Topological "in-out" isomerism in perhydrogenated fullerenes revisited. (C60H58RR2)-R-1 with two R groups "in" (R-1, R-2 = H, Me)

Molecular mechanics calculations (using MM+, MMX and AMBER force fields) of all constitutional and topological isomers of (C60H58RR2)-R-1 with R-1, R- 2 = H, Me revealed that "in,in" isomers are always the most stable, while t ime corresponding "'out,out" isomers have the biggest energy. Moreover, a s ubstitution of an "in" hydrogen atom by a methyl group in the confined volu me of the C-60 cage does not change, or even towers, the steric energy. The dependence of steric energy on the distance between the "in" hydrogen atom s (or between the carbon atoms of "in" methyl groups) reveals highly irregu lar behaviour, for close neighbours, reflecting differences in the energies associated with considerable distortions of the fullerane skeleton.