On the Orientation Mechanism of Small Molecules in Liquid‐Crystalline Environments

A general molecular theory for the description of the orientation of small molecules in anisotropic environments is presented. Assuming a second‐order tensorial interaction between some solute property βij and the anisotropy in a liquid‐crystal “field” Fij rigid and non‐rigid contributions to the dipolar and quadrupolar couplings observable by NMR are evaluated. The behaviour of the solutes hydrogen, methane and their deuterated analogues in nematic phases can be described by special cases of this general theory and excellent agreement between observed and calculated anisotropic couplings is obtained. The present results suggest that the coupling between the solute molecular quadrupole moment and the anisotropy in the liquid‐crystal electric field gradient plays a significant role in the orienting process in the case of hydrogen.