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This paper examines in some detail the e ect of introducing the oxadiazole fragment into the molecular core of liquid crystals on their physico-chemical properties. The results of this study are compared with those obtained for other molecular fragments, and are rationalized in terms of existing theories.

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In the last years bent banana-shaped mesomorphic molecules found an increasingly great interest among theoreticians and experimentalists due to the nature of this type of liquid crystals to exhibit a spontaneous polarization in the absence of any chiral group in the molecules. Similar property was found in mesomorphic 1,3,4-oxadiazoles containing as a central unit the five-membered heterocycle with the symmetric positions of heteroatoms and as the link units -the ester groups [I].In the present work 1,2,4-oxadiazoles -asymmetric isomers of the liquid crystals mentioned above, keeping the same banana-shape, were synthesized and their properties were investigated.

New liquid crystalline oxadiazoles containing terminal CI-group and phenylcyclohexane fragment together with their biphenyl analogues have been synthesized and investigated by DSC and polarizing microscopy. There is a direct dependence of results obtained on the central heterocyclic structure and the character and position of the substituent related to the asymmetrical heterocyclic unit.

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