Oemo analysis of ab inttio scf—mo computations. conformational preferences and asymmetries in methyl derivatives

A procedure is described which allows analysis of ab initio SCF—MO results in the framework of an OEMO model, in terms of total energy and a PMO quantitative approach. The procedure is applied to the analysis of the effects of non-bonded interactions upon the conformational preferences of molecules of the type CH₃—X (with X = CH₃, NH₂, OH). The use of a basis of fragment localized MO's allows discussion of the energy effects in terms of bond—bond and bond—lone pair repulsions and conjugative stabilizations. It is found that the non-bonded interactions are responsible for the conformational preference and the rotational barrier in these molecules: in all cases the optimum conformation is characterized by the smallest bond—bond repulsion and the largest conjugative stabilization. The factors determining the asymmetries of the methyl groups in methylamine and methanol have also been investigated.