Vibrational Spectra and Barriers to Internal Rotation in Some Halogen Substituted Ethanes

Abstract

The infrared spectra have been recorded from 33 to 4000 cm−1 for CH3CF2Br, CH3CBr2Cl, and CH3CBr3 and from 33 to 600 cm−1 for CH3CF2H and CH3CF2Cl for both the gaseous and solid states. The Raman spectra of CH3CF2Br and CH3CBr2Cl in the liquid state have also been recorded. The assignments of the 18 normal modes have been made on the basis of the band contours, Raman depolarization values, and characteristic ``group'' frequencies for the CH3CF2Br and CH3CBr2Cl molecules. The methyl torsional vibrations were observed for CH3CF2H, CH3CF2Cl, CH3CF2Br, CH3CBr2Cl, and CH3CBr3 at 248, 272, 275, 293, and 304 cm−1, respectively, in the solid state. From these assignments, barriers of 3.97, 4.80, 4.99, 5.66, and 6.08 kcal/mole were calculated, respectively. The effects of condensation on the torsional modes have been considered and the barrier values are compared with results obtained previously from similar molecules. Intermolecular fundamentals were observed for the CH3CF2H, CH3CF2Cl, and CH3CF2Br molecules in the far infrared spectra and possible assignments are discussed.