The Mesomorphic Behavior of 5α-Cholestan-3β-yl ω-Phenylalkanoates

Abstract A homologous series of sixteen 5α-cholestan-3β-yl ω-phenylalkanoates was synthesized from 5α-cholestan-3β-ol and the imidazolides of the respective ω-phenylalkanoic acids. Microscopy and scanning calorimetry were used to identify the mesophases and to measure transition temperatures and associated latent heats. All homologs, except the phenylacetate, the 4-phenylbutyrate, and the 6-phenylhexanoate, are cholesteric and selectively reflect light. A smectic mesophase is observed only in the last five members. The values of the cholesteric-isotropic transition temperatures as well as the associated transition entropies fall on two distinct curves: an upper branch for odd acyl chain length and a lower branch for even acyl chain length. The smectic-cholesteric transition temperatures do not exhibit this odd-even effect but increase almost linearly with chain length.