Nuclear magnetic resonance absorption and relaxation study of tert-butylamine and tert-butylamine clathrate deuterate

Abstract

Proton magnetic resonance absortion (at 16 MHZ) and spin-lattice relaxation time (at 26.46 MHz) measurements have been carried out for pure tertiary-butylamine, and tertiary-butylamine clathrate deuterate from 77°K to the melting points of these compunds. The absorption line measurements on t-butylamine show that the second moment changes from values expected for a rigid lattice to a plateau value consistent with the three methyl groups and the t-butyl group rotating at temperatures near 150°K. In the case of the deuterate, t-butylamine exhibited much more freedom of motion as judged from the second moment measurements. The motional behavior ranges from methyl and t-butyl group rotation to isotropic rotation of the whole molecules. The proton spin-lattice relaxation measurements on t-butylamine exhibited a broad minimum of 16 msec, which is thought to be mainly due to methyl group reorientation. An activation energy of <(3.2± 0.1) kcal/mole was calculated from T1 measurements at various temperatures and this is associated with the barrier hindering methyl group reorientation. The clathrate deuterate of this amine showed a very broad minimum of (32± 1) msec which is thought to arise from three types of motion; namely, methyl and t-butyl group rotation as well as isotropic rotation of the whole molecule. The limiting activation energies in the deuterate of (1.73± 0.03) kcal mole−1 and (2.5± 0.02) kcal mole−1 and therefore expected to be determined by methyl and t-butyl rotation and by t-butyl and isotropic rotation, respectively.