Design of novel mesomorphic compounds methyl-substituted N,N′-dialkanoyl-1,3-benzenediamines

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Abstract
Calorimetric, X-ray diffraction, and broad-line proton nuclear magnetic resonance studies on the thermal behaviour of N,N′-dialkanoyl-1,3-benzenediamines carrying one, two, three, and four methyl groups disclosed that the enthalpy change at the transition to an isotropic liquid can be considerably diminished by this substitution and that various mesomorphic states can be obtained by this approach. Thus, the 2-methyl compounds with decanoyl to octadecanoyl groups exhibit hexagonal disordered columnar phases. Furthermore, the enthalpy changes in the 2,4,6-trimethyl compounds with octanoyl to octadecanoyl groups are so much reduced that their mesophases are nematic in type. On the other hand, the viscous birefringent fluids formed by the 4-methyl, 2,4-dimethyl, 4,6-dimethyl, and 2,4,5,6-tetramethyl compounds give X-ray diffraction patterns indicating highly ordered structures.

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