A mathematical model, referred here as the Zhang-Zhang polynomial xi(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 xi(x) is related to resonance energy, and that In xi(x) and RE are best correlated when x approximate to 1. This indicates that xi(1) could be viewed as a (novel) structure-descriptor, playing a role analogous to the Kekule structure count in Kekule-structure-based theories. Some basic properties of xi(1) are established. (c) 2005 Elsevier B.V. All rights reserved.