A New Method of Determining the Relaxation Time and the Dipole Moment of Polar Substances; Its Application to Fatty Acids

A new method of determining the relaxation time and the electric dipole moment of polar substances has been worked out. This method uses dilute solutions of polar substances in non-polar solvents, and is based on measuring the dielectric constant and the coefficient of anomalous absorption of these solutions as a function of concentration. The measurements must be made at a constant frequency, in the vicinity of the maximum of anomalous absorption.

The method has been applied to formic, acetic, propionic, and $n$-butyric acids in the dioxane. The measurements have been made at 25.6-cm wave-length, using the Drude-Coolidge method, with Slatis' correction for induction effect in the condenser leads. The relaxation time data obtained were used to calculate the volume of the particle which becomes oriented by the impressed electric field. The volumes computed were proportional to the molecular volumes. This indicated that the anomalous absorption of ultra-high frequencies in fatty acids is due to the orientation of the entire molecule as a unit. This means that the dipole-bearing group of the fatty acid molecules (i.e., carboxyl) is not free to be oriented independently of the rest of the molecule. The experimental data used to calculate the relaxation time, were used to determine the dipole moments of fatty acids. The results obtained were in agreement with earlier determinations, thus furnishing a good support in favor of the validity of the relaxation time data obtained.