Dielectric Properties of 2, 4-Pentanediol Diastereomers

Abstract

Little is known about the origin of the asymmetric distribution in the Davidson-Cole-type dielectric relaxations of polyhydroxy compounds such as diol and triol. The dielectric properties of the diastereomers of 2, 4-pentanediol were studied to clarify isomeric effects on the asymmetric distribution of relaxation times for liquid diols and triols.2, 4-Pentanediol was separated into the two isomers, racemic (syndiotactic) and meso (isotactic) molecules. The dielectric relaxation in the pure liquid state was measured with a transformer ratio-arm bridge in the frequency range from 23 Hz to 3 MHz. The static dielectric constants of racemic 2, 4pentanediol are equal to those of the meso diol, but they are smaller than those of nonfractionated 2, 4-pentanediol. The relaxation times decrease in the order of syndiotactic, non-fractionated, and isotactic 2, 4-pentanediol. The width of the distribution of relaxation times of non-fractionated 2, 4-pentanediol is not so different from those of the racemic and meso diols as expected from the effect of mixture. It was concluded that the origin of the distribution of relaxation times in polyhydroxy compounds could not be attributed merely to the coexistence of steric isomers in a liquid.