The Effect of 2- and 3-Lateral Substituents on the Acid Side of 4,4′-Disubstituted Phenylbenzoates and Phenylthiobenzoates on Mesomorphic Properties

A variety of esters/thioesters of the type where A or B=F, Cl, Me; Z=O, S and Y=C10, OC10, COC9, CO2C9 and OCOC9 for Z=O and C5, C10, OC7, OC10 for Z=S and R=C8H17, C10H2, C12H25 were synthesized and their mesomorphic properties determined by hot-stage polarizing microscopy. These properties were compared with those for the parent compounds having no lateral substituents. Melting temperatures decreased in most, but not all, of the esters but decreased in all the thioesters studied whereas clearing temperatures always decreased. The amount of temperature depression varied considerably for both transitions. Melting temperature depressions in the esters were similar for the 2- and 3-fluorine isomers but were larger in the 2- than the 3-isomers with larger lateral substituents. Clearing temperature depressions were usually more for the 2-F ester than for the 3-isomer but not always. This difference was less in the thioesters. Often clearing temperature depressions were greater than melting temperatur...