Ab Initio Studies on Amides: Pyrrolidin-2-one (γ-Butyrolactam)

Abstract

By optimization with the 3-21G basis set, pyrrolidin-2-one is found clearly to prefer an envelope conformation with the flap bent 27.4° out of the NC(=O)C reference plane. The ring may be bent or twisted through a few degrees at low energy-cost, and undergoes rapid inversion through a planar-ring structure lying only 3.3 kJ mol^-1 above the preferred equilibrium structure.