This thesis consists of the synthesis of new liquid crystalline compounds 2-thiobutanoyl-5-[4-(4´-methoxybenzylideneamino)phenyl]1,3,4-oxadiazole 1e, 4-[4´-methoxyben- zylideneamion)benzoyloxy]propylbenzoate 2d and two new homologous series derived from 2,5-bis-[4-amino phenyl]-1,3,4-oxadiazole 3d, these are 2,5-bis-[4-(4´-alkoxybenzylideneamino)phenyl]-1,3,4-xadiazole 3e1-3i1 and 2,5-bis-[4-(4´-alkoxybenzanilide)phenyl]-1,3,4-oxadiazole 3e2-3i2.(3e2,f2,g2,h2, i2) The characterization of the synthesized compounds using FTIR and 1HNMR spectroscopy and the liquid crystalline properties of the prepared compounds which were verified using differential scanning calorimeter (DSC) and hot-stage polarizing microscope were discussed. The relation between the liquid crystalline behavior with chemical constitution was discussed on the basis of introduction of the heterocyclic unit, i.e., 1,3,4-oxadiazole. It was found that the replacement of aromatic rings by heterocyclic moiety play an important role in effecting the planarity, polarizibility and linearity which in turn effecting the thermal liquid crystalline stability. Compounds 1e and 2d were used as stationary phases in gas chromatography for separation of positional isomer hydrocarbons (o-, m-, p-cresol) and poly aromatic hydrocarbons ( naphthalene, flourene, phenanthrene and anthracene). Stationary phases for gas chromatography were prepared by loading the above compounds on solid support ( chromosorb W/AW 60-80 mesh) at 20%. These stationary phases were packed on glass gas chromatographic columns. A gas- liquid chromatographic study of the interaction and elution characteristics of positional isomer hydrocarbons and poly aromatic hydrocarbons using liquid crystalline phases and at different column temperatures of 140ºC-300ºC for 2-thiobutanoyl-5-[4-(4´-methoxybenzylideneamino)phenyl ]1,3,4-oxadiazole 1e and 140ºC -260ºC for 4-[4´-methoxybenzylideneamion)benzoyloxy]propyl benzoate 2d.The best chromatographic conditions for the separation of hydrocarbons were characterized by measuring column efficiency Neff, resolution R, and selectivity factors α in order to assess the performance and separation ability of these columns. It was found that best chromatographic performance can be achieved with operating temperature at which the thermal stability of the nematic mesophase starts to form. Specific retention volume V'R calculated from the experimental retention time. Abnormal Chromatographic behavior, has been observed, an increase in V'R and an important separation of aromatic hydrocarbons above the nematic temperature. From the plots of ln V'R versus 1/T (K-1), it is concluded that this behavior may be attributed to the penetration of solutes (aromatic hydrocarbons) through the ordered structure of the mesophase and the rod-like molecules of liquid crystals stationary phases. The study also included measurements of activity coefficient at infinite dilution and thermodynamic functions, Gibbs free energy ∆G, enthalpy ∆H and entropy ∆S of the separated hydrocarbons at the optimum chromatographic condition. The result showed that the dissolution of solutes (cresol isomers and poly aromatic hydrocarbons) on the stationary phases were spontaneous.
