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  Reorientational tunneling of partially deuterated methyl groups: A single-crystal deuteron NMR study of aspirin-CH2D

Detken, A., & Zimmermann, H. (1998). Reorientational tunneling of partially deuterated methyl groups: A single-crystal deuteron NMR study of aspirin-CH2D. The Journal of Chemical Physics, 108(14), 5845-5854. doi:10.1063/1.475995.

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Genre: Journal Article
Alternative Title : Reorientational tunneling of partially deuterated methyl groups: A single-crystal deuteron NMR study of aspirin-CH2D

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JChemPhys_108_1998_8550.pdf (Any fulltext), 147KB
 
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 Creators:
Detken, Andreas1, Author           
Zimmermann, Herbert2, 3, Author           
Affiliations:
1Emeritus Group Bioorganic Chemistry, Max Planck Institute for Medical Research, Max Planck Society, ou_1497711              
2Department of Molecular Physics, Max Planck Institute for Medical Research, Max Planck Society, ou_1497705              
3Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society, ou_1497700              

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 Abstract: Partially deuterated methyl groups in single crystals of aspirin are investigated by deuteron NMR at temperatures between 8 K and room temperature. The CH2D groups perform reorientations which are governed by a rotational potential with three wells, two of which are almost equally deep whereas the third is significantly deeper. At temperatures below 20 K, a so far unobserved type of incoherent tunneling process is identified. This process consists in reorientations between the two upper potential wells which are fast on the time scale of the quadrupolar interaction, whereas transitions into the deeper well are slow on this time scale. At temperatures above 35 K, the methyl groups perform thermally activated stochastic reorientations between all three potential wells. By determining the relative populations of the three wells as a function of temperature, the energy difference between the lower and the two upper wells is found to be 3.3 meV. This amounts to almost 8% of the average barrier height, which is determined from the temperature dependence of the spin-lattice relaxation time to be 43 meV.

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Language(s): eng - English
 Dates: 1997-12-011998-01-081998-04-08
 Publication Status: Issued
 Pages: 10
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
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Title: The Journal of Chemical Physics
  Other : J. Chem. Phys.
Source Genre: Journal
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Publ. Info: Woodbury, N.Y. : American Institute of Physics
Pages: - Volume / Issue: 108 (14) Sequence Number: - Start / End Page: 5845 - 5854 Identifier: ISSN: 0021-9606
CoNE: https://pure.mpg.de/cone/journals/resource/954922836226