Synthesis, physical and mesomorphic properties of Schiff's base esters containing ortho‐, meta‐ and para‐substituents in benzylidene‐4′‐alkanoyloxyanilines

Abstract

Three series of Schiff's base esters, 2‐hydroxy‐4‐methoxybenzylidene‐4′‐alkanoyloxyaniline, 2‐hydroxy‐3‐methoxybenzylidene‐4′‐alkanoyloxyaniline and 3‐methoxy‐4‐alkanoyloxybenzylidene‐4′‐alkanoyloxyaniline, which possess mono‐ and di‐substituted moieties at both ends of the molecules have been synthesized and their mesomorphic properties investigated along with physical characterization (elemental analysis, mass spectrometry, Fourier transform IR and high resolution NMR). The effect of lateral methoxy and polar hydroxy groups on the mesomorphism of the title compounds was studied, based on the thermal properties and textural analysis. The results indicate that compounds with the larger number of carbons in the alkyl chain prefer smectic phase formation and possess higher transition temperatures and molecular polarizability along the long axis. Further analysis shows that the greater shielding effect (through the formation of intramolecular interaction) leads to lower molecular broadening and results in higher clearing points. Increase in melting point due to the lengthening of the alkyl chain is associated with the increase in van der Waals attraction between the molecules. These compounds exhibit nematic, smectic (SmA and SmC) phases depending on the type and position of the substituents.