AbstractWe present the results of a semiempirical study of C₆₀ (I_h, D_6h, C_3v, C₃, D₅), C₇₆ (T_d, D₂, C₃) and C₈₄, (T_d, C₃, C_3v) fullerenes and their isomer skeletal rearrangements. We have proposed four different intramolecular rearrangements in the fullerenes. The interconversion between two isomeric fullerene are carried out by these intramolecular rearrangements. The 2-D Schlegel diagrams with symmetry analysis for fullerenes are used to find the possible reaction mechanism in the 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 Δɛ (HOMO-LUMO) for these carbon cages. Estimates are presented for activation energy and enthalpy change of isomerization. The transition states in the reaction are also generated. The results suggest that C₆₀I_h), C₇₆(D₂) and C₈₄ (D_6h) are the global minimum structure of C₆₀ (7 isomers), C₇₆, (3 isomers), and C₈₄ (3 isomers) respectively.