On the Hall rule in the theory of benzenoid hydrocarbons

In 1973, Hall noticed that the total pi-electron energy (E) of isomeric benzenoid hydrocarbons is a linear function of the number of Kekule structures (K). Since then, this remarkable rule has been confirmed on a plethora of examples. Twenty years later, it was discovered that for large benzenoids (with nine or more hexagons) the E-K dependence is slightly curvilinear. We now elaborate a novel approach, describing and, to some extent, rationalizing these peculiar features of the E-K dependence. (C) 1999 John Wiley & Sons, Inc.