Ultrasonic investigation of the viscosity dependence of the rate constants of rotational isomerism of dibromoethane and dibromopropane in solution

Abstract

Ultrasonic relaxation spectra due to the rotational isomerism of 1,2-dibromoethane and 1,2-dibromopropane in n-hexane and diisobutyl phthalate have been measured as a function of solution viscosity. The rate constant of the rotational isomerism was determined by analysis of the frequency dependence of the ultrasonic absorption or sound velocity. The reaction rate constants of the rotational isomerism increased with decreasing solution viscosity. The viscosity dependence of the rate constant for 1,2-dibromoethane solutions is well interpreted in terms of Kramers' model. For 1,2-dibromopropane, the pre-exponential factors predicted by Kramers' model are in agreement with experimental results in the low-viscosity region, while in the high-viscosity region deviation from Kramers' theory was found in the pre-exponential factor. The deviation is considered to be due to the strong interaction between 1,2-dibromopropane and diisobutyl phthalate.