Intramolecular Electron Transfer and Dehalogenation of Anion Radicals. 3. Halobenzonitriles and Cyanobenzyl Halides

One-electron reduction of halobenzonitriles and cyanobenzyl halides produces the anion radicals which then undergo intramolecular electron transfer leading to dehalogenation. Kinetic spectrophotometric pulse radiolysis allowed the observation of the halobenzonitrile anion radicals and the determination of their dehalogenation rates. The rates varied from 10⁴ to >10⁷ s^-1 depending on the halogen and its position relative to the cyano group. The production of X^- was measured in steady-state radiolysis experiments, and the participation of cyanophenyl radicals as intermediates was also deduced from observation of chain reactions. The anion radicals of cyanobenzyl halides were not observed since they dehalogenate very rapidly. The cyanobenzyl radicals produced by this process were monitored spectrophotometrically. The rates of dehalogenation of the anion radicals studied here are at least 5 orders of magnitude higher than the corresponding values determined previously for analogous nitro derivatives, but the pattern of reactivities is similar in both series of radicals.