Study of the conformational equilibrium between rotational isomers using ultrasonic relaxation and Raman spectroscopy. Part 3.—1-Bromo-2-cholroethane

Abstract

The rotational isomerism of 1-bromo-2-chloroethane has been studied by Raman and ultrasonic spectroscopy. Ultrasonic relaxation spectra have been measurd in the wide frequency range from 10 MHz to GHz, using the pulse, high-resolution Bragg reflection and Brillouin scattering methods. The enthalpy and volume differences between trans and gauche forms have been obtained from the temperature and pressure dependences of Raman bands, respectively. Combining the ultrasonic and Raman data, the entropy difference between two conformers has been estimated. The enthalpy difference of 1-bromo-2-chloroethane is almost the same as that of 1,2-dichloroethane, but the volume difference and entropy difference are small, in comparison with those of 1,2-dichloroethane and 1,2-dibromoethane. These results are interpreted in terms of the differences in the intermolecular interaction and packing state in the dihalogenoalkane molecules.