Partition of 𝜋–electrons in rings of double linear hexagonal chains

Abstract

Two methods for assessing the π-electron content of a ring of a benzenoid hydrocarbon were recently proposed: one based on the averaging of the π-electron contents of the Kekulé structural formulas, and the other based on an analogous treatment of the Clar aromatic sextet formulas. We apply these two methods to the homologous series consisting of two condensed linear polyacene units (whose first members are pyrene, anthanthrene, peri-naphthacenonaphthacene, ...). The two approaches give essentially the same results. Contrary to the case of linear polyacenes (in which the partition of π-electrons into rings is uniform), in their double-chain analogs the partition of π-electrons is found to be highly non-uniform. The electron contents monotonically decrease along each polyacene chain, being maximal in the hexagons having the smallest number (= 2) of neighbors. Several other regularities of the π-electron distribution are also established.