Structure and ring inversion of 2-pyrrolidone. Semiempirical quantum chemical study and analysis of X-ray data

Abstract

The equilibrium structure and the ring inversion potential of the 2-pyrrolidone molecule has been studied by the semiempirical CNDO/2 and INDO methods. The calculated geometrical parameters are compared with experimental X-ray data with earlier Consistent Force Field (CFF) results. The ring inversion is analyzed in terms of two types of puckering coordinates. The CNDO/2 method was found to yield a strongly nonplanar 2-pyrrolidone ring due to the overestimation of the amide pyramidality while INDO calculations led to a slightly nonplanar ring with an extremely low barrier of inversion.