Dielectric and optical properties of polymer-liquid crystal composite

Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared.     

Naphthyl azomesogens with lateral chloro groups

A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related series to evaluate the effect of lateral chloro group and its position on mesomorphism This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003.     

Reactions of 1,4-bis(tetrazole)benzenes: formation of long chain alkyl halides

The reactions of 1,4-bis[2-(tributylstannyl)tetrazol-5-yl]benzene with α,ω-dibromoalkanes were carried out in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazole. This led to the formation of several alkyl halide derivatives, substituted variously at N1 or N2 on the tetrazole ring. The crystal structures of 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (2-N,2-N′), 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (1-N,2-N′) and 1,4-bis[(2-(8-bromooctyl)tetrazol-5-yl)]benzene (2-N,2-N′) are reported. Further discussion involves the structure of 1,4-bis[2-(6-bromohexyl)-2H-tetrazol-5-yl]benzene (2-N,2-N′) previously reported.     

Microwave Induced Bismuth Trichloride Catalysed Beckmann Rearrangement of Oximes

A new and efficient method for the rearrangement of oximes 1 has been achieved by a simple reaction of a ketoximes with bismuth trichloride under microwave irradiation in the solid state.     

Microwave Assisted Rupture of Furoxans to Nitrile Oxides and Intermolecular Capture by Dipolarophiles

3,4-Diaroylfuroxans 1 react with various dipolarophiles 3 under microwave activation to afford the cycloadduct 4 instead of the expected isoxazole 5 in good yields in the absence of solvent.     

Ammonium Sulphate—Magnesium Promoted Selective Reduction of Aromatic Nitro Compounds

Various nitroarenes and 2,1,3-benznooxadiazole-1-oxides were selectively and rapidly reduces to their corresponding amino and diamino compounds respectively in high yields using (NH₄SO₄-Mg/A1/Bi, a new reduction system.     

Mesogenic properties and the effect of 1,2,4-trisubstitution on the central benzene nucleus of a three-ring mesogen

Four mesogenic homologous series have been synthesized by fixing a rigid 4-substituted phenylazo group to a resorcinol moiety. In series I and II, one phenolic -OH group is esterified by 4-n-alkoxybenzoyl groups; in series III and IV both the phenolic -OH groups are esterified by 4-n-alkoxybenzoyl groups. All the homologues of series III and IV exhibit low melting smectic C phases. Monoesters of series I and II, having free lateral hydroxy group with strong hydrogen bonding, exhibit high temperature nematic phases. The effect of different substituents on mesomorphic properties is discussed. One homologue of series III was doped with a chiral dopant and its spontaneous polarization evaluated.     

Effect of a lateral methyl group on azo-mesogens containing the naphthalene moiety

Two mesogenic homologous series, 2-[4-(4-n-alkoxybenzoyloxy)-2-methylphenylazo]-naphthalenes (I) and 2-[4-(4-n-alkoxybenzoyloxy)-3-methylphenylazo]naphthalenes (II) with a lateral methyl group have been synthesized. Both series are purely nematogenic. The mesomorphic properties of both series are compared with each other and also with the properties of other structurally related series to evaluate the effect of the lateral methyl group on mesomorphism. The chiral nematic (N*) mesophase was induced in the system by doping with a derivative of naturally occurring chiral menthol.