ALKYL CHAINS IN A NEMATIC FIELD .1. A TREATMENT OF CONFORMER SHAPE

A theory is presented for the explicit inclusion of molecular shape anisotropy and flexibility in the description of the interactions associated with alkyl chains in the nematic phase. This description yields quantitative agreement with observed deuterium quadrupolar and dipolar NMR splittings, using the conventional parameters of the rotational isomeric state model for the chain. Orientational correlations between neighboring chain segments are introduced to distinguish conformations which are energetically indistinguishable in previous single segment interaction models. A detailed analysis of the deuterium NMR observations on decane-d22 dissolved in a nematic solvent is presented. The new approach gives clear insights into the relevant aspects of flexible molecules experiencing a uniaxial constraint and enables us to understand the shortcomings of previous efforts to model flexible molecules in the nematic phase. © 1990 American Chemical Society.