X-Ray Diffraction Study of p-(Alkoxybenzylidene)-p′-Toluidines C5H11O-C6H4-CH=N-C6H4-CH3 and C8H17O-C6H4-CH=N-C6H4-CH3

The molecular and crystal structures of two p-(alkoxybenzylidene)-p'-toluidines C5H11O-C6H4- CH=N-C6H4-CH3 (1) and C8H17O-C6H4-CH=N-C6H4-CH3 (2), which form the nematic phase upon melting, is determined by X-ray diffraction. The geometry of the benzylideneaniline fragments in molecules 1 and 2 is actually identical. The crystal packings of I and 2 are characterized by the alternation of layers formed by loosely packed aliphatic fragments of molecules and layers of closely packed aromatic fragments. The packing in the aromatic regions of 1 follows the parquet pattern. The crystal packing of 2 has a stacking structure, which is formed by pi-stacking dimers superimposed on one another. The formation of the mesogenic phase upon melting of crystals 1 is due to the disturbance of the structurality of loose aliphatic layers with retention of the structure of the aromatic regions, which are stabilized by the cooperative effect of weak directed C-H center dot center dot center dot pi-system interactions. The mesogenic phase of crystals 2 is formed upon melting as a consequence of the retention of the structure of pi-stacking dimers.