Homoheteroaromaticity: the case study of azepine and dibenzazepine.

Geometrical and energetic DFT calculations as well as GIAO and NICS chemical shifts have been calculated for 1H-azepine and 5H-dibenz[b,f]azepine and their cations. The last compound has been studied experimentally by 1H and 13C NMR in neutral and acidic conditions establishing that the cation corresponds to an N-protonated structure. The conclusion is that the neutral molecules are antiaromatic while the cations are aromatic (homoheteroaromaticity).