Reduction of phenacyl chloride in DM F containing 1% D2O is electrochemically irreversible, The observed products at the reduction potential are acetophenone plus dimeric product. Recovery of the ketone after short reaction times reveals the presence of considerable H/D exchange of the methylene hydrogens in competition with the reduction reaction. Similarly, in the reduction of 1, 2-diphenylpropanone, which proceeds with asymmetric induction, H/D exchange of the a hydrogen is very important. The exchange process appears to be part of the electrochemical reaction and is associated with the first electron transfer step. © 1977, American Chemical Society. All rights reserved.