A THEORETICAL-STUDY OF C-60, C-76 AND C-84 FULLERENES AND THEIR ISOMERIC REARRANGEMENT MECHANISMS BY SEMIEMPIRICAL METHODS

We present the results of a semiempirical study of C-60 (I-h, D-6h, C- 3v, C-3, D-5) C-76 (T-d, D-2, C-3) and C-84 (T-d, C-3, C-3v) fullerene s and their isomer skeletal rearrangements. We have proposed four diff erent intramolecular rearrangements in the fullerenes. The interconver sion between two isomeric fullerene are carried out by these intramole cular rearrangements. The 2-D Schlegel diagrams with symmetry analysis for fullerenes are used to find the possible reaction mechanism in th e geometry interconversion. We use semiempirical methods MNDO and MM2 (which are implemented in Spartan 3.1 program) to compute the heats of formation, steric strain energy, electronic structure and Delta epsil on (HOMO-LUMO) for these carbon cages. Estimates are presented for act ivation energy and enthalpy change of isomerization. The transition st ates in the reaction are also generated. The results suggest that C-60 (I-h), C-76(D-2) and C-84(D-6h) are the global minimum structure of C- 60 (7 isomers), C-76 (3 isomers), and C(8)4 (3 isomers) respectively.