| dc.description.abstract | In the first series, four new series of unsymmetric isoxazoles and 1,3,4-oxadiazoles were prepared, characterized and their mesomorphic properties investigated. Isoxazoles were obtained by condensationcyclization of –diketones with hydroxylamine hydrochloride in refluxing THF, while 1,3,4-oxadiazoles were obtained from hydrazine–carboxylate in refluxing POCl3. Two single crystallographic structures were determined by Xray crystallographic analysis. A correlated dimeric structure was formed by Hbonds in isoxazoles 1a (n = 6), leading to an more elongated structure required for the formation of mesophases. All compounds 1ac formed N, SmA or/and SmC phases. In contrast, compounds 1d exhibited columnar phases, and an Ncell = 14.6 obtained from powder XRD data indicated that a correlated structure formed by four molecules was probably induced in Colh phases. The better mesomorphic behavior formed in 1a than 1b might be attributed to stronger intermolecular interactions and higher polarization induced in isoxazoles 1a.
In the second series, A new system of isoxazole contaning function group of aldehyde, performed reaction of Schiff base then exhibiting mesomorphic properties was synthesized and their mesomorphic properties examined. 4a and exhibited N, and SmC phases. Increasing alkoxy chains would transform rod like liquid crystal to columnar phases. Two single crystallographic structures were determined by Xray crystallographic analysis. Both CH-π interaction and π-π interaction were discovered in structure 4a (n = 6) and 5a (n = 6),which is critical force to maintain mesogen formed.
Metallomesogen is major sublect in third serie, a new type of mesogenic heterocyclic of ligand with diketone group exhibited N, SmC phase, Their mesomorphic behavior was dependent on the carbon lengths attached. The crystallographic structures of similar structure with 6a amd copper cmplex of 6a and were determined by Xray crystallographic analysis. Discovered when ligand form mesogen combining hydrogen bond which would disappear when metal bond formed.
In this work, the synthesis, characterization and mesomorphic properties of a new series of compounds 1- 2 are described. These compounds contain two heterocyclic rings, one pyrazole and the other isoxazole. These compounds were characterized by 1H and 13C-NMR spectroscopy. A single crystal of the mesogenic compound 2 (n = 6) suitable for crystallographic analysis was obtained and its crystal and molecular structure was determined by means of X-ray structural analysis. It crystallizes in the triclinic space group P-1, with a = 11.1719(2) Å, b = 14.2409 (3) Å, c = 17.9131(4) Å, and Z = 4.
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