Vindicating the Pauling-bond-order concept

In the Pauling-bond-order concept, it is assumed that all Kekule structures of a benzenoid molecule contribute equally to the pi-electron contents of the carbon-carbon bonds. We modified the Pauling-bond-order: (a) by increasing the weight of a Kekule structure proportional to the number of Fries-type hexagons and (b) by increasing the weights of the Kekule structures that are compatible with Clar aromatic sextet formulas. Improvements in reproducing experimental carbon-carbon bond lengths are insignificant, implying that equal weighting of Kekule structures is more justified than one could anticipate. (c) 2006 Elsevier B.V. All rights reserved.