NMR Studies of the Reorientational Motion in Methanol and Methanol‐Water Mixtures

Deuteron nuclear magnetic relaxation rates 1/T1have been measured as a function of temperature for the labelled methanols CH3ODand CD3OH in the neat liquids and in mixtures with H2O and D2O. It was possible to supercoole the mixtures to sufficiently low temperatures to observe relaxation rate maxima. The data are discussed in terms of a rotational diffusion model for the overall and the internal rotation. — A rather slow reorientation is performed by the hydroxyl group of methanol. This motion is strongly coupled to the fluidity of the liquids and is markedly slowed down (at constant temperature) with increasing water content. On the other hand, the methyl group performs a rather free rotation which is not influenced by the mixture composition. — A short discussion of the fast methyl rotation in terms of an “extended” internal diffusion model is given.