Mesomorphic Behaviour of Some Esters : Ethyl p-(p'-n-Alkoxycinnamoyloxy )Benzoates

Applied Chemistry Department, Faculty of Technology & Engineering, M. B. University of Baroda, Baroda-350 001, India
Manuscript received 4 February 1980, accepted 9 July 1980

A new homologous series of mesogenic esters— ethyl \(p\)-(\(p\)'-\(n\)-alkoxycinnamoyloxy)- benzoates has been synthesized by treating trans-\(p\)-\(n\)-alkoxycinnamoyl chlorides with ethyl \(p\)-hydroxybenzoate and the phase transitions of the various ester mesogens have been determined. Monotropic nematic mesophase is exhibited alternately by the odd members up to the third derivative while the second member exhibits enantiotropic nematic mesophase. The second and third members show smectic mesophase in mono-tropic conditions. From the fourth member onwards enantiotropic mesomorphism is exhibited. Polyniesomorphism begins from the second member though in the monotropic conditions. The nematic-isotropic (even) and smectic-isotropic transition turves, taken in continuation, show a gradual fall followed by a plateau and ending with another smooth fall ; the smectic-nematic transition curve shows a steep rise upto the hexyl member. From heptyl to octadecyl derivatives, only smectic mesophase is exhibited with definite transitions to isotropic liquid. While all the nematic phases are with threaded texture, the smectic mesophase shows focal conic Grandjean plates with fan shape texture. The usual odd- even effect is observed not only with regard to nematic mesophase but also the smectic mesophase which is a rare behaviour. Similarities and contrasts with other homologous series yield interesting features. The thermal stabilities are comparable and the mesomorphic range as obtained is quite true to the molecular characteristics. This homologous series of mesogens can be considered to be one of medium melting type though some characteristics of the high melting series are clearly exhibited. In all twelve new mesogens have been investigated for their characteristic behaviour.