Cyclic conjugation in benzo-annelated polyacenes

Abstract

Conjugation along a particular ring in a polycyclic conjugated molecule can be measured by means of the effect of the ring on total π-electron energy. Using this approach, we have studied cyclic conjugation in mono-, di-, tri- and tetra-benzo polyacenes. The main conclusion of our research is that the Clar aromatic sextet formulas of the benzo-annelated polyacenes provide a reasonable description of their conjugation modes. A few refinements are, however, possible. The extent of cyclic conjugation is found to be minimal in the central region of the polyacene molecule and it monotonically increases towards its two termini. Geminal annelation has an extra increasing effect on cyclic conjugation. Isoarithmic systems are shown to have practically coinciding conjugation modes.