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 (T₁^CA) and spin rotation interaction (T₁^SR). Anisotropies in the chemical shift are derived from T₁^CA 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.