Synthesis and Liquid Crystal Properties of Some Urethans

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Abstract
The urethan (carbamate) linkage (-NHCOO-) has been investigated as a central group in liquid crystal systems. Cholesteryl N-para-substituted-phenylcarbamates exhibit cholesteric mesophases with mesophase stability roughly parallel to increasing molecular polarizability. A smectic, in addition to a cholesteric mesophase was found in the case of cholesteryl N-n-hexadecylcarbamate. The n-octyl analog has a monotropic cholesteric mesophase, while the n-butyl analog is not mesogenic. The N-para-methoxyphenylcarbamates of cholesterol, cholestanol, stigmasterol, α-sitosterol, campesterol, and 5-androstene-3β-0l-17-one, with the exception of the latter which was not mesogenic, exhibit enantiotropic mesophases. Twentyfive other non-steroidal urethans having a wide variety of structures, as well as several urea derivatives, were prepared but none was mesogenic.