Mesomorphic behaviour of N, N-dialkanoyl-3,4,5,6-tetramethylbenzene-1,2-diamines and related compounds

DSC, X-ray, broad-line proton NMR, and microscopy studies on several series of N, N' -dialkanoylbenzene-1,2-diamines are presented. The melting point and associated enthalpy are not much affected by methylation of the aromatic nucleus. While the dimethyl compounds carrying heptanoyl-to-hexadecanoyl groups generate metastable mesophases below 111^oC, the 3,4,5,6- tetramethyl compounds carrying propionyl-to-hexadecanoyl groups produce stable hexagonal columnar mesophases appearing mostly above 200^oC. N, N'-dialkylbenzene-1,2-carboxamides are transformed into birefringent viscous fluids exhibiting a focal-conic texture at a temperature between 76 and 99^oC when the alkyl groups are decyl, undecyl, dodecyl, and tetradecyl.