N.M.R. study of molecular dynamics and phase transitions in solid 2-methyl-2-propanol

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Abstract
Proton second moment and spin-lattice relaxation times (T 1 and T 1ρ) have been studied in solid 2-methyl-2-propanol in the temperature interval 77 K to the melting point. The data at low temperatures are satisfactorily explained in terms of simultaneous methyl and t-butyl motions. The activation energies of these motions are of 22·3 and 13·2 kJ mol-1, respectively. At high temperatures the relaxation, particularly T 1ρ, is influenced by translational diffusion. The energy barrier to this process is estimated roughly to be of about 137 kJ mol-1. The results confirm the existence of the phase transition at around 287 K and indicate that it may originate from the coupling between internal motions.