CHARGE DELOCALIZATION IN HYDROFULLERENES AND SUBSTITUTED HYDROFULLERENES - EFFECT OF DEPROTONATION

The delocalisation that occurs upon deprotonation of a series of hydro fullerenes and substituted hydrofullerenes is analysed, The charges an d bond lengths of the acidic and basic forms of each system are consid ered, We find approximately one electron delocalising from the deproto nated C atom to the rest of the system on deprotonation, The softness of the cage and the bond alternation permit delocalisation of the resu lting negative charge over the main part of the fullerene cage, follow ing the pattern of conjugated bonds, showing a clear 'delocalisation p ath', The same paths were found for hydrofullerenes and substituted hy drofullerenes, so that the properties of different functional groups a re seen not to influence the delocalisation pattern in a significant w ay, This delocalisation greatly stabilises the basic form and explains the high acidities of these hydrocarbon systems, The deprotonation en ergies for the two most stable C60H2 and the two most stable C70H2 iso mers have been calculated at the ab initio HF/6-31G level of theory, 5,6-C70H2 was found to be more acidic than 1,2-C60H2. This inversion a s compared to H-1 NMR predictions results from the difference in cage structure of C-60 and C-70, The delocalising charge reaches the equato rial band of six rings present in the C-70 structure, giving rise to a better stabilisation of the basic form than for 1,2-C70H2.