Conformational Study of Hard-core Liquid Crystalline Schiff Bases Containing 1,3,4-Oxadiazole Ring
Juman A. Naser
Department of Chemistry, College of Education for Pure Science, Ibn Al-Haytham, University of Baghdad, Baghdad, Iraq
Yousif I. Mohammed
Department of Chemistry, College of Education for Pure Science, Ibn Al-Haytham, University of Baghdad, Baghdad, Iraq
Taki A. Himdan
Department of Chemistry, College of Education for Pure Science, Ibn Al-Haytham, University of Baghdad, Baghdad, Iraq
Ammar H. Al-Dujaili *
Department of Chemistry, College of Education for Pure Science, Ibn Al-Haytham, University of Baghdad, Baghdad, Iraq
*Author to whom correspondence should be addressed.
Abstract
The relaxed torsion potential of a hard-core Schiff bases of 1,3,4-oxadiazole liquid crystalline series has been studied by molecular modeling techniques. First, conformational search of the molecules was made at molecular mechanics MM+ in order to simplify calculations, so to find the lowest and highest energy conformation structure. In a second stage, geometry optimization calculations of these conformers were performed at the quantum mechanics semi-empirical PM3and RM1 levels in order to obtain more information about the structure and the stability of this core through identification the global minimum energy. Potential energy surfaces (PES) curve has been obtained from plotted the energies against the dihedral angles (θ1, θ3, and θ5). The results show that the core of the molecule did not lie in the same plane. But the π-conjugation is between the segments (A, B) which lay in the same plane and other π-conjugation between segments (C, D) which lay in other plane.
Keywords: Liquid crystal, conformational search, molecular mechanics MM , semi-empirical, parameterization method PM3, dihedral angels