SCF MO LCAO has been used in the CNDO/2 approximation to determine the valence states for borine and nitrogen in substituted phenazaborines containing 3-coordinated and 4-coordinated boron atoms. In the first case, the heterocyclic electron structure has donor-acceptor interaction for the heteroatom π orbitals via the π-electron system in the phenylene groups and substantial conjugation of the latter via the heteroatom π orbitals. In the second, those effects are much weaker and the heterocycle has a nonplanar structure. The valence index VB(4) for the 4-coordinated B(4) does not exceed VB(3).
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