Study of the conformational equilibria between rotational isomers using ultrasonic relaxation and Raman spectroscopy. Part 2.—Di- and tri-halogenoalkanes

Abstract

The conformational changes between rotational isomers of 1,2-dichloropropane, 1,2-dibromopropane, 1,1,2-trichloroethane and 1,1,2-tribromoethane have been investigated by ultrasonic relaxation and Raman spectroscopy. All thermodynamic parameters, ΔH, ΔV, ΔS, ΔH^≠ and ΔS^≠, in the energy diagram and the kinetic parameters, k_f and k_b for the rotational isomerism have been completely determined, using ultrasonic relaxation parameters and the data for the temperature- and pressure-dependence of the Raman spectra. Significant differences have been observed in the thermodynamic parameters for chloro- and bromoderivatives and these can be ascribed to the intermolecular interactions in the liquid. In addition, it is suggested that a strong correlation exists between the relaxation frequency and the molecular weight.