Proton Spin Relaxation in the Chloroethanes

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Abstract
T 1 and T 2 protonrelaxation times were measured for the chloroethanes (CH3CH2Cl, CH3CHCl2, CH2ClCH2Cl, CH3CCl3, CH2ClCHCl2, CH2ClCCl3, CHCl2CHCl2, and CHCl2CCl3) at room temperature as a function of concentration in CS2. The data was extrapolated to infinite dilution. The extrapolated relaxation times were interpreted in terms of two mechanisms: internal dipolar interactions, and scalar coupling between proton and chlorine nuclei. The extrapolated relaxation times indicated that the dipolar correlation times increased as the number of chlorines increased, while the chlorine relaxation times decreased as the number of chlorines increased. Internal dipolar correlation times were computed from the extrapolated T 1 relaxation times. The relative trends of the reorientational correlation times were explained equally well by the BPP viscosity model and an inertial model due to Steele. The inertial model predicted correlation times which were too low by a factor of 2, whereas the BPP model predicted correlation times too high by an order of magnitude. This was interpreted to mean that the reorientational motions of the chloroethanes at infinite dilution in CS2 are controlled more by the moments of inertia of the chloroethanes than by the frictional forces of the solvent.