Molecular dynamics in solid anhydrous beta-estradiol studied by 1H NMR.

Proton second moment and spin-lattice relaxation times T1 and T1p in solid anhydrous beta-estradiol are measured as a function of temperature. The results show that the C3 reorientation of the single methyl group provides the mechanism dominating relaxation at low temperatures and reveal the existence of a conformational motion of the carbon skeleton dominating relaxation at high temperatures. The activation energies of the respective motions are found to be 9.3 and 37.3 kJ/mol.

Molecular dynamics in polycrystalline testosterone studied by proton NMR.

Polycrystalline testosterone (17 beta-hydroxy-4-androsten-3-one, C19H28O2) has been investigated by proton NMR methods between 70 K and the melting point 428 K. Reductions in dipolar second moment and two well-resolved minima in the spin-lattice relaxation time measured at 25 MHz are ascribed to reorientation of the two methyl groups in the molecule. Activation energies Ea characterizing the motions were 6.1 +/- 0.5 and 11.9 +/- 0.9 kJ/mol; the pre-exponential time factors tau 0 were (2.3 +/- 0.1) x 10(-13) and (2.85 +/- 0.2) x 10(-13) s, respectively.

Proton relaxation NMR study of polycrystalline progesterone.

Polycrystalline progesterone (4-pregnene-3,20-dione, C21H30O2) has been investigated by proton NMR methods between 80 and 350 K. A reduction in dipolar second moment is ascribed to methyl group reorientation. Minima in the spin-lattice relaxation time found in measurements at five frequencies from 7 to 200 MHz are attributed to reorientation of two of the three methyl groups in each molecule, characterized by activation energy Ea = 10.9 +/- 0.8 kJ/mol and tau o = (2.3 +/- 0.2) x 10(-13) s. Additional relaxation at lower temperatures is attributed to reorientation of the third methyl group with Ea approximately 3.4 kJ/mol. Measurements were also made of relaxation in the rotating frame.