Orientational order in the 4-n-alkyloxy-4'-cyanobiphenyls

The orientational order of rigid sub-groups for members of the homologous series of 4-n-alkyloxy-4'-cyanobiphenyls, the NOCB, has been studied experimentally and compared with the predictions of the theory proposed by Emsley, Luckhurst and Stockley, [(1982) Proc. R. Soc., A381, 117]. The experimental data were determined from the duterium NMR spectra of compounds containing fully deuteriated chains, and for 3OCB, 4OCB and 6OCB, deuterium was also included in one of the benzene rings. The good agreement obtained between calculated and observed order parameters for these mesogens supports the model proposed for the potential energy of the molecule in the liquid crystal phase. The temperature dependence of the core interaction parameter is obtained and compared with theoretical predictions. The statistical weights of conformers are calculated and it is shown that there is a change in their values on going from the isotropic to the nematic phases. The significance of the ordering matrices for individual conformers is discussed and their relationship to conformationally averaged order parameters is described.