Local aromaticity in benzo- and benzocyclobutadieno-annelated anthracenes

Abstract

Considerations based on the energetics of cyclic conjugation in individual rings indicate that benzocyclobutadieno-annelation has the opposite effect on local aromaticity in benzenoid hydrocarbons to benzo-annelation. This finding is now tested and corroborated by density functional theory (DFT) calculations of the geometry of all benzo- and benzocyclobutadieno-annelated congeners of anthracene. The harmonic oscillator model of aromaticity (HOMA) and some similar (geometry-based) indices of local aromaticity are found to have the same dependence on the modes of annelation as the molecular-graph-based energy effects.