NMR relaxation studies on testosterone in solution: magnetic field dependence of 13C T1 and anisotropies in the chemical shift
Abstract
The magnetic field dependence of NMR 13C relaxation times have been measured for testosterone in CDCl3. The data were analysed by a computer-assisted method based on the molecular reorientational motion. For the quaternary carbons, contributions from other than the dipole-dipole relaxation mechanisms are separated into the two terms of chemical-shift anisotropy (T1CA) and spin rotation interaction (T1SR). Anisotropies in the chemical shift are derived from T1CA thus separated. These anisotropies are comparable to the existing data, supporting this method of treatment. The barrier to internal rotation is determined for the two methyl groups; it is higher for the 19-methyl by ca. 2 kJ mol–1 than for the 18-methyl.