Cyclic conjugation in terminally bent and branched phenylenes

Cyclic conjugation in terminally bent and branched phenylenes is studied by means of the effect that individual cycles have on total π-electron energy. These energy-effects are computed by a molecular-orbital approach. The hexagonal squeezes of the phenylenes examined are benzo-annelated polyacenes. A general regularity for the intensity of cyclic conjugation is found. In the linear part of the molecule, cyclic conjugation follows a pattern analogous to that in the hexagonal squeeze (Clar-type regularity); in the bent or branched parts of the molecule, the intensity of cyclic conjugation is inverse to what exists in the hexagonal squeeze (anti-Clar-type regularity).