Cyclic voltammetry of butyl iodides at an inert (glassy carbon) electrode allows the determination of an effective reduction potential for the tert- and sec-butyl radicals and of a lower limit of this quantity for the n-butyl radical. Taking into account the rapid self-reaction undergone by the radicals, a reduction potential (or, equivalently, the forward electron transfer rate constant) which is a combination of the standard potential and the intrinsic barrier of the R•/R- couple can be obtained. It provides all the necessary information for designing synthetic strategies based on the selective generation of either the radical or the carbanion from the electrochemical reduction of alkyl halides or of other radical-producing molecules. Modelling of the R•/R- kinetics by a quadratic activation-driving force relationship allows the determination of the intrinsic barriers and of the standard potentials. The latter were found to fall in the following ranges of values: t-Bu, 1.48, 1.60; sec-Bu, 1.38, 1.50; n-Bu, <≤-1.30, -1.42 V vs SCE. © 1989, American Chemical Society. All rights reserved.