Analysis of the asymmetric ring puckering potential in 1-oxo-1-chloro- phosphetane and of theoretical vibrational spectra

The asymmetric ring puckering potential in 1-oxo-1-chloro-phosphetane (c-C₃H₆POCI) was calculated using the 6-311+ G** basis set and the MP2 as well as the DFT method and fitted as function of the ring puckering coordinate x. It turned out that on MP2 level the potential is clearly of a double well type with an equatorial and an (higher in energy) axial minimum, while on DFT level no axial minimum exists, just a shoulder in the potential function. Based on our, yet unpublished results on thietane dioxide we conclude that the DFT curve should be the more reliable one. Since we expect that barriers in DFT are somewhat too low. experimentally an axial conformer might still exist, hut with an extremely low barrier to ring puckering. Thus with our DFT calculations we predict the vibrational infrared and Raman spectra of the equatorial conformer only, since even if an axial one would exist experimentally its energy would he much higher than that of the equatorial one and thus its contribution to the conformational equilibrium would he negligible Thus we consider our prediction based on DFT calculations as very reliable. The distributions of the potential energies of the different normal modes among the symmetry coordinates (PED) were calculated and used to assign the lines in the spectra to the different motions of atoms.