Aryl cyclopropyl ketones have frequently been used as probes for single-electron transfer in organic reactions. The implicit assumption in these studies is that upon one-electron reduction, the corresponding arylcyclopropylketyl anions will undergo ring opening in analogy to the cyclopropylcarbinyl free radical. Earlier work in our laboratory has shown that ring opening of arylcyclopropylketyl anions is kinetically and thermodynamically unfavorable when the only substituents on the cyclopropane ring are alkyl or H. This sluggishness is attributable to a loss of resonance energy upon ring opening which is not fully compensated by the relief of cyclopropane ring strain. Consequently, aryl cyclopropyl ketones are unsuitable probes for single-electron transfer. In this paper, we examine the effect of radical-stabilizing substituents (phenyl and vinyl) on the ring opening of arylcyclopropylketyl anions. We have studied the mechanism, kinetics, and products of decay of radical anions generated electrochemically from trans-1-benzoyl-2-phenylcyclopropane and 1-benzoyl-2-vinylcyclopropane. The radical anions generated from these precursors each undergo ring opening(k approximate to 10(6-7) s(-1)) which is estimated to be exothermic by ca. 2 kcal/mol.