A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state

作者：Popa Laura C; Rheingold Arnold L; Beckmann Peter A^*

来源：Solid State Nuclear Magnetic Resonance, 2010, 38(1): 31-35.

DOI：10.1016/j.ssnmr.2010.06.003

• Solid state NMR relaxation
• X-ray diffraction
• Intramolecular motion
• t-butyl group reorientation
• Methyl group reorientation

We have measured the solid state nuclear magnetic resonance (NMR) (1)H 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.

• 出版日期2010-7