ULTRASONIC RELAXATION AND VOLUME CHANGE DURING INTERNAL ROTATION IN 1,1,2-TRICHLOROETHANE

Ultrasonic absorption measurements have been carried out in solutions of 1,1,2-trichloroethane in various solvents. The observed relaxation has been attributed to the perturbation of the equilibrium between the trans and gauche rotational isomers. The concentration dependence of the relaxation parameters have served as an indirect check on the assumptions used in developing the ultrasonic theory. These results were used with those from a recent NMRstudy to calculate the volume change during isomerization, AF/F. This quantity had values in the range l%-3% showing that the assumption used in deriving the enthalpy difference ΔH from ultrasonic data (ΔV/V) (Cp/θ)δH is not justified. (Cp is the specific heat at constant pressure and 8 the coefficient of thermal expansion.) The temperature dependence of the relaxation time was found to be approximately the same as the pure liquid.