Some Observations on the Topological Resonance Energy of Benzenoid Hydrocarbons*

Two empirical rules are formulated for the topological resonance energy (TRE) of benzenoid hydrocarbons: (a) TRE is roughly linear function of the number of Kekule structures, and (b) in a homologous series containing a linear polyacene fragment, TRE is a linear function of the length of this fragment. In certain cases, however, the TRE model leads to incorrect predictions. There exist pairs of isomeric benzenoid hydrocarbons, in which the isomer with a greater number of Kekule structures has smaller TRE. The present study indicates that the TRE model needs to be critically revised.