title: Proton NMR study of molecular motion in solid cortisone.
abstract: 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.
authors: Department of Physics, University of Florida, Gainesville 32611.
authors: E R
authors: ER
authors: Andrew
authors: M
authors: M
authors: Kempka
mesh_terms: D003348:Cortisone / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy
chemical_list: D003348:Cortisone