Molecular order of mesogenic compounds (CCHs) at phase transition temperature - A computational analysis

A computational analysis has been carried out to determine the configurational preference of a pair of three homologous, trans, trans4-'-alkylbicyclobexyl-4-carbonitriles (cyclohexylcyclohexanes, CCHs) with alkyl group: propyl (CCH3); pentyl (CCH5); heptyl (CCH7) with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. Modified Rayleigh-Schodinger perturbation theory along with multicentred-multipole expansion method has been employed to evaluate the long-range intermolecular interactions while a '6-exp' potential function has been assumed for short-range interactions. The interaction energy values obtained through these computations were used to calculate the probability of each configuration at phase transition temperature using Maxwell Boltzmann formula. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of molecular pairs of CCH3, CCH5 and CCH7 have been considered and the most favourable configuration of the pairing has been obtained. The results have been correlated with the parameters introduced in this paper. (C) 2003 Elsevier Science B.V. All rights reserved.