Department of Physics, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA.
Solid State Nucl Magn Reson. 2010 Jul;38(1):31-5. doi: 10.1016/j.ssnmr.2010.06.003. Epub 2010 Jun 16.
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.
我们测量了 5-叔丁基-4-羟基-2-甲基苯硫醚在 NMR 频率为 8.5 和 53 MHz 时，从 93 到 340 K 的固态核磁共振（NMR）1H 自旋晶格弛豫率。我们还通过 X 射线衍射实验确定了分子和晶体结构。弛豫是由甲基和叔丁基基团旋转调制自旋-自旋相互作用引起的，我们将 NMR 动力学参数与结构相关联。数据的成功拟合要求即使在最低温度下，2-甲基基团也能快速旋转（在 NMR 时间尺度上）。两个叔丁基中平面外甲基基团的旋转势垒为 14.3+/-2.7 kJ mol(-1)，叔丁基基团及其平面内甲基基团的旋转势垒为 24.0+/-4.6 kJ mol(-1)。这些不确定度考虑了观察到的 NMR 活化能与模型无关势垒之间的关系以及实验不确定度的不确定性。
