Nuclear Magnetic Relaxation in t-Butanol: Molecular and Internal Methyl Rotation

Abstract

The correlation function of the randomly molecular reorientation, and internal (around some bond in the molecule) rotation, is calculated and discussed, assuming that both processes in the liquid are diffusional. The contribution of the internal rotation to the nuclear magnetic relaxation process is effective only when its rate is about the same order of magnitude as the molecular one. When the internal rotation is very much slower, or very much faster compared with the molecular rate of rotation (in the extreme narrowing limit), then its correlation time vanishes in the expression for the spectral density. Only when the ratio of the internal rotation correlation time τc′ to the molecular reorientation correlation time τc is between about 10 to 0.1, is it possible to obtain information about the internal rotation in the molecule from magnetic relaxation measurements. T1(D) of the two deuterated species of tert-butanol, (CH3)3–COD and (CD3)3–COH were measured, and by applying the formalism of the combined correlation function, it was possible to separate the correlation times for the molecular and the internal methyl rotation.