The cyclic voltammetric investigation of a series of α-substituted acetophenones allowed the identification of the concerted and stepwise character of the dissociative electron transfer reaction, and, in the stepwise cases, the determination of the cleavage rate constants and the standard potentials for the formation of the anion radical. Analysis of the data, using thermodynamical parameters derived from experiment and from literature points to three mechanism governing factors, the oxidability of the leaving group, the bond dissociation energy of the bond being broken, and the LUMO energy. The first of these factors appears to be largely predominant in many cases in the control of the concerted vs stepwise dichotomy. The fluoro substituent provides a reverse example where the bond strength overcomes the unfavorable effect of the leaving group oxidability. It is also an exception, in terms of anion radical cleavage reactivity, where the strength of the C−F bond significantly contributes to slow down the cleavage as opposed to the other substituents where solvent reorganization appears as largely predominant. In the concerted cases, the estimated lifetime of the anion radical is clearly larger than the time of a vibration. The concerted character of the reaction thus results from an energetic advantage rather than from the “nonexistence” of the anion radical intermediate.

Mechanism of the oxidative dimerization of DTF (dithiafulvenes) to form TTF vinylogues (tetrathiafulvalenes) has been investigated by cyclic voltammetry at low and high scan rates for a series of substituted DTF. It involves first the formation of the cation radical which couples to form the protonated dication. This dication slowly deprotonates to give the final TTF (k ) 0.5-1 s -1 ). The dimerization rate constant was found to be in the range of k dim ) (2-4) × 10 8 L mol -1 s -1 and not vary much with the nature of the substituent.