Structural aspects of the aromaticity of cyclic π-electron systems with BN bonds

An extension of the HOMA model and Bird's I-6 model for systems with B-N bonds is given. Analysis of the aromatic character of 11 pairs of borazine derivatives and their benzene analogues is done based on Cambridge Structural Database (CSD) release using HOMA and I-6 indices. Borazine derivatives exhibit less aromatic character than their benzene analogues and are much less sensitive to the chemical and topological effects from the environment of the rings in question. In contrast to cyclooctatetraene, 1,3,5,7-tetra-t-butyl-2,4,6,8-tetramethyl-1,3,5,7,2,4,6,8-tetraazatetraborocine does not exhibit antiaromatic character. (C) 1998 Elsevier Science Ltd. All rights reserved.