The Aromatic Character of Reduced Fullerenes

The discovery of fullerenes offered a new challenge in the field of the study of the aromaticity of Ti-conjugated systems. These carbon allotropes embody completely conjugated spheroidal 7r-systems, so the carbon skeletons are boundaryless and thus large numbers of Kekule structures can be drawn. 

The aromaticity of fullerenes has been investigated theoretically and substantiated experimentally by NMR [154]. The best experimental method for studying the aromaticity of fullerenes was devised by Saunders and Cross, who encapsulated helium atoms inside fullerenes and measured their NMR spectra [155]. He NMR measurements show that C o exhibits the least aromatic character whereas C70 has the highest, and that the aromaticity of higher fullerenes lies between these two extremes. This is in contradiction to the initial suggestion in 1985 that C o is covered by a sea of n electrons that make it aromatic [14a, 156], and to the assumption of high aromaticity due to the large number of possible Kekule structures [157]. The reduction of fullerenes is not expected to modify their shape or symme- 

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