The pressure dependence of the static permittivity of pentanol isomers

It has been known for a long time that the measured values of the static permittivity of monohydric alcohols usually exceed values calculated from the Onsager equation1 using a magnitude of dipole moment estimated from dielectric measurements on the vapor or dilute solution. Such a departure may be explained by the existence of short range forces which may be taken into account by the g factor which appears in the expressions of Kirkwood2 and Frohlich. 3,4 Oster and Kirkwood, 5 using a model consisting of molecules linked into infinitely long chains by rigid hydrogen bonds with free rotation about the bonds, calculated g to be 2. 57. Values of g obtained experimentally from measured values of static permittivity tend to a limiting value at low temperatures and fall with increasing temperature. Typical examples for the alcohols6 considered in the present paper are shown in Figure 1. The variation of g with temperature has been explained by Dannhouser and Cole7 by assuming a distribution of lengths of hydrogen bonded chains. It is usually found that the low temperature value of g exceeds the Oster and Kirkwood value and this has been explained by Brot8 by assuming that hindered rotation about the hydrogen bonds favors a configuration leading to a high resultant dipole moment.