The kinetics and products of reaction of a distorted bicyclic anilide (1, 2,3,4,5-tetrahydro-2-oxo-1,5-ethanobenzazepine) with 2-mercaptoacetic acid (2, thioglycolic acid) and ethyl 2-mercaptoacetate (3) have been studied in H2O at 25 degrees C. In both cases the products are the corresponding thio esters, For 2, the pH rate profile shows an apparent plateau from pH 2 to 9, followed by a linear decrease in rate with pH above the second pK(a) of thioglycolic acid (10.22). For 3, the pH rate profile shows a plateau at low pH with a domain of linear decrease in rate with pH above the pK(a) of 8. For 3 the reaction mechanism involves attack of the monoanion (3-S-) on the protonated amide (1-H+) throughout the entire pH region investigated. The same obtains for 2 below pH 3.5, with an additional efficient pathway involving the attack of 2-S- on neutral 1 at pH >3.5. In the latter case, in the neutral pH domain, the reaction of the thiolate of 2-S- with 1 is promoted by an intramolecular proton transfer from the pendant COOH which traps the unstable tetrahedral intermediate, thereby preventing reversal to starting materials. It is also observed that N-methylimidazole acts as a nucleophilic catalyst, reversibly reacting with 1 to form a transient N-acylimidazolium ion that is subsequently rapidly captured by both 3-S- and 2-S- to form their corresponding thio esters. The mechanism of these processes is discussed in the light of the attack of other bifunctional nucleophiles.