THE INFLUENCE OF LATERAL FLUORO-SUBSTITUENTS ON TGB PHASES IN CHIRAL PROPIOLATES

The transition temperatures and associated enthalpies of chiral and ra cemic 1-methylheptyl 4'-[(2- or alkoxyphenyl)propioloyloxy]biphenyl-4- carboxylates are reported along with phase diagrams for binary mixture s of (R)- and (S)-isomers. The position of the fluoro substituent was found to influence the formation of twist grain boundary phases both i n the enantiomers and in binary mixtures of enantiomers. DSC studies r evealed that the enantiomeric 3-fluoro compounds possessed a diffuse l iquid-liquid transition above the clearing point, which did not arise for the racemates or for the 2-fluoro Circular dichroism and optical r otation studies carried out over the temperature range of the diffuse liquid phase, confirm that a form of cybotactic, chiral organisation i n the isotropic liquid is responsible for this phenomenon.