Electrostatic effects on the C60 surface of alkyl-C60 radicals

Abstract

The EPR spectra of alkyl- and fluoroalkyl-C₆₀ radicals are described and discussed. These radicals are of the general type XYZC-C₆₀, where X, Y and Z are CF₃, F, H or CH₃. It is shown that there is a competition among X, Y and Z for the pentagon position adjacent to the C–C₆₀ bond, and that in any given radical this position is gained by the most electronegative of them. Thus, if X, Y, Z is the order of decreasing electronegativity in the above sequence, X will occupy the pentagon position. If Y = X, the equilibrium conformation is asymmetric, with one X over the pentagon and the other over one of the hexagons. This conformation exchanges with its enantiomer above ∼ 200 K. An explanation based on quantum-chemical calculations of charge distribution on the C₆₀ surface indicates that the more electronegative ligands are attracted to regions of more positive charge over the pentagon.