Effect of methyl-group reorientation and spin diffusion on spin–lattice relaxation in some choline and acetylcholine halides

Abstract

Spin–lattice relaxation times (T₁) have been measured as a function of temperature for polycrystalline choline chloride and acetylcholine chloride, bromide and iodide. Choline chloride has a single minimum in T₁, but two minima for acetylcholine chloride and bromide have been observed. The T₁ results have been interpreted by considering the reorientational motions of methyl groups about C₃ axes and their role of behaving as sinks to rapid spin diffusion of the other protons in the compounds. The two minima in acetylcholine halides have been shown to be due to the two types of methyl groups in their structures. The activation energies for reorientational motions of methyl groups have been determined.