Order Parameters and Conformation of Nematic p-Methoxybenzylidene-p-n-Butylaniline (MBBA) by NMR Studies of Some Specifically Deuterated Derivatives

  • Y. S. Lee
  • Y. Y. Hsu
  • D. Dolphin


It is known that nematic liquids have a well defined degree of order.1 The order parameter, S, which describes the fluctuation of the molecular axis from the direction of preferential orientation of the molecule, is given by
$$ S = 1/2\left( {3{{\cos }^2}\xi - 1} \right) $$
where ξ is the angle between the long axis of the molecule and the direction of its preferential orientation in the nematic phase. For complete order, cos2ξ = 1 and S=1 as in the case of a crystal, whereas for complete disorder, cos2ξ =1/3 and S=0, representing an isotropic liquid. Thus the order parameter of a nematic will lie between 0 and 1 in a fluid. When a molecule is aligned in a magnetic field, H0, each nuclear magnetic dipole will produce an additional field at neighboring nuclei, the component of which along the direction of H0 together with H0 will result in a total effective field2
$$ {H_{eff}} = {H_o} \pm \alpha \left( {3{{\cos }^2}\,\theta - 1} \right) $$
where a is an interaction field parameter and 6 is the angle between H0 and the line joining the two interacting nuclei.


Nematic Phase Methine Proton Neighboring Nucleus Nematic State Aniline Ring 
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Copyright information

© Plenum Press, New York 1974

Authors and Affiliations

  • Y. S. Lee
    • 1
  • Y. Y. Hsu
    • 1
  • D. Dolphin
    • 1
  1. 1.Department of ChemistryHarvard UniversityCambridgeUSA

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