AN ANALYSIS OF THE 63 POSSIBLE ISOMERS OF C60H36 CONTAINING A THREEFOLD AXIS - A NEW STRUCTURE FOR C60H20

The structures and stabilities of all 63 isomers of C60H36, in which p airs of hydrogen atoms occupy the hex-hex edges of the truncated icosa hedron and in which there is at least one three-fold axis, have been c alculated. The two most stable structures, of T and D-3d symmetry, are based on C18H18 crowns and have been described previously. A statisti cal analysis of the heats of formation as a function of the 12 types o f polyhedral face which may be present in each structure shows that C6 H4 (or C-6 which are equivalent in this case), 1,2,3-C5H3, 1,2-C5H2 an d C5H rings are particularly stabilising, whereas C6H6 and C5H5 rings are particularly destabilising. Extension of this analysis shows enhan ced stability is achieved by the edge sharing of C-6 and 1,2,3-C5H3 ri ngs. These indications of stabilising features have led to postulation of structures of other C60Hn molecules. One of these, a D-5d belt str ucture of C60H20, is slightly more stable than any found previously.