Relation between electron and energy contents of hexagons in pericondensed benzenoid hydrocarbons

Abstract

Relations are established between the π-electron content (EC) and the π-electron energy electron energy content (ec) of hexagons in pericondensed benzenoid hydrocarbons. Whereas in catacondensed benzenoids only four types of differen tly annelated hexagons need to be distinguished [Furtula, Gutman & Turkovic, Indian J Chem 43A (2004)], in pericondensed systems there are 12 different annelation types. We show that within each of the 12 classes of equally annelated hexagons there exists a linear correlation between EC and ec. These correlations can be explained by means of the Cruickshank-Sparks equations, which relate the Pauling and Coulson bond orders. In addition, within each annelation class there is a correlation between the ec-value of a hexagon and the effect ef of the same hexagon on the total π-electron energy of the corresponding benzenoid molecule. Most of these latter correlations are curvilinear. Our main conclusions are that (a) ec is proportional to EC and (b) ec is proportional to ef, but (c) the mode of the annelation of the respective hexagon strongly influences the actual form of these interdependencies.