Theoretical study of proton transfer reactions in a gamma-lactam ring

A comprehensive study of the proton transfer reactions of the pyrazolidinon e ring in gas phase was carried out from nb initio calculations performed u sing a 6-31+G* basis set. All the structures studied were also optimized by using Moller-Plesset's perturbation theory. In the gas phase, the attack o f a hydroxyl group on a carbonyl compound may involve an interaction betwee n the hydroxyl ion and a proton, followed by proton transfer and formation of a water molecule. This reaction may interfere with the nucleophilic atta ck to the carbonyl group, which is related to the mechanism of enzymatic ac ylation in lactams. We identified three possible conformations for the tran sition state, and we studied the proton transfer reaction and the nucleophi lic attack for each structure.