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C-13 NMR of tunnelling methyl groups

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons92644

Detken,  Andreas
Emeritus Group Bioorganic Chemistry, Max Planck Institute for Medical Research, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons128263

Zimmermann,  Herbert
Department of Molecular Physics, Max Planck Institute for Medical Research, Max Planck Society;
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons93258

Haeberlen,  Ulrich
Research Group Prof. Dr. Haeberlen, Max Planck Institute for Medical Research, Max Planck Society;

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Zitation

Detken, A., Zimmermann, H., & Haeberlen, U. (1999). C-13 NMR of tunnelling methyl groups. Molecular Physics, 96(6), 927-940. doi:10.1080/002689799165035.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0024-A6B3-9
Zusammenfassung
The dipolar interactions between the protons and the central 13C nucleus of a 13CH3 group are used to study rotational tunnelling and incoherent dynamics of such groups in molecular solids. Single-crystal 13C NMR spectra are derived for arbitrary values of the tunnel frequency upsilon t. Similarities to ESR and 2H NMR are pointed out. The method is applied to three different materials. In the hydroquinone/acetonitrile clathrate, the unique features in the 13C NMR spectra which arise from tunnelling with a tunnel frequency that is much larger than the dipolar coupling between the methyl protons and the 13C nucleus are demonstrated, and the effects of incoherent dynamics are studied. The broadening of the 13C resonances is related to the width of the quasi-elastic line in neutron scattering. Selective magnetization transfer experiments for studying slow incoherent dynamics are proposed. For the strongly hindered methyl groups of L-alanine, an upper limit for upsilon is derived from the 13C NMR spectrum. In aspirinTM (acetylsalicylic acid), incoherent reorientations dominate the spectra down to the lowest temperatures studied; their rate apparently increases with decreasing temperature below 25K