The Effect of Carbonyl Containing Substituents in the Terminal Chains on Mesomorphic Properties in Some Aromatic Esters and Thioesters. 3. Acyloxy Groups on the Acid End

A select number of 4-alkyl and alkoxyphenyl-4′-acyloxybenzoates and phenylthio-benzoates of the type where X = RCO2, Y = R′ or OR′, and Z = O or S have been prepared and their mesomorphic properties determined by hot-stage polarizing microscopy. These were compared with the properties for the corresponding alkoxy esters/thioesters (X = RO). Replacement of the acid RO with RCO2 favors the nematic phase in all series and the smectic C phase in the esters. This latter phase is slightly less favored in the thioesters. Smectic A phases were definitely less favored occurring only in the esters with Y = R'. Smectic B phases were also observed; most were monotropic. All seemed to be crystalline smectic B phases. A comparison of the mesomorphic properties of the esters with X = RCO2 with those when Y = OCOR’ showed only small differences in these two isomeric series. The types of mesophases which were enhanced were the same in both series. Monotropic smectic B phases seemed more prevalent when Y = OCOR’ than when X = RCO2, possibly due to lower crystallization temperatures. Melting and clearing temperatures did not vary appreciably in these two series nor from those observed when X and Y are alkyl or alkoxy groups.