The energy barrier to reorientational motion of the trifluoromethyl group in lithium trifluoromethanesulphonate and its complex with poly(ethylene oxide): a comparison between modelling and NMR relaxation measurements

Molecular modelling is used to calculate the barrier heights to reorientation for the trifluoromethyl group, CF3, in both lithium trifluoromethanesulphonate, LiCF3SO3, and the crystalline complex of this salt with poly(ethylene oxide), PEO. The calculated barrier heights are compared with those determined from 19F spin–lattice relaxation studies. In the case of LiCF3SO3, fluorine–fluorine non-bonded interactions are shown to play a dominant role in determining the barrier height to CF3 group reorientation and optimised Lennard-Jones parameters for this interaction are determined. In the crystalline complex, PEO3·LiCF3SO3, it is suggested that CF3 group reorientation is strongly influenced by segmental motions of the PEO chain.