Self-diffusion in a series of plastic organic solids studied by NMR

Proton nuclear magnetic resonance relaxation times and linewidth measurements have been made on five polycrystalline organic compounds, triethylenediamine, 3-azabicyclononane, norbornane, norbornylene and norbornadiene. Measurements for each sample were made throughout the plastic crystal phase. The results are analysed in terms of molecular motion. Correlation times τ and activation enthalpies for translational self-diffusion of molecules are evaluated: triethylenediamine τ=7·6×10^?19 exp (96·4/RT)s, 3-azabicyclononane τ=1·7×10^?16 exp (83·6/RT)s, norbornane for 131K<T<306 K, τ=4·6×10^?15 exp (54·5/RT)s for 306K<T<360K, τ=1·1×10^?16 exp (64·8/RT)s, norbornylene, τ=4·×10^?15 exp (48·6/RT)s and norbornadiene τ=6·8×10^?15 exp (39·9/RT)s, where R is the gas constant in units of kJ K^?1mol^?1. The results and mechanism of diffusion are discussed in relation to the thermodynamic properties of the materials.