The relative reactivity of the two kind of bonds in C60 and the eight kind of bonds in C70 has been systematically explored using M06-2X functional.1 To this end,the Diels-Alder cycloadditions of trans-1,3-butadiene to C60 and C70 were analyzed from the thermodynamics viewpoint.The distortion and interaction energy model was utilized to elucidate the origin of the different reactivity.2 Other issues,such as the pyramidilaztion angles,3 the frontier molecular orbitals,the electrostatic potential surfaces of the corresponding stationary points were also considered.The results showed that the regioselectivity observed in experiment is majorly controlled by the different reactivity of the bonds.This can be understood from the lower activation barrier of the 6-6 bond reaction and the a-b bond reaction.The lower activation barrier originates mainly from larger average pyramidilaztion angles,adaptable symmetry of the frontier orbitals,and more stabilizing interaction energy.The solvent effects on the reaction mechanism were examined using the continuum solvent model.