A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state
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Solid State Nuclear Magnetic Resonance
We have measured the solid state nuclear magnetic resonance (NMR) 1H spin-lattice relaxation rate from 93 to 340 K at NMR frequencies of 8.5 and 53 MHz in 5-t-butyl-4-hydroxy-2-methylphenyl sulfide. We have also determined the molecular and crystal structures from X-ray diffraction experiments. The relaxation is caused by methyl and t-butyl group rotation modulating the spin–spin interactions and we relate the NMR dynamical parameters to the structure. A successful fit of the data requires that the 2-methyl groups are rotating fast (on the NMR time scale) even at the lowest temperatures employed. The rotational barrier for the two out-of-plane methyl groups in the t-butyl groups is 14.3±2.7 kJ mol−1 and the rotational barrier for the t-butyl groups and their in-plane methyl groups is 24.0±4.6 kJ mol−1. The uncertainties account for the uncertainties associated with the relationship between the observed NMR activation energy and a model-independent barrier, as well as the experimental uncertainties.
Lauren C. Pope, Arnold L. Rheingold, and Peter A. Backmann. 2010. "A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state." Solid State Nuclear Magnetic Resonance 38.1: 31-35.
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