Effect of Chain Length on Mesomorphism of Steroid Esters of 4-(4-Alkylphenyl-X)benzoic Acids with X = CO, O, S, and CH2

Article abstract of DOI:10.1021/j100246a037

To examine the effect of bent shapes on mesomorphic properties a homologous series of steroid esters have been prepared: H(CH2)n-4-C6H4-X-4-C6H4COOR, X = CO, O, S, CH2, R = cholesteryl, β-sitosteryl, cholestanyl, stigmasteryl, ergosteryl; n = 0-15.The chain elongation results in an increase in not only the molecular length but also the breadth due to the angular linkage, X.The steroid portions are of primary importance for the mesomorphic properties of the present series, and the thermal stability of the mesophases is strongly dependent on the mesogenic power of the aryl portions, where the effective order is CO > O > S > CH2.The transition enthalpies and entropies for the smectic A-cholesteric and cholesteric-isotropic (Ch-I) transitions are almost independent of the chain length of the alkyl group, indicating that a long alkyl chain has no role from a thermodynamical piont of view.Within the mesophases, the aryl and steroid cores are assumed to be piled up, interacting with each other, and the alkyl groups are apart from each other to avoid short-range interaction.