Regioselectivity in radical reactions of C60 derivatives

Abstract

Transient electronic spectra of mono-hydroxylated fullerene radicals, initially derived from water soluble malonic acid derivatives (C60[C(COOH)2]n, n = 2–6) reacting with hydroxyl radical at a diffusion-controlled rate, show a unimolecular growth in absorption on a timescale of 0.1–1 ms. It is suggested that the reason for this slower growth is migration of the hydroxy group to a more stable position. Semi-empirical molecular orbital (AM1 and PM3) calculations on the symmetry-distinct C60[C(COOH)2]3OH− anions derived from two most abundant tris(malonate)s demonstrate a relation between Coulson’s free valence index for radical attack at a particular position and the stability of the corresponding product. They also suggest that after attack of the hydroxyl radical at the first encountered double bond, migration subsequently takes place to the position of highest free valence.