ELECTROSTATIC EFFECTS ON THE C-60 SURFACE OF ALKYL-C-60 RADICALS

The EPR spectra of alkyl- and fluoroalkyl-C-60 radicals are described and discussed. These radicals are of the general type XYZC-C-60, where X, Y and Z are CF3, F, H or CH3. It is shown that there is a competit ion among X, Y and Z for the pentagon position adjacent to the C-C-60 bond, and that in any given radical this position is gained by the mos t electronegative of them. Thus, if X, Y, Z is the order of decreasing electronegativity in the above sequence, X will occupy the pentagon p osition. If Y = X,the equilibrium conformation is asymmetric, with one X over the pentagon and the other over one of the hexagons. This conf ormation exchanges with its enantiomer above similar to 200 K. An expl anation based on quantum-chemical calculations of charge distribution on the C-60 surface indicates that the more electronegative ligands ar e attracted to regions of more positive charge over the pentagon.