Structures of C70X42 and C70X44, X=H, F

Abstract

The structures and stabilities of C70X42 and C70X44 where X is H or F, have been investigated using the AM1 Hamiltonian and the program mopac 6.0. As in C70X36, C70X38 and C70X40, structures are based on an equatorial plane of ten bare carbon atoms separating two C30 hemispheres which do not interact strongly with each other. In C70X42 there is a C30X20 hemisphere and a C30X22 hemisphere whereas in C70X44 there are two C30X22 hemispheres. Within each hemisphere, the bare carbon atoms are grouped as isolated C6 rings or as isolated CC units. The C30X20 hemisphere was the same as in C70X38 and C70X40. All 126 possible C30X22 hemispheres were considered. Each of these hemispheres has five rotation positions relative to the other hemisphere, and the 106, which do not have a mirror plane exist as a pair of optical enantiomers. The most stable isomers for C70F42 and C70F44 contain two unfluorinated C6 rings as was also found for C70F40. In contrast to C70F38, C70F40 and C70F42, there is one isomer of C70F44 which may be significantly more stable than all other isomers. The most stable isomers of C70H42 and C70H44 are different to the fluorides and there are many isomers of the hydrides of comparable stability with zero, one or two unhydrogenated C6 rings.