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Methyl tunnelling, reorientation and NMR relaxation in solid acetates
A Kuhnen1, P Vermathen, W Müller-Warmuth
1Institut für Physikalische Chemie, der Westfälischen Wilhelms-Universität, Münster, Germany.
Solid State Nuclear Magnetic Resonance
|April 29, 1998
Summary
Investigating methyl group rotations in solid acetates using 1H NMR relaxation reveals hindering barriers. These barriers correlate with quantum tunneling, explained by Haupt
Area of Science:
- Solid-state chemistry
- Materials science
- Physical chemistry
Background:
- Methyl groups in solid acetates exhibit rotational dynamics.
- Understanding these dynamics is crucial for material properties.
Purpose of the Study:
- To investigate rotational excitations of methyl groups in six solid acetates.
- To determine hindering barriers and their correlation with quantum tunneling.
Main Methods:
- 1H nuclear magnetic resonance (NMR) relaxation time measurements at 15 MHz and 30 MHz.
- Temperature range: 10 K to melting point.
Main Results:
- Hindering barriers between 1.6 kJ/mol and 3.7 kJ/mol were identified.
- Barriers correlate with tunneling frequencies from inelastic neutron scattering.
- Haupt's equation consistently describes relaxation rates across temperature regimes.
Conclusions:
- Rotational potentials are primarily governed by intermolecular interactions.
- Water of crystallization significantly influences rotational potentials.