Ultrasonic studies of rotational isomerism in various methylpentanes

Abstract

Ultrasonic attenuation and velocity have been measured in 2-methylpentane, 3-methylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,2,4-trimethylpentane and 2,3,4-trimethylpentane from 233 to 293 K. The contribution to the attenuation from shear processes has been estimated from viscosity measurements and the corrected data have been analysed in terms of rotational isomerism. The conformational energetics so obtained are compared with those predicted on the basis of non-bonded van der Waals' interactions between neighbouring groups. In general, there is agreement between the theoretical and experimental energy differences between stable rotational states, but observed activation energies for rotation are less than those predicted theoretically.