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Anomalous proton relaxation, rotational tunnelling and barriers to methyl group rotation in solid acetyl halides

Solid State Nuclear Magnetic Resonance, ISSN: 0926-2040, Vol: 4, Issue: 3, Page: 153-161
1995
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Metric Options:   Counts1 Year3 Year

Metrics Details

  • Citations
    22
    • Citation Indexes
      22
  • Captures
    2

Article Description

Rotational excitations of methyl groups attached to carbonyl in solid acetic acid, acetyl fluoride, acetyl chloride and acetyl bromide have been investigated by 1 H nuclear magnetic resonance (NMR) relaxation times and field-cycling measurements at two frequencies and various temperatures. The tunnel splittings have been found to occur between 3.3 and 0.08 μeV making quantum effects important for the relaxation behaviour. For the acetyl halides, similar tunnelling and NMR frequencies lead to an anomalous-looking temperature dependence of the relaxation rates. A consistent description by Haupt's equation is possible. The rotational potentials have been derived from the data and compared with those obtained from microwave spectra of the corresponding isolated molecules. The hindering potential is purely three-fold and the barrier is dominated by the functional group.

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