The quantum chemical investigations of some representative bis-adducts of C60, C60O2, C60（NH）2, C60（CH2NHCH2）2 and C60（SO4）2 have been carried out at the AM1 and PM3 semi-empirical molecular orbital levels. The relative energies of various isomers of these C60 bis-adducts have been calculated. For C60O2 and C60（NH）2 with the sterically non-demanding addends, cis-1 isomer resulted from 1,2-additions to adjacent 6/6 ring fusion is the lowest energy structure; for C60（CH2NHCH2）2 and C60（SO4）2 with sterically demanding addends, the most energetically preferred structure is e isomer. This is consistent with and enhances the general rule for regio-selectivity of fullerene C60 established by Hirsch, though Hirschs rule is summarized on the basis of methanofullerenes. The thermodynamic analysis is not significant to explain the experimentally observed regiochemistry for C60 bis-adducts, and the kinetic reasons or mechanisms may dominant in determining the regioselectivity of fullerene bis-adducts. Further addition patterns for multiple addition were also discussed.
