Andrew E R, Kempka M
Department of Physics, University of Florida, Gainesville 32611.
Solid State Nucl Magn Reson. 1993 Oct;2(5):261-4. doi: 10.1016/0926-2040(93)90006-9.
Polycrystalline cortisone (17,21-dihydroxy-4-pregnene-3,11,20-trione, C21H28O5) has been investigated by proton NMR methods between 56 and 400 K at 14 and 25 MHz. Reductions in second moment and two very well-resolved minima in the spin-lattice relaxation time at both frequencies are attributed to reorientation of the two methyl groups on carbons 18 and 19. The data are very well fitted over the entire temperature range to the Kubo-Tomita dipolar relaxation theory using the same parameters at both frequencies. Activation energies Ea characterizing the hindrances to the two methyl reorientations were 5.9 and 15.5 kJ/mol, an unusually large difference. The relaxation constants were 6.4 and 7.9 x 10(8) s-2.
多晶型可的松（17,21 - 二羟基 - 4 - 孕烯 - 3,11,20 - 三酮，C21H28O5）已通过质子核磁共振方法在56至400K温度范围内、14和25MHz频率下进行了研究。在两个频率下，二阶矩的降低以及自旋晶格弛豫时间中两个分辨率良好的极小值归因于碳18和19上两个甲基的重取向。在整个温度范围内，使用相同参数在两个频率下将数据很好地拟合到久保 - 富田偶极弛豫理论。表征两个甲基重取向障碍的活化能Ea分别为5.9和15.5kJ/mol，差异异常大。弛豫常数分别为6.4和7.9×10(8)s-2。
