Molecular determinants for drug-receptors: Part 11. The preferred conformation of N-( p-anisoyl)pyrrolidin-2-one (“Aniracetam”) in the solid and solution states as indicated by X-ray crystal structure analysis, dipole moment and theoretical calculations

Abstract

N-( p-anisoyl)pyrrolidin-2-one in the crystalline state exhibites a cis— rans conrotatory conformation with NCO and COC ar rotational angles of 33.5° and 38.5° respectively, and the p-methoxy group situated cis to the central carbonyl bond, as shown by X-ray structure analysis. As suggested by dipole moment analysis and MMP2 molecular mechanics calculations, in solution similar conrotatory models hold for both c- and t-subconformers having the p-methoxy group cis or trans to the central carbonyl bond. INDO calculations were also carried out, indicating that both subconformers are equally stable.