Clar theory and resonance energy

A mathematical model, referred here as the Zhang–Zhang polynomial ζ(x), that embraces all the main concepts encountered in the Clar aromatic sextet theory of benzenoid hydrocarbons, was recently put forward by Zhang and Zhang. We now show that ζ(x) is related to resonance energy, and that ln ζ(x) and RE are best correlated when x ≈ 1. This indicates that ζ(1) could be viewed as a (novel) structure-descriptor, playing a role analogous to the Kekulé structure count in Kekulé-structure-based theories. Some basic properties of ζ(1) are established.