Mesomorphic Properties of Some Ring-Methylated Phenyl Benzoyloxybenzoates

Abstract

To delineate the role of laterally placed methyl groups upon mesomorphic character, a series of esters of the general formula 1 was prepared, where R and S were ethoxyl and butyl, respectively, and A, B, Y, and Z were the nine independent combinations of methyl and hydrogen. Every derivative exhibited a nematic phase, and the nematic-isotropic transition temperatures decreased as the number of appended methyl groups increased. An investigation of the nematic-isotropic transition by means of differential scanning calorimetry revealed that méthylation of the central ring increased the intermolecular interactions and order in the nematic phase, relative to the isotropic phase, while no such effect was apparent upon méthylation of the terminal ring. This result demonstrates that the concept of increased intermolecular separation, resulting from laterally placed substituents, is not always sufficient to account for a decrease in nematic-isotropic transition temperatures. © 1972, American Chemical Society. All rights reserved.