities for prediction of conformation composition of molecules in these compounds