COMPARISON OF PI-BOND STRENGTHS IN M-E (M=B, AL, GA, E=O, N, S) COMPOUNDS - AB-INITIO CALCULATION OF ROTATIONAL BARRIERS

Results of ab initio calculations of the electronic structure of compo unds of the type R(2)MER'(x) and R(2)MEMR'(2) with R = H, Me, M = Al, Ga, and E = O, N, S are reported at the Hartree-Fock level with split- valence, polarization basis sets for all atoms except hydrogen where a split-valence basis set is used. Full optimizations for the equilibri um geometry and partial optimization at constrained rotational transit ion states have been performed to evaluate the barriers to rotation as a measure of the pi interactions in these compounds. We conclude that , although important for determining the final conformational equilibr ium geometries, pi interactions are weak in these compounds as the rot ational barriers are smaller than that for ethylene by 1 or 2 orders o f magnitude.