Liquid Crystal Phases Exhibited by N,N′,N″-Trialkyl-1,3,5-Benzenetricaboxamides

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Abstract
When crystals of N,N′,N″-trialkyl-1,3,5-benzenetricarboxamides with alkyl groups from pentyl to octadecyl are heated, viscous birefringent fluids are produced at temperatures between 40 and 120[ddot]C depending upon the alkyl chain length and they are transformed into optically isotropic liquids above 200[ddot]C. Transition to a liquid crystal phase is accompained by an enthalpy change of 10 to 68 kJ mol−1 and that to an isotropic liquid by that of 6 to 22 kJ mol−1. The X-ray diffraction pattern of the unoriented liquid crystal resembles that known for smectic A or B phase. A layer thickness given by a sharp inner peak is 1.40 nm for the pentyl derivative and increases up to 2.26 nm for the octadecyl derivative. The second moment of the broad-line proton NMR spectrum shows an abrupt decrease at the melting point from several G2 to a few hundredths G2.

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