AbstractConsistent force‐field calculations were performed on a series of methyl substituted pyrrolidones. Methyl substitution enhances the non‐planarity of the pyrrolidone ring in a way wich varies with the position of the substituent. The effect of ring distortion is to produce skeletal contributions to the rotatory strength of thenπ* transition of the amide group. Depending on position of substitution, these reinforce or oppose the substituent contribution to optical activity. There is favorable agreement between the conformational calculations and the quadrant rule for the optical activity of thenπ* transition of the peptide chromo