The conformations adopted by the alkyloxy chains in the u,~-bis(4-pheny1oxy)alkanes (PONOP) with 2, 3 and 4 methylene groups in the alkyl chain have been investigated for an isotropic solution in acetone for the compound with N = 2, and for samples dissolved in three nematic solvents for all three compounds.The energy difference, EEc, between gauche and trans conformers produced by rotation about the C-C bond in P 0 2 0 P dissolved in acetone was derived from the scalar coupling constants obtained by analysing the proton spectrum from molecules containing a 13C atom at one C, position. This gave EGc in the range -0.58 to 049 kJmol-'. The deuterium NMR spectra of fully deuteriated samples of the PONOP dissolved in the nematic solvents were used to obtain local order parameters from the quadrupolar splittings. These were compared with values calculated by the mean field method of Emsley, Luckhurst and Stockley (ELS) to give values of E F in the liquid-crystalline phases. The values obtained for Ecc change from being negative for P 0 2 0 P , through zero for P 0 3 0 P to 2.5 kJ mol for P 0 4 0 P . The deuterium NMR data obtained previously for the mesogenic molecules a,o-bis(4-cyanobiphenyloxy)alkanes in their nematic phases have been re-interpreted and it is shown that Egc in these compounds is also strongly dependent on chain length.
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