RELATIVE STABILITIES OF C-76 ISOMERS - A NUMERICAL TEST OF THE FULLERENE ISOLATED-PENTAGON RULE

C76 has 19151 possible fullerene structural isomers of which up to 5 5 are compatible with the experimental 19-line C-13 NMR spectrum, but only two have isolated pentagons. Calculations of the relative energies of all 55 candidates within the semi-empirical QCFF/PI model pick out the isolated-pentagon D2 isomer as the structure of lowest energy for C76, confirming previous calculations and providing support for the isolated-pentagon rule. Energy differences between isomers of C76 are interpreted in the model as torsional strains induced by pentagon adjacencies.