Mesomorphic Behavior of 2,4-Bis-(4-alkoxybenzylidene)cyclopentanones and Related Compounds

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Abstract
The mesomorphic properties of homologous series of 2,5-bis(4-alkoxybenzylidene)cyclopentanones, 2,6-bis(4-alkoxybenzylidene)cyclohexanones, and 2,7-bis(4-alkoxybenzylidene)cycloheptanoneshave been compared with each other. The clearing point is markedly depressed by increasing the size of the cycloalkanone ring. The cyclopentanone derivatives carrying the methoxy to pentyloxy groups are purely nematogenic, the next member exhibits a smectic A phase as well as a nematic phase. Smectic A and C phases are observed for the heptyloxy and octyloxy homologues, and only a smectic C phase for the later members. In both the cyclohexanone and cycloheptanone derivatives, the methoxy to decyloxy homologues exhibit a nematic phase and the higher members exhibit a smectic C phase. In addition, a smectic A phase appears in the nonyloxy and decyloxy homologues of the cyclohexanone series.

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