Theoretical Studies of Growth Mechanism of Small Fullerene Cage C24 (D6d)

The ring-collapse mechanism of C24 (D6d) has been analyzed using semiempirical AM1 and B3LYP/cc-pVDZ methods. Based on the ring-stacking/circumscribing model, two precursors are selected. Transition states and intermediates are located and energetics are computed. Before the stacking begins, the precursor and belt reach a suitable relative orientation accompanied by the release of a large amount of energy. It is observed that the reactions between the precursors and the belts are essentially endoergic in nature, whereas the reactions between the stable intermediates and the final belts are exoergic. The deformation energies (DE) and the bond lengths R of the precursors have been computed. The DE values suggest that there is a chance of the cleavage of the bicyclic precursors as the growth process proceeds toward the cage formation. In contrast, the monocyclic precursor is found to have lower deformation energies than the bicyclic precursor. Analysis of average bond length at different cages shows that a large window is formed and the system appears to follow a cascade-type bond formation. Comparisons are made to our previous results on C28 growth. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem 103: 355–368, 2005