AZABORININES - STRUCTURES, VIBRATIONAL FREQUENCIES, AND POLARIZABILITIES

Ab initio second-order Moller-Plesset (MP2) perturbation theory calcul ations of the equilibrium geometries, relative stabilities, harmonic v ibrational frequencies, dipole moments, and static dipole polarizabili ties are reported for all 17 possible azaborinines (commonly called az aborines) of the formula C6-2nH6BnNn, n = 1, 2, 3. Planar conformation s are stable minima for 16 of these molecules; some errors in the lite rature on this point are corrected. The most stable isomers for n = i, 2, and 3 respectively are 1,2-azaborinine, 1,3,2,4-diazadiborinine, a nd borazine. Good agreement is found with available X-ray structures o f substituted azaborinines. The ratio of MP2 to Hartree-Fock (HF) harm onic frequencies is found to vary around an average of 0.95 for this s et of isoelectronic molecules. The polarizabilities of the azaborinine s along with our earlier results for the azoles, oxazoles, and azines constitute a uniform quality data set of polarizabilities for 50 heter oaromatic molecules. Simple empirical formulas based upon atom- and bo nd-additive models correlate the calculated polarizabilities of the 49 planar heteroaromatic rings quite well.