Symmetric 3,5-Pyrazole and Isoxazole Heterocycles Comprising a Bent Core Unit: Synthesis and Mesomorphic Characterisation

The synthesis and characterisation of some new liquid crystalline (LC) heteroaromatic compounds containing the five-membered pyrazole/isoxazole rings is reported. Some of the compounds exhibited enantiotropic LC properties. The transition temperatures and LC textures of the mesophases were determined using polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray studies. The five-membered heterocyclic compounds with the pyrazole core exhibit smectic C (SmC) phase, whereas isoxazoles show SmC and nematic (N) phases

4-[2-(Trimethylsilyl) Ethynyl]Benzoates: Synthesis and Evaluation for Mesomorphic Properties of some Novel Calamitic Molecules

A series of novel terminal trimethylsilylacetylene benzoate derivatives with various linking groups were synthesized using Friedel-Craft's O-acylation reaction. The chemical structures of the novel4-[2-(trimethylsilyl)ethynyl]benzoates were confirmed by standard spectroscopic techniques. The compounds were investigated for their liquid crystalline properties employing polarised optical microscopy and differential scanning calorimetry. The esters 5c – 5f, 5h and 5n possessing three phenyl rings exhibited liquid crystalline property of SmA/SmC phases with wide thermal range

Synthesis of some Novel Aromatic Alkynyl Silanes: Mesomorphic Characterization of Ethynyl-Substituted Rod-Shaped Molecules

The synthesis and characterization of 10 new rod-shaped substituted benzoates possessing the 4-(2-trimethylsilyl)ethynyl group in terminal phenyl position is reported employing the simple and efficient Sonogashira cross-coupling and DCC esterification. 4′-Dodecylbiphenyl-4-carboxylic(2-trimethylsilylethynyl)-phenyl ester (3i), 4-(4′-hexadecyloxybenzyloxy) carboxylic-4-trimethylsilanylethynyl-phenyl ester (3j), and 1,4-bis(4-(pentyloxy)phenyl)buta-1,3-diyne (7) compounds were evaluated for liquid crystal property

New mesogenic compounds possessing a biphenyl ester and ether moiety comprising 1,3-dimethylbarbituric acid: synthesis, characterisation and mesomorphic studies

New substituted derivatives of 5-vinyl-1,3-dimethylbarbituric acid were synthesised and evaluated for liquid crystal properties. Two sets of molecules were prepared. One end of all the molecules possesses the 1,3-dimethylbarbituric core. The first set comprises biphenyl ethers, 4a–n and the second set biphenyl esters, 5a–g. Liquid crystalline properties were investigated by POM and DSC techniques. All the compounds exhibited enantiotropic smectic A and nematic mesophases. The LC properties were found to depend on the spacer and terminal alkoxy- chain and alkoxy- ester moiety of the molecules. Smaller alkyl chain members showed a smectic phase, while higher alkyl chain members showed a nematic phase

Ultrasonic synthesis and crystal structure analysis of two trimethylsilyloxy-substituted bicyclo[2.2.2]octene derivatives

The compounds: 11-trimethylsilyloxy-1,2,3,4,4a,9a-hexahydro-1,4-etheno-anthraquinone and 4-benzyl-8-trimethylsilyloxy-4-aza-tricyclo[5.2.2.0]undec-8-ene-3,5-dione were synthesized by the Diels–Alder [4πs +2 πs] cycloaddition reaction of 2-(trimethylsilyloxy)-1,3-cyclohexadiene with naphthaquinone and N-benzylmaleimide under ultrasonic conditions. The crystal structure analysis was done using single crystal X-ray diffraction method. In both the compounds, the trimethylsilyloxy- and naphthaquinone/ N-benzylmaleimide moieties are endo- to the bicyclic ring

Synthesis and comparative studies of phase transition behaviour of new dimeric liquid crystals consisting of dimethyluracil and biphenyl cores

A new homologous series of mesogens containing 6-amino-1,3-dimethyluracil moiety have been synthesized. The structures of the compounds were characterised by elemental analysis, FT-IR, 1H and 13C NMR spectroscopic techniques. Their mesomorphic properties were studied by polarising optical microscopy attached to a heating stage. Microscopy data were supported with transition temperatures and enthalpy change values obtained from the differential scanning calorimetry analysis. The studies have shown that the mesomorphic properties of the compounds are dependent on the lengths of alkoxy-spacers. Compounds 4a-f with a shorter alkoxy-spacer chain (n = 6) exhibited smectic A phase, while compounds 4g-r with a alkoxy-spacer chain (n = 8 or 10) displayed nematic phase

Synthesis mesomorphic and theoretical studies of some new unsymmetrical dimeric ethers of 6-amino-1,3-dimethyluracil and biphenyl cores

New sets of unsymmetric calamitic molecules with uracil unit at one end and biphenyl core at another end were synthesized. Liquid crystal property of these molecules was investigated by POM and DSC techniques. All compounds exhibit LC property depending on the spacer and terminal alkoxy chain of the molecules. First set shows smectic phase in lower members and nematic phase appeared in higher members. The second set favour nematic liquid crystalline phase with respect to spacer alkyl chain length. Molecules are escaped from the planarity as a result disturbing the layer stacking leads to nematic phase in higher analogues. Theoretical studies have been performed for all the compounds and are found to be in agreement with the results of the current studies

Synthesis of some novel 4-aza-tricyclo5.2.2.0 2,6undecane-3,5,8-triones from 2-trimethylsilyloxy-1,3-cyclohexadiene and 1-methoxy-1,3-cyclohexadiene

The synthesis and characterization of nine novel Diels-Alder cycloadducts: the 4-azatricyclo5.2.2.0 2,6 undecane-3,5,8-triones using 2-trimethylsilyloxy-1,3-cyclohexadiene and 1-methoxy-1,3-cyclohexadiene is reported. The isolated yields of the pure cycloadducts range between 75 to 95%