The reaction of 15 aryl trifluoromethyl ketones with N-carbamoylmethyl-1,4-dihydronicotinamide was studied in aqueous sulfolane buffer. The unsubstituted ketone and those containing electron-withdrawing groups in the ring have the following reaction characteristics: a high yield of alcohol is obtained, the observed reaction rate is independent of ring substituent; however, when corrections are made for degree of hydration of the ketones the rate is correlated with Hammett .sigma. values with a rho of +1.98, a secondary isotope effect of .apprx. 1.08 and primary isotope effects of 1.45-1.62 are observed at 43.4.degree. C for the reaction of the dihydronicotinamide containing 1 or 2 atoms of deuterium at C-4, .**GRAPHIC**. = 15.2 kcal mol-1, and .**GRAPHIC**. = -27.0 cal deg-1 mol-1 for the unsubstituted compound, uncorrected for ketone hydration; .**GRAPHIC**. for reaction of the unhydrated ketone and dihydronicotinamide is estimated to be -45 to -50 cal deg-1 mol-1. The mechanism for the reduction is consistent with hydride transfer from reductant to oxidant, probably accompanied by blind-alley formation of an adduct between ketone hydrate and dihydronicotinamide. Ketones containing electron-donating groups in the ring react with the dihydronicotinamide in some undetermined way, giving little or no alcohol as product. [This reaction is important to the investigation of the reduction mechanism of carbonyl compounds by NADH and model compounds.].