Theoretical studies on the stabilities of some C-60 bis-adducts

The quantum chemical investigations of some representative bis-adducts of C -60, C-60 O-2, C-60(NH)(2), C-60(CH2NHCH2)(2) and C-60(SO4)(2) have been ca rried out at the AM1 and PM3 semi-empirical molecular orbital levels. The r elative energies of various isomers of these Cs, bis-adducts have been calc ulated. For C60O2 and C-60(NH)(2) with the sterically non-demanding addends , cis-1 isomer resulted from 1,2-additions to adjacent 6/6 ring fusion is t he lowest energy structure; for C-60(CH2NHCH2)(2) and C-60 (SO4)(2) with st erically demanding addends, the most energetically preferred structure is e isomer. This is consistent with and enhances the general rule for regio-se lectivity of fullerene C-60 established by Hirsch, though Hirsch's rule is summarized on the basis of methanofullerenes. The thermodynamic analysis is not significant to explain the experimentally observed regiochemistry for C-60 bis-adducts, and the kinetic reasons or mechanisms may dominant in det ermining the regioselectivity of fullerene bis-adducts, Further addition pa tterns for multiple addition were also discussed.