Leapfrog fullerenes, Hückel bond order and Kekulé structures

Abstract

Investigation of a sample of 5436 fullerene isomers indicates a relationship between Kekulé structures and the molecular orbital theory of these trivalent cages. In leapfrog fullerenes (those constructed by omnicapping and dualising a fullerene parent), the edges of maximal Hückel π bond order define the Kekulé structure with the maximum number of benzenoid hexagons (the Fries structure). For general fullerenes, the bond orders rarely correspond exactly to a Kekulé structure: of 1812 C₆₀ fullerene isomers, for example, only 23 have a Hückel Kekulé structure.