The Conformation of Aromatic Schiff Bases in Connection with Liquid Crystalline Properties

Aromatic Schiff bases of the type [graphic](R˭H) exist in a stable non-planar conformation in which the angle between the plane of the N-phenyl group and the rest of the molecule is 40–60°, the so-called acoplanarity.1 We suggest the molecule will become more rigid if an ortho methyl substituent (R=Ch3 is introduced. A number of p-n-alkoxy, p'-n-acyloxy- and p-n-alkoxy, p'-n-alkoxy-N-benzylidence-anilines, with or without an ortho methyl substituent have been synthesized. These compounds show nematic liquid crystallline behavior. The introduction of an ortho methyl substituents, gives a depression both of the melting and the transition point. Compared with the unsubstituted analogue the thermodynamic stability of the nematic phase is also lowered. p-(p-methoxybenzylidene) amino-m-cresol acetic, butyric, hexanoic and decanoic acid ester are monotropic liquid crystalline at room temperature.