Dispersion and Absorption of Sound in Ethyl Formate and Study of the Rotational Isomers

Abstract

It was shown by Karpovich that there is the relaxational absorption of sound in liquid ethyl formate and that it results from the rotational isomerism about the C–O bond. Dispersion of sound velocity is expected from the absorption data, and its existence is confirmed by the present experiments. The sound velocities are measured over the frequency range from 300 kc to 9 mc/sec and at 5°C intervals from 10°C to 40°C by an ultrasonic interferometer. From these experimental results, the energy differences, the equilibrium constant, the rate of isomerization, and the height of the potential barrier hindering the internal rotation are calculated. The value of the energy difference is 2.50 kcal/mole and the height of the potential barrier, referred to the higher energy state is 3.38 kcal/mole. The calculated values of the heat capacity owing to the chemical reaction, the sound velocity at infinite frequency, and the maximum values of the absorption coefficient of sound per wavelength are in good coincidence with the experimental data.