A Clar-Type Regularity for Dianions of Benzenoid Hydrocarbons

Abstract

Phenanthreno-annelated anthracenes as well as their dianions are studied by means of molecular-orbital theory (at the AM1 level). The charge distribution in the dianions is highly non-uniform: the anthracene fragment bears roughly 50% more negative charge than the phenanthrene fragment(s). These findings point at the possibility to apply the concepts of Clar aromatic sextet theory to benzenoid dianions. Within the framework of this Clar-type model, phenanthreno-annelated anthracene dianions may be viewed as charged analogs of all-benzenoid hydrocarbons.