Methyl and t-butyl group rotation in a molecular solid: 1H NMR spin-lattice relaxation and X-ray diffraction

Abstract

We report solid state ¹H nuclear magnetic resonance spin-lattice relaxation experiments and X-ray diffractometry in 2-t-butyldimethylsilyloxy-6-bromonaphthalene. This compound offers an opportunity to simultaneously investigate, and differentiate between, the rotations of a t-butyl group [C(CH₃)₃] and its three constituent methyl groups (CH₃) and, simultaneously, a pair of ‘lone’ methyl groups (attached to the Si atom). The solid state ¹H relaxation experiments determine activation energies for these rotations. We review the models for the dynamics of both ‘lone’ methyl groups (ones whose rotation axes do not move on the NMR time scale) and models for the dynamics of the t-butyl group and its constituent methyl groups (whose rotation axes reorient on the NMR time scale as the t-butyl group rotates).