The conformational equilibrium as a result of the N-carbonyl bond rotation of several N-acyl- and N-alkoxycarbonyl-2-pyrrolines have been studied. The equilibrium constants and the rotational barriers were determined by theoretical methods (AM1, PM3, HF/3-21G( * ) and HF/6-31G*) and, experimentally, by dynamic NMR (coalescence temperature). The measured rotational barriers for enecarbamates were found to be similar to 16 kcal mol(-1) in C6D6 or C6D5NO2, whereas slightly higher values were found for enamides in C6D5NO2,. Contrary to enamides, the rotational barriers for enecarbamates were not affected by changes in the polarity of the solvent employed. (C) 2002 Elsevier Science B.V. All rights reserved.609416997381