Synthesis and Mesomorphic Properties of the Homologous Series of 4-Alkyl or Alkoxy-4?-Bromo or Cyanotolanes

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Abstract
A homologous series of 4-alkyl or alkoxy-4′-bromo or cyanotolanes in which the alkyl group is C4 → C10 and the alkoxy group is C1 → C12, has been prepared. Interphase transitions between solid, mesomorphic and isotropic phases were studied by hot stage microscopy and differential scanning calorimeter. The bromo compounds have a smectic polymorphism. Three pure products of cyano derivatives with the chains C9H19O, C10H21O and C10H21 present an enantiotropic or monotropic reentrant nematic phase at atmospheric pressure. The reentrant phenomenon itself will be discussed as well as the absence of correlation between TNA/TNI McMillan parameter and the heat of transition. A plot of the nematic isotropic transition temperatures against the number of carbon atoms in the alkoxy chain shows the usual odd even effect.