Proton and "C line widths and spin-lattice relaxation times, TI, have been measured for liquid and solid 2,2-dichloropropane (1) and 2,2-dibromopropane (2). Molecular self-diffusion, with activation energies in the range 18-24 kJ mol-', is responsible for the considerable line narrowing observed for the NMR spectra in solid I of these substances. The NMR data reveal a previously unreported phase transition point at 208 K for 2. An analysis of the proton and 13C TI times in both the liquid and solid phases is reported. Effective correlation times, activation energies and pre-exponential factors for the appropriate motions have been obtained from the Arrhenius equation. The proton and I3C spin-lattice relaxation mechanisms in the liquid and solid I phases are governed by overall molecular reorientations, with activation energies in the range 9-11 kJ mol-'. The rotational correlation time increases slightly at the liquid + solid I boundary from 3.2 to 3.6 ps for 1 and from 5.1 to 5.4 ps for 2. The correlation time is observed to decrease by five orders of magnitude at the solid I + solid I1 transition point of 2. The dominant motion causing spin-lattice relaxation in phase I1 is methyl group reorientation with an activation energy of 18 kJ mol-'.