Extended Hückel Theory. III. Compounds of Boron and Nitrogen

Abstract

The extended Hückel theory is applied to compounds of boron and nitrogen, with emphasis placed upon similarities and differences with isoelectronic and isosteric carbon analogs. The barrier to internal rotation in borazane is predicted to be ∼1.5 kcal/mole and the torsional barrier in aminoborane∼10 kcal/mole. The internal charge-transfer nature of the expected electronic transitions is stressed. The highest occupied orbitals in aminoborane and borazine are computed to be σ type, with important consequences for the reactions of these molecules. It is proposed that the accepted valence picture of borazine is incorrect and that in all B–N molecules N is more negative. Stabilization due to nonbonded electrostatic interactions is studied. Predictions are made regarding the geometry of B–N analogs of cyclobutadiene and cyclooctatetraene. Borazine is calculated to be inefficient in transmitting electronic effects. Computations of the relative stabilities of heteroaromatic B–N compounds are made.