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- W2037541185 abstract "Proton n.m.r. relaxation time measurements have been made on bicyclo [2.2.2] octane (BCO) and bicyclo [2.2.2] oct-2-ene (BCOE). Measurements for each sample were made throughout the plastic and brittle phases, down to 77 K. The results have been interpreted in terms of the various molecular motions occurring in the solid. Below the plastic-brittle phase transition point anisotropic molecular reorientation appears to occur. The activation enthalpy for this motion is 17.1±1.2 and 17.3±1.2 kJ•mol −1 in BCO and BCOE respectively. Above this phase transition a rapid endospherical reorientation is observed and relaxation time measurements yield an activation enthalpy of 7.7±0.9 and 7.4±0.6 kJ•mol −1 for this process in BCO and BCOE respectively. At higher temperatures molecular self-diffusion becomes the dominant controlling mechanism for T 1 ρ and T 2 . The activation enthalpy for this process is found to be 95.1±2.1 and 66.8±6.3 kJ•mol −1 in BCO and BCOE respectively. Correlation times, τ, for translational and reorientational motion are evaluated. The results and mechanisms for reorientational and translational motion are discussed in relation to the respective crystal structures and thermodynamic properties of the materials. Results related to the molecular reorientation in phase I of BCO are in quantitative agreement with those of incoherent quasi-elastic neutron scattering. The unit cell of the plastic phase I of BCOE which has been investigated by X-ray powder diffraction is f.c.c. with a 0 =0.908±0.002 nm Mesures des temps de relaxation de RMN des protons couvrant tout le domaine de temperature de 77 K jusqu'au point de fusion. En dessous de la transition de phase I-II subsiste un mouvement de reorientation moleculaire anisotrope, dans la phase plastique, on observe une reorientation quasi spherique, tandis qu'aux temperatures plus elevees, l'autodiffusion devient le mouvement controlant la relaxation" @default.
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- W2037541185 date "1985-01-01" @default.
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- W2037541185 title "Molecular motion in solid bicyclo[2.2.2]octane and bicyclo[2.2.2]oct-2-ene studied by nuclear magnetic resonance" @default.
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- W2037541185 doi "https://doi.org/10.1051/jphys:01985004602027100" @default.
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