Mesomorphic behaviour of four series of compounds derived from N,N'-dialkanoylbenzene-1,3-diamine

Syntheses, differential scanning calorimetric (DSC) and X-ray diffraction (XRD) studies were carried out on the following four series of compounds: the 5-methyl-2-alkanoyloxy, 4,5-dimethyl-2-alkanoyloxy, 2-methyl-5-tert-butyl-4-methoxy and 2,5,6-trimethyl-4-hydroxy derivatives of N,N'-dialkanoylbenzene-1,3-diamine. The high-temperature phases given by the first and second series are viscous fluids. On supercooling of the isotropic liquid, a hexagonal ordered columnar phase appears, as demonstrated by the XRD pattern. This behaviour is in sharp contrast to that of the 2,5-dimethyl-4-alkanoyloxy derivatives, which are isomeric with compounds of the second series and nematogenic, Many homologous members in the third and fourth series exhibit a nematic phase. The methoxy group introduced to the 4-position of the 2-methyl-5-tert-butyl derivative leads to a significant depression of the clearing point relative to the parent compound.