Vibrational spectra and structure of small ring compounds—XXI 1,1,2,2-tetrafluorocyclobutane

Abstract

Abstract The infrared spectrum of gaseous and polycrystalline 1,1,2,2-tetrafluoro cyclo butane has been recorded from 33 to 4000 cm −1 and the Raman spectrum of the liquid sample has been measured from 70 to 4000 cm −1 . The vibrational data is consistent with a puckered molecule with C 2 symmetry. A vibrational assignment is proposed for the 30 fundamental modes based upon the observed band contours, relative band intensities, depolarization values and group frequency correlations. The band resulting from the ring-puckering mode was broad and centered near 90 cm −1 . Since no distinct Q -branches could be resolved, it was not possible to establish a unique potential function for this vibration; however, the data has been compared in a qualitative manner with cyclo butane and several of the substituted cyclo butanes. A correlation of this type implies that the barrier to planarity in tetrafluoro cyclo butane is 140 ± 50 cm −1 . The significance of this inversion barrier is demonstrated by a comparison of the established values for cyclo butane and 1,1-difluoro cyclo butane.