Structures, vibrational frequencies and polarizabilities of diazaborinines, triazadiborinines, azaboroles, and oxazaboroles

Ab initio, second-order, Moller-Plesset perturbation theory calculations of the equilibrium geometries, harmonic vibrational frequencies, relative sta bilities, dipole moments, and static dipole polarizabilities are reported f or 70 different 6 pi-electron monocycles containing boron and nitrogen. The se include 26 azaborinines isosteric to pyridine, 16 azaboroles, and 28 oxa zaboroles. The most stable isomers have the substructure XBHNH, where X = N , NH, or O is the base-ring heteroatom. Planar conformations are stable min ima for all but 15 five-membered rings. Lower level calculations are unreli able in predicting which molecules are planar. Good agreement is found with the available electron diffraction and X-ray structures of substituted rin gs. Additive atom and bond polarizability models which are accurate to with in a few percent are constructed for a larger set of 104 planar molecules, including azines, azoles, oxazoles, and azaborinines isosteric to benzene. The presence of boron causes scatter od the polarizabilities of isomers; he nce the additive models of polarizability are less accurate than if only he terocycles containing C, N, and O are included.