The cleavage of radical anions of substituted α-phenoxyacetophenones, X-C₆H₄COCH₂OPh, IIa-k, has been studied in DMF by voltammetric and coulometric techniques. The standard potentials (E°) for formation of and rate constants, k, for the cleavage of the radical anions were determined using linear sweep voltammetry, LSV, together with digital simulation and previously reported laser flash photolysis data. The rate constants cover a range of almost eight orders of magnitude (0.4 s^-1 for X = p-MeCO- to 1.3·10⁷ s^-1 for X = p-MeO-). The relative driving forces, ΔΔG°(het)(RX^.-), for the heterolytic cleavage of the radical anions (to give R^. + X^-) were estimated from thermochemical cycles. A combined plot of log(k) versus ΔΔG°(het)(RX^.-) for the radical anions of IIa-k and of α-aryloxyacetophenones gave a curve with α = 0.5 at high driving forces and α = 1 at low driving forces, where α = δΔG₀(paragraph)/δΔG°. The plot was analyzed using a model in which reversible cleavage of the radical anions takes place inside the solvent cage followed by (counter)diffusion of the fragments out of the solvent cage. The change in the value of α is interpreted as a change in the rate limiting process from chemical activation (i.e., fragmentation) to counterdiffusion. The model allowed the determination of the absolute values of ΔG°(het)(RX^.-) and the intrinsic barrier, ΔG₀(paragraph), for the fragmentation of the radical anions (8 ± 1 kcal mol^-1, 0.35 eV). This leads to an estimate of the homolytic bond dissociation free energy of the C-OPh bond in the unsubstituted α-phenoxyacetophenone.