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The binary system tert-butyl iodide–carbon tetrachloride was studied in the liquid and solid phases using 1H and 13C nuclear magnetic resonance spectrometry. An analysis of the methyl 1H and 13C linewidths and spin–lattice relaxation times is reported. The 1H linewidths in the disordered phase (solid I) are governed by 1H–1H dipolar interactions even in the most dilute sample (6.7 mol-%), whereas the 13C linewidths appear to be dominated by 13C–35,37Cl interactions at all concentrations below 70 mol-%. The line narrowing of the 1H resonances is largely caused by translational diffusion of the tert-butyl iodide (TBI) molecules, whereas translational diffusion of the CCl4 molecules dominates the 13C line-narrowing mechanism in most instances. The T1(13C) minimum of solid II moves to lower temperature with increasing dilution, indicating that the reorientational freedom of the tert-butyl group is enhanced by the addition of CCl4. There is a discontinuity in T1 at the melting-point and an abrupt change of T1 at the transition point of the neat and dilute samples of TBI. The measured activation energies and correlation times in solid I suggest that the over-all tumbling motion of the TBI molecules in the inhomogeneous region (solute concentrations higher than 50 mol-%) is markedly retarded by the addition of CCl4.

13 C N.m.r. spin–lattice relaxation data obtained from solutions containing paramagnetic relaxation reagents, such as trisacetylacetonatochromium, can be used for the determination of hydrogen-bond donor acidities of weak carbon acids.