A combination of Clar number and Kekulé count as an indicator of relative stability of fullerene isomers of C60

Abstract

Kekule count is not as useful in predicting the thermodynamic stability of fullerenes as it is for benzenoid hydrocarbons. For example, the Kekule count of the icosahedral C60, the most stable fullerene molecule, is surpassed by its 20 fullerene isomers (Austin et al. in Chem Phys Lett 228:478–484, 1994). This article investigates the role of Clar number in predicting the stability of fullerenes from Clar’s ideas in benzenoids. We find that the experimentally characterized fullerenes attain the maximum Clar numbers among their fullerene isomers. Our computations show that among the 18 fullerene isomers of C60 achieving the maximum Clar number (8), the icosahedral C60 has the largest Kekule count. Hence, for fullerene isomers of C60, a combination of Clar number and Kekule count predicts the most stable isomer.