الفهرس 
Effect of polarity and orientation of substituents on the mesophase behavior of some newly prepared bilaterally substituted liquid crystals
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Abstract
Eight homologous series of 2- (or 3-) substituted phenyl 4’-(4”-alkoxy (2”-, or 3”-substituted phenylazo) benzoates (InXY) were prepared in which the suffix 2X3 refers to the lateral substituent X attached to the terminal benzene ring that carries the alkoxy group, and the suffix 2Y3 refers to the substituent attached to the other terminal phenyl group. Within each homologous series, the length of the terminal alkoxy group varies between 8, 10, 12, and 16 carbons, while the lateral polar substituents, X and Y, alternatively varies between CH3 and F. Compounds prepared were characterized by infrared, 1H-NMR spectroscopy, mass spectroscopy and elemental analyses, and their mesophase behavior investigated by differential scanning calorimetry (DSC) and identified by polarized light microscopy (PLM). The results were discussed in terms of polarity and steric effects of the two lateral groups. Transition temperatures were first correlated with the alkoxy-chain length (n) within each homologous series. Comparative correlations were made to investigate the effect of the second lateral substituent on the mesophase behavior of the previously investigated mono- laterally substituted analogues. Studies were extended to compare the phase stability of each pair of compounds that maintain one of the substituents (X or Y) constant while the other changes.UV-vis spectroscopic study revealed that the compounds I8XY exhibited two absorption bands: low intense bands at 254-263 and a broad band at 364{u2013}376. These bands are attributed to the s{u2013}s{u2217} transition of the phenyl rings and the whole mesogenic portion