On 2H NMR and molecular motion of t-butyl groups in solidsa)

Although 1H NMR generally cannot be used to distinguish between methyl group (C3) rotation, and rotation of the whole t-butyl group about its threefold axis (C′3 motion), 2H NMR line shapes are shown to be quite diagnostic as to which motion is present. In agreement with neutron scattering results C′3 motion was shown to be faster than C3 motion for t-butyl chloride and t-butyl bromide at ∼100 K. Also, C′3 motion is faster than C3 motion for trimethylamine in its 10.25 hydrate.