An ab initio valence bond (VB) calculation of the π delocalization energy in borazine, B3N3H6

Valence bond (VB) calculations using a double-zeta D95 basis set have been performed for borazine, B3N3H6 and for benzene, C6H6 in order to determine the relative weights of individual standard Lewis structures. In the delocalized resonance scheme of borazine, the structure (1) with no double bonds and three lone pairs of electrons at the three nitrogen atoms is the major contributor with a structural weight of 0.17, followed by six equivalent Lewis structures with one double bond and two lone pairs at two nitrogen atoms (11) with weights of 0.08 each. In the case of benzene, the two Kekule structures (111) contribute with structural weights of 0.15 each, followed by 12 equivalent ionic structures (IV) with weights of 0.03 each, followed by the three equivalent Dewar-type structures (V) with structural weights of 0.02 each. The values of 54.1 and 45.8 kcal mol(-1) for the delocalization energies of borazine and benzene were estimated. Therefore, B3N3H6 is calculated to have substantial aromatic character, similar to benzene, when we assume that the resonance energy can provide a criterion for aromaticity. (c) 2005 Wiley Periodicals, Inc.