The water catalyzed hydrolyses of p-nitrotrifluoroacetanilide (3) and trifluoroacetanilide (8) were studied at various pH's and temperatures. The activation parameters for the water reactions of 3 and 8 are:  ΔH ⧧ = 14.4 ± 0.6 and 11.7 ± 0.3 kcal/mol and ΔS ⧧ = −36.1 ± 1.8 and −52.3 ± 0.7 cal/mol·K, respectively. These are consistent with reactions that involve considerable restriction of degrees of freedom of the solvent/substrate in the transition state. A proton inventory analysis of the rate constants for hydrolysis of 3 in media of different mole fraction D2O indicates the process involves two or more protons in flight or undergoing loosening of their bonding in the transition state. 18O-Labeled amides were subjected to the hydrolytic conditions for various times up to 3 half-times of hydrolysis and recovered. Mass analysis showed that the 18O content in the recovered amide did not change during the course of the reaction. All the data support a process where the rate-limiting step for the water reaction involves a concerted or nearly concerted formation of a diol which undergoes subsequent C−N cleavage in preference to OH expulsion.