Ultrasonic Relaxation and Axial—Equatorial Isomerization in Methylcyclohexane. II

Abstract

The ultrasonic absorption of pure liquid methylcyclohexane has been measured with a pulse technique over a frequency range of 0.6 to 10 Mc/sec from 60° to 120°C. These measurements together with those of the pure liquid previously recorded in the literature are consistent with a single relaxation process, the interchange of axial and equatorial isomers, with values of 2.9±0.5 kcal/mole and 3.2±0.6 cal/mole·°C for the difference in enthalpy and entropy, respectively, between axial and equatorial isomers, and 10.3±0.6 kcal/mole and 2.0±2.0 cal/mole·°C for the enthalpy and entropy of activation, respectively, for the conversion of axial into equatorial isomers. These results are in agreement with those derived from solution measurements with a streaming technique in Part I. They replace conflicting conclusions concerning the relaxation in methylcyclohexane recorded in the literature, which are shown to be without adequate foundation. The measurements are used to illustrate some common errors in the derivation of molecular parameters from ultrasonic measurement. The connection with conformational analysis and other physicochemical measurements is discussed.