2014 Nos études expérimentales par RMN de 1H et 2H dans la phase nématique de PAA, PAA-d6 et PAA-d8 suggèrent que le paramètre d'ordre orientationnel S = Szz = 1/2. 3 cos2 03B8 -1 > est suffisant pour expliquer les spectres obtenus. On présente une méthode approximative de calcul des spectres des protons. L'ordre orientationnel des protons dans la molécule PAA est seulement caractérisé par les paramètres Sj qui permettent une description d'ordre intramoléculaire. Abstract. 2014 We have recorded the 1Hand 2H-NMR spectra of PAA, PAA-d6, and PAA-d8. The order parameter S = Szz = 1/2. 3 cos2 03B8 -1 > has been determined from the different types of NMR experiments and shown to be quite sufficient for the interpretation of both proton and deuterium NMR data since the values of the tentatively calculated second order parameter Sxx-Syy (from 2Hresonance of PAA-d8) are very small. From a comparison of the proton NMR spectra of PAA-d6 and PAA and theoretical spectra computed using an approximative procedure for different kinds of intramolecular motions some conclusions are drawn concerning intramolecular mobility of the PAA molecules.
We present the results of proton NMR investigations of the ordering of five members of the homologous series of the p, p'-di-n-alkyloxy-azoxybenzenes in their nematic phases. The difficulties connected with the determination of the accurate absolute value of the order parameter by NMR is critically discussed. The results are compared to those obtained by other methods (Δχ-measurements, X-ray diffraction analysis). The lineshapes of four compounds are calculated theoretically permitting the derivation of conclusions concerning intramolecular mobility and/or order
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