Density functional studies of the stepwise substitution of pyridine, pyridazine, pyrimidine, pyrazine, and 1,3,5-triazine with BCO.

The structures, stabilities, and aromaticities of a series of (BCO) n (CH)5-n N (n = 0-5), (BCO) n (CH)4-n N2 (n = 0-4), and 1,3,5-(BCO) n (CH)3-n N3 (n = 0-3) clusters were investigated at the B3LYP density functional level of theory. The most stable positional isomers of individual clusters were obtained. All of the calculated CO binding energies were positive, suggesting that the BCO-substituted species are stable. It was found that the BCO-substituted structures are much less strained than their carbocation counterparts. The negative nucleus-independent chemical shifts (NICSs) obtained show that all of the BCO-substituted species possess three-dimensional aromaticity, in good accord with the aromaticities of the corresponding hydrocarbon species.