Synthesis and Liquid Crystal Properties of Compounds Incorporating Cyclobutane, Spiro[3.3]Heptane and Dispiro[3.1.3.1]Decane Rings

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Abstract
A number of esters of structure (I) incorporating the cyclobutane, spiro[3.3]heptane, or dispiro[3.1.3.1]decane rings has been prepared using a diethyl malonate synthesis. Strict comparison of the liquid crystal behaviour amongst the three classes containing a terminal cyano-substituent was not possible because both the cyclobutanes and dispiro[3.1.3.1]decanes are mixtures of cis- and trans-isomers; the spiro[3.3]heptanes are racemic systems. Using preparative hplc, it was however possible to isolate the pure cis- and trans-isomers of two of the cyano-substituted cyclobutane esters (I; R = alkyl, — × — = , Y = CN). From the physical data and the results for the corresponding spiro[3.3]heptane esters, conclusions regarding the effects of these ring systems on liquid crystal behaviour were obtained. The pure cis- and trans-isomers of the cyclobutane ester (I, R = C3H7, — × — = , Y = CN) have been assessed for the trends in both order parameter and viscosity with temperature; the results support the idea that the trans-cyclobutane ring adopts a more planar conformation at higher temperatures.