NMR line-width, self-diffusion and relaxation studies of neopentanol in liquid and solid phases

The translational and rotational dynamics of the liquid and disordered (solid I) phases of neopentanol are investigated using high-field multinuclear NMR. The extensive line-narrowing of the ¹H resonances for solid I is ascribed to the onset of translational diffusion whereas the line-narrowing of the deuteron and carbon-13 signals is dominated by molecular reorientations. The activation energy of the molecular self-diffusion is 34 and 71 kJ mol⁻¹ for the liquid and solid I phases, respectively. The self-diffusion coefficient of solid I is 3.2 × 10⁻¹³ m² s⁻¹ at the melting point.

A thorough analysis of the multinuclear T₁ data is presented. The activation energy of the overall tumbling motion in the liquid and solid I phases, obtained from the hydroxyl deuteron T₁ data, is 36 and 52 kJ mol⁻¹, respectively. The internal reorientations have a profound effect on the spin-lattice relaxation times of the methyl and methylene groups by reducing the effective correlation time by an order of magnitude relative to the overall tumbling motion in solid I. The long correlation time (22 and 58 ps of liquid and solid neopentanol at the melting point) and high activation energy suggest that the overall tumbling motion in the liquid and disordered phases involves hydrogen-bonded aggregates.