Methyl tunnelling, reorientation and NMR relaxation in solid acetates.
Rotational excitations of methyl groups in six solid acetates have been investigated by 1H nuclear magnetic resonance (NMR) relaxation time measurements at 15 MHz and 30 MHz and at temperatures between 10 K and the melting point. Hindering barriers between 1.6 kJ/mol and 3.7 kJ/mol have been found that could be correlated to the tunnelling frequencies observed by inelastic neutron scattering. A consistent description of the relaxation rate dependences from the classical regime at high temperatures to the quantum-mechanical regime at low temperatures is possible by Haupt's equation. The rotational potentials are mainly determined by inter-molecular interaction with an important influence of water of crystallization, if present.
Kuhnen
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Institut für Physikalische Chemie, der Westfälischen Wilhelms-Universität, Münster, Germany.
Vermathen
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Müller-Warmuth
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D000085:Acetates / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008432:Mathematical Computing; D008968:Molecular Conformation; D013696:Temperature
D000085:Acetates