Energetics and isomerisation pathways of a lower fullerene. The Stone–Wales map for C 40

Graph-theoretical and semi-empirical quantum-chemical results are combined to give a picture of the energetics and isomerisations of a typical lower fullerene, C40. 38 of the 40 distinct fullerene isomers of C40 are connected by Stone–Wales (pyracylene) transformations; the isomer of lowest total energy (as calculated by the QCFF/PI method) has the smallest number of fused pentagon pairs, and elimination of pentagon adjacencies by successive pyracylene rearrangements takes all other connected C40 fullerenes downhill to the optimal isomer.