Regioselectivity in radical reactions of C-60 derivatives

Transient electronic spectra of mono-hydroxylated fullerene radicals, initi ally derived from water soluble malonic acid derivatives (C-60[C(COOH)(2)]( n), n=2-6) reacting with hydroxyl radical at a diffusion-controlled rate, s how a unimolecular growth in absorption on a timescale of 0.1-1 ms. It is s uggested 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 C-60[C(COOH)(2)](3)OH- anions d erived from two most abundant tris(malonate)s demonstrate a relation betwee n Coulson's free valence index for radical attack at a particular position and the stability of the corresponding product. They also suggest that afte r attack of the hydroxyl radical at the first encountered double bond, migr ation subsequently takes place to the position of highest free valence.