The single crystal x-ray structure of C70Me8;: The origin of the fullerene addition patterns for bulky groups

The first complete proof of the equatorial addition pattern in [70]fullerene is provided by a single crystal x-ray structure of C70Me8. Compared to the bonds in the parent fullerene, those having a methyl group attached are lengthened, those having two methyl groups adjacent at each end are shortened due to compression by these groups, and some hexagonal rings show greater delocalisation (more aromaticity) than the corresponding rings in the precursor fullerene. In contrast to the 1,2-addition of sterically undemanding groups, bulky groups generally undergo 1,4-addition, but only give 1,2-addition if there is a need to quench an intermediate radical. The manner in which this gives. rise to the patterns seen in C60X6, C60X8 and C70X10, where X is bulky, is proposed.