J. Phys. II France 1 (1991) 209-223
On the interpretation of NMR data of non-rigid molecules in nematic phases: a serve test of the single conformation modelD. Galland and F. Volino
Département de Recherche Fondamentale, SPH/PCM, C.E.N.G., BP 85 X, 38041 Grenoble cedex, France
(Received 01 August 1990, revised 29 October 1990, accepted 31 October 1990)
The large sets of dipolar and quadrupolar NMR data of Celebre et al. [10, 11] for four non-rigid molecules based on the ethoxybenzene moiety dissolved in a nematic solvent are analyzed in terms of a model in wich the molecules are assumed to exist essentially in one conformation. It is found that this model, in wich the number of adjustable parameters is less than the number of independent data, can describe very well the whole set of data for each of these molecules. The conformational parameters and the five elements of the order tensor are unequivocally deduced, with high accuracy, for three molecules, and only estimated for the fourth one. The conformations and orders are found to be similar for the four molecules, and the relative values of the two order parameters in agreement with the predictions of mean field theories. These results are contrasted with those of [10, 11] in wich many different conformations are assumed to exist. The assumptions concerning the possible conformations and the use of the ELS model  made in this approach are criticized, and it is argued that our (simpler) single conformation model probably provides a more realistic description of a liquid at the molecular scale.
© Les Editions de Physique 1991