Stereochemical patterns in [76]fullerenes, C 76 to C 76H 28

Abstract

The structures and stabilities of C 76 and various isomers of C 76H n as n increases from 2 to 28 have been calculated using the AM1 Hamiltonian and the program mopac 6.0. C 76 forms an elongated structure with relatively flat areas in which some carbon atoms are at the junction of three six-membered rings. The bonding in some of these graphite-type rings is delocalised whereas in the remainder of the structure the double bonds are localised on edges linking two hexagonal faces. Hydrogenation occurs at these double bonds on the more curved part of the structure where each carbon atom is at the junction of one five-membered and two six-membered rings. The first stage of successive hydrogenations of this type leads to C 76H 20 in which there are two C 10H 10 zig-zag strings, each string formed by the edge sharing of four C 6H 4 rings. The second stage of hydrogenation leads to C 76H 28 in which these strings are extended by the hydrogenation of pent–hex edges. The stereochemical pattern is determined by the instability of CH groups on the triple hexagonal junctions, the localisation of double bonds on pent–hex edges, and the formation of C 6H 6 rings.