Anisotropic molecular reorientations of quinuclidine in its plastic solid phase : 1H and 14N NMR relaxation study

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Abstract
14N and 1H NMR relaxation times have been measured in quinuclidine in its plastic phase. These measurements rule out isotropic motion. Correlation times for several anisotropic reorientational models are calculated from these NMR data. The best agreement with the values calculated from neutron scattering experiments (preceding paper) is obtained for a model where the molecules reorient by ± 90° jumps about the crystallographic C4 axes with a residence time of (22.2 ± 2).10-12 s, and by ± 120° jumps about the molecular C3 axes with a residence time of (5.25 ± 2.8).10-12 s, at room temperature. The activation enthalpy is 15.3 kJ. mol.-1 for the ± 90° jumps, and higher for the ± 120° jumps. Translational correlation times have also been measured at high temperature, below the melting point

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