Kinetic Electron Spin Resonance Spectroscopy Part 61.—Formation and Termination Reactions of Aliphatic Radicals by Reductive Dissociation of Halogeno-compounds

Abstract

The reactions of hydroxy-alkyl radicals with a variety of aliphatic halogeno-compounds RX have been studied. By examining the effects of varying concentrations of RX on the concentration and lifetime of the hydroxy-alkyl radicals it is shown that these are replaced by radicals R· produced by electron transfer to RX and subsequent loss of X–.

Peak intensity anomalies are satisfactorily explained in terms of a hyperfine energy induced E–A polarization plus a contribution from an initial (emissive) polarization.

Self-termination rate constants for nine aliphatic radicals have been determined. These rate constants are in the range 3 × 108 to 5 × 109 dm3 mol–1 s–1 in propan-2-ol at 300 K and have an inverse correlation with molecular mass.

The problems associated with measurements of rate constants for the electron transfer step are discussed. For the reaction of Me2ĊOH with trichloroacetic acid the value (6.1 ± 1.9)× 106 dm3 mol–1 s–1 was obtained in propan-2-ol at 293 K.