Under alkaline conditions, an amide group located as in 2-carbamoylphenyl mesitoate provides a highly effective means of overcoming the steric resistance to addition at the ester carbonyl group via intramolecular nucleophilic participation of the amide group acting through the amido-nitrogen. The corresponding intermediate imide is, however, much less reactive than the ester itself and its breakdown often represents the rate-determining step in the overall solvolysis. Introduction of N-methyl into the amide group results in a slightly reduced rate of rearrangement of ester to imide but considerably increased rate of imide solvolysis and hence a much greater overall rate for the ester solvolysis. The great difference in reactivity of the two imides is shown to support a mechanism for hydrolysis of the imides involving a general acid-catalysed attack of hydroxide ion in preference to the kinetically equivalent general base-catalysed attack of water. This result serves to underline the potential importance of undissociated hydroxy-groups (e.g., of serine and tyrosine) in the neighbourhood of the active sites of enzymes such as the esterases and peptidases.