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Abstract
A theoretical analysis has been carried out to determine the configurational preference of a pair of 4′ - Nitrophenyl 4-Octyloxybenzoate (NPOB) molecules with respect to translatory and orientational motions. 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 - Schrodinger perturbation theory along with multicentered- multipole expansion method, has been employed to evaluate long-range intermolecular interactions while “6-exp” potential function has been assumed for shortrange interactions. Accuracies upto 0.1A° in translation and 1° in rotation have been achieved. On the basis of stacking, in-plane and terminal interactions energy calculations, all possible geometrical arrangements between molecular pair have been considered. Probability of occurance of a particular configuration has been calculated in vacuum and in dielectric medium using Maxwell- Boltzmann formula. Further, the flexibility of various configurations has been studied in terms of the variation of probability due to small departures from the most probable configuration. It has been observed that the molecule has strong preference for stacking through a particular face, while the other configurations such as stacking through the other face, in- plane and terminal interactions show, in general, an aligned structure along its long molecular axis. The probabilities are redistributed in dielectric medium and there is considerable rise in the probabilities of interactions. The mesogenic character of the molecule has also been correlated with the parameters introduced in this paper.
