Interpretation of the vibrational spectra of small ring systems: I. 1,1,2,2-Tetrachlorotetrafluorocyclobutane and 1-chloro-2,2,3,3-tetrafluorocyclobutane

Abstract

The infrared spectra of the vapor and crystalline states of cyclo-C 4Cl 4F 4 and cyclo-C 4ClF 4H 3 have been measured between 200 and 4000 cm −1. The low temperature infrared spectrum of each molecule has also been studied down to 33 cm −1. A weak band at 102 cm −1 in the infrared spectrum of polycrystalline c-C 4ClF 4H 3 has been assigned to the ring-puckering fundamental; however, the corresponding vibration for c-C 4Cl 4F 4 was not observed. The Raman spectra of each compound have been recorded at ambient and liquid nitrogen temperatures to within 50 cm −1 of the exciting line. Although it has not been possible to establish the equilibrium structure of the c-C 4ClF 4H 3 skeleton from the infrared and Raman data, the spectra of c-C 4Cl 4F 4 are explained in terms of C 2v molecular symmetry. A vibrational assignment is suggested for each molecule on the basis of relative band intensities, group frequency correlations and depolarization ratios.