NMR Studies of Reorientational Motion in Ethanol and Ethanol Glycerol Mixtures

Deuteron nuclear magnetic relaxation rates 1/T 1 have been measured as a function of temperature for the three labelled ethanols CH 3 CH 2 OD, CH 3 CD 2 OH and CD 3 CH 2 OH. In the supercooled region relaxation rate maxima for the different species were found. The data are discussed in terms of a rotational diffusion model for the overall and the internal reorientations. The slowest motion is performed by the hydroxyl group. Faster reorientation occurs for the ethyl group which behaves as a rather rigid entity in pure ethanol. The internal reorientation of the methyl group has further been studied in ethanol glycerol mixtures. With increasing glycerol content the motion of the ethanol skeleton is slowed down but the internal motion of the CD 3 group about its C 3 symmetry axis maintains its rate. This leads to two relaxation rate steps for the deuterons of the methyl group in these mixtures. The first due to the reorientational motion of the symmetry axis of the CD 3 group occurs in the same temperature range as the relaxation rate maximum of the methylene group. The second step was found at lower temperatures. It belongs to the spinning of the methyl group about its symmetry axis.