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A novel homologous series: 4-(4 -n-alkoxy benzoyloxy)-4 -methoxy benzyl benzoates is studied with a view to understanding the effect of a central group on the phenomenon of mesomorphism. The novel homologous series consists of eleven compounds. Mesomorphism commences from the second member of a series. All the mesogenic homologues from ethoxy to hexadecyloxy exhibit nematogenic mesomorphism without the exhibition of smectogenic character. The nematic-isotropic transition curve of the phase diagram behaves in normal manner up to the dodecyloxy homologue and then deviated for the tetradecyloxy and hexadecyloxy homologues. The solid-isotropic or nematic transition curve adopts a normal behavior in a zigzag manner. The nematic-isotropic transition curve shows an odd-even effect and continues up to the octyloxy homologue. Transition and melting temperatures including the textures of mesophases are determined by an optical polarizing microscope, equipped with a heating stage. The textures of the nematic mesophase are threaded or Schlieren in type. Analytical data and spectral data support the molecular structures. The mesomorphic behavior of the present series is compared with structurally similar other known series of differing central group (viz. N N and CO CH CH ) keeping rest of a molecular part unchanged. The nematic thermal stability of the series is 236.8 • C of a high melting type present series whose nematogenic mesophase length varies between 27 • C and 98 • C. Thus, series is only nematogenic without exhibition of a smectic mesophase.

ABSTRACT. Novel homologous series: RO-C 6 H 4 -CH=CH-COO-CH 2 -C 6 H 4 -Br (p) synthesized and studied with a view to understand and establish the effects of molecular structure on liquid crystal (LC) behavior of a series. Series consists of eleven homologues. C 1 to C 7 members of a novel series are non-liquid crystals. Mesomorphism commences from Octyloxy (C 8 ) homologue and continued upto hexadecyloxy homologue (C 16 ) as enantiotropic nematic without exhibition of smectic property. The textures of a nematic phase are threaded or Schlieren. Transition temperatures (table-3) and textures are determined by an optical polarizing microscopy equipped with a heating stage. Cr-N/I and N-I transition curve behaved in normal manner in phase diagram, showing their phase behavior (figure-2). Odd-even effect is absent for N-I transition curve. Analytical and spectral data confirmed the molecular structures of a series. The LC properties are compared with the structurally similar series. The transition temperatures are relatively lower than the corresponding n-alkoxy benzoic acid. Thus, present novel series is partly nematogenic with absence of smectic property whose mesogenic phase length is low and of low ordered melting type. Thermal stability for nematic is 93.0°C and the mesophaselength ranges from 8 to 21°C.

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