Single electron-transfer as rate-determining step in an aliphatic nucleophilic substitution

The rate of the reaction between the anion of 1,4-dihydro-4-methoxycarbonyl-1-methylpyridine (1^- and sterically hindered alkyl halides, and between the perylene dianion (Pe^2-) and t-butyl chloride and sec-butyl bromide has been measured by electrochemical techniques. The rate was found to be close to the rate of single electron-transfer (SET) from anion radicals (A{minus sign, dot below}) with the same standard potential as 1^•/1^-, resp. Pe^{{minus sign, dot below}}/Pe^2- to the corresponding alkyl halides. The kinetic results strongly suggest that a SET mechanism is the rate-determining step in these nucleophilic substitutions.