Ab initio study of the vibrational spectrum and geometry of oxetane—I. Interpretation of the vibrational spectra

Abstract

As a first step toward the understanding of the role the zero-point energy of the fast vibrations plays in the effective puckering potential of oxetane, we have evaluated the force field of this molecule at three different values of the puckering angle by ab initio SCF calculations, using the 4–21 basis set. The force constants of the planar configuration, scaled by six empirical parameters, were used to establish the assignment ofthe high-frequency fundamental vibrations of oxetane and four of its deutero derivatives. Our results support most of the empirical assignments made by K ydd, W ieser and K iefer, but in each isotopomer one ofthe B 1 (out-of-plane) fundamentals must be assigned to a much higher frequency than they assumed. Except for a few cases where deviations up to 40 cm −1 occur, as a probable consequence of the inadequate description of ring strain and large anharmonicity connected with puckering, the theoretical spectrum reproduces most experimental frequencies to within 20 cm −1.