Mesomorphic Properties of Some α-Methyl Cinnamic Acids and their Esters

Two homologous series of liquid crystalline substances have been synthesized and their mesomorphic properties studied. These are (i) trans-p-n-alkoxy-α-methyl cinnamic acids and (ii) trans-p-n-alkoxy-α-methyl-p'-cyanophenyl cinnamates. The esters are colourless and fairly low melting materials of high positive dielectric anisotropy. The effect of the α-methyl group on the mesomorphic thermal stability of both the homologous series is discussed and compared with other materials of similar structure. The nematic-isotropic transition temperatures in ascending series of the esters show an initial decrease and then a gradual increase, which is not a commonly observed phenomenon for homologous series of liquid crystalline substances.