Synthesis,regioisomerism and characterization of unsymmetrical alkenyl-terminated isoxazole liquid crystals |
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Authors: | David H. Brown Peter Styring |
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Affiliation: | Department of Chemical and Process Engineering, The University of Sheffield, Mappin St, Sheffield S1 3JD, UK |
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Abstract: | Two series of unsymmetrical diphenyl-1,3-diketones, each species bearing one terminal alkene, have been synthesized. These diketones have been converted into their respective unsymmetrical diphenylisoxazoles [3(5)-(4-ω-alkenyloxyphenyl)-5(3)-(4-alkoxyphenyl)isoxazoles] which have been isolated as equal mixtures of two regioisomers, due to 3,5- and 5,3-substitution of the isoxazole ring. The mesogenic properties of the isoxazole liquid crystals have been studied by polarizing optical microscopy and DSC. The effect of increasing alkoxy chain length (C6-C10) on the properties of the two series of isoxazoles has been examined. The isoxazoles show enantiotropic smectic C, smectic A and nematic mesophases. A detailed 1H and 13C NMR spectroscopic study has examined both the 1,3-diketones and isoxazoles. Proximity of the terminal alkene to the diphenyl core can greatly affect the complexity of the 13C NMR spectra. |
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Keywords: | synthesis pyridine-containing compounds liquid crystals thermal analysis |
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