ELECTRONIC AND GEOMETRICAL STRUCTURE OF H2B-O-BH2 - AN AB-INITIO STUDY

The structure of the diboroxane H2B-O-BH2 has been studied by means of ab initio calculations at the MP4/6-311G(*)//MP2/6-311G(**) level. T wo minima have been characterized on the potential energy surface (PES ): one is of D-2d symmetry, analogous to the isoelectronic allene mole cule, and the other is of C-2v symmetry, lying 0.6 kcal/mol lower in e nergy than the D-2d one. The D-2h structure lies 11.3 kcal mol(-1) abo ve the absolute minimum and is a peak on the PES (two imaginary freque ncies). The preference for a bent structure of C-2v symmetry is ration alized through an orbital analysis. A reaction path between the two mi nima has been computed and may be described as a conrotatory motion of the two BH2 planes, coupled with the BOB angle opening. The associate d activation energy is 1.2 kcal mol(-1). These results are discussed i n light of the experimental data on substituted R(2)B-O-BR(2) diboroxa nes.