UNIMOLECULAR DISSOCIATION OF BENZYL HALIDE RADICAL-ANIONS STUDIED BY LOW-TEMPERATURE PULSE-RADIOLYSIS

The one-electron reduction of benzyl halides (BzX; X=F, Cl, Br) by solvated electrons in 2-methyltetrahydrofuran has been investigated by using a pulse radiolysis technique at different temperatures above 77 K. The radical anions of BzX (lambda(max)=300 nm) formed by the capture of an electron in the pi*-orbital of the benzene ring dissociate into Bz. (lambda(max)=320 nm) and X- via Bz./X- complexes (lambda(max)=340 nm for BzCl and 370 nm for BzBr). The corresponding species were observed with 4-phenylbenzyl halide at 85 K and below. A spectral change observed at 95 K has been attributed to a structural change of the biphenylyl group. The dissociation rate of the radical anions increased in the order BzF<BzCl<BzBr. On the basis of these results, the reaction mechanism is discussed.