The shape and information content of high-field solid-state proton NMR spectra of methyl groups

Gutsche, Peter; Rinsdorf, Monika; Zimmermann, Herbert; Schmitt, H.; Haeberlen, Ulrich

doi:10.1016/s0926-2040(03)00061-4

Cited by 12 publications

(21 citation statements)

References 33 publications

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“…As is well known, 41 in the instances of low torsional barriers even if the incoherent dynamics can be frozen at low temperatures, large coherent tunnelling effects appearing at such temperatures affect the spectral patterns in almost the same way as rapid incoherent processes do at elevated temperatures.…”

Section: Discussionmentioning

confidence: 85%

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A quantum mechanical alternative to the Arrhenius equation in the interpretation of proton spin–lattice relaxation data for the methyl groups in solids

Bernatowicz

Shkurenko

Osior

et al. 2015

Phys. Chem. Chem. Phys.

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CitationQuantum mechanical alternative to Arrhenius equation in the interpretation of proton spin-lattice relaxation data for the methyl groups in solids 2015 Phys. Chem. Chem. Phys. Theory of nuclear spin-lattice relaxation in methyl groups in solids has been a recurring problem in nuclear magnetic resonance (NMR) spectroscopy. The current view is that, except for extreme cases of low torsional barriers where special quantum effects are at stake, the relaxation behaviour of the nuclear spins in methyl groups is controlled by thermally activated classical jumps of the methyl group between its three orientations. The temperature effects on the relaxation rates can be modelled by Arrhenius behaviour of the correlation time of the jump process. The entire variety of relaxation effects in protonated methyl groups has recently been given a consistently quantum mechanical explanation not invoking the jump model regardless of the temperature range. It exploits the damped quantum rotation (DQR) theory originally developed to describe NMR line shape effects for hindered methyl groups. In the DQR model, the incoherent dynamics of the methyl group include two quantum rate, i.e., coherence-damping processes. For proton relaxation only one of these processes is relevant. In this paper, temperature-dependent proton spin-lattice relaxation data for the methyl groups in polycrystalline methyltriphenyl silane and methyltriphenyl germanium, both deuterated in aromatic positions, are reported and interpreted in terms of the DQR model. A comparison with the conventional approach exploiting the phenomenological Arrhenius equation is made. The present observations provide further indications that incoherent motions of molecular moieties in condensed phase can retain quantum character over much broader temperature range than is commonly thought. Eprint version

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Section: Discussionmentioning

confidence: 85%

“…The relaxation and line shape investigations involved a single crystal of selectively deuterated methylmalonic acid in a fixed orientation in the external magnetic field. 41 . The Arrhenius trend obtained from the relaxation data have proved to exactly continue the temperature trend of k t extracted in the DQR line shape fits using Eq.…”

Section: Discussionmentioning

confidence: 99%

A quantum mechanical alternative to the Arrhenius equation in the interpretation of proton spin–lattice relaxation data for the methyl groups in solids

Bernatowicz

Shkurenko

Osior

et al. 2015

Phys. Chem. Chem. Phys.

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“…Molecular libration has to be respected since even the line splitting of the methylene group of acetonitrile trapped in an organic crystal at T = 216 K significantly deviates from the value of 3D 0 = 63.9 kHz which is expected in the case of freezing of any type of motion [11]. For adapting this relation to methyl groups in cytosolic metabolites in vivo we assume that the C-R axis undergoes a tumbling motion similar to that of the internuclear vector between the protons of the CH 2 group.…”

Section: Theorymentioning

confidence: 99%

Molecular dynamics and information on possible sites of interaction of intramyocellular metabolites in vivo from resolved dipolar couplings in localized 1H NMR spectra

Schröder

Schmitz

Bachert

2004

Journal of Magnetic Resonance

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“…Because the former have threefold symmetry, they render the symmetry-violating parts of the latter ineffective in consequence of which the observed spectral multiplet undergoes a considerable simplification. 5,6 With increasing temperature, the coherent tunneling will be progressively dominated by thermally activated incoherent dynamics which ultimately prevail. In the high temperature limit, the spectral pattern of a protonated rotator approaches essentially the same form as it would have at low temperatures if the Heisenberg couplings were large against the DD and CSA interactions.…”

Section: Introductionmentioning

confidence: 99%

“…For low torsional barriers, below, say, 2.5 kcal mol 1 , such a simple form, compatible with the threefold symmetry, is maintained by the spectral pattern over the whole temperature range, with no detectable lineshape effects at the intermediate temperatures. 5,6 For protonated rotators, the impact on the spectral line shapes of the incoherent processes 0021-9606/2017/146(10)/104504/11/$30.00…”

Section: Introductionmentioning

confidence: 99%

Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder 1H NMR spectra

Osior

Kalicki

Kamieński

et al. 2017

The Journal of Chemical Physics

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According to the damped quantum rotation (DQR) theory, hindered rotation of methyl groups, evidenced in nuclear magnetic resonance (NMR) line shapes, is a nonclassical process. It comprises a number of quantum-rate processes measured by two different quantum-rate constants. The classical jump model employing only one rate constant is reproduced if these quantum constants happen to be equal. The values of their ratio, or the nonclassicallity coefficient, determined hitherto from NMR spectra of single crystals and solutions range from about 1.20 to 1.30 in the latter case to above 5.0 in the former, with the value of 1 corresponding to the jump model. Presently, first systematic investigations of the DQR effects in wide-line NMR spectra of a powder sample are reported. For 1,1,1-triphenylethane deuterated in the aromatic positions, the relevant line-shape effects were monitored in the range 99-121 K. The values of the nonclassicality coefficient dropping from 2.7 to 1.7 were evaluated in line shape fits to the experimental powder spectra from the range 99-108 K. At these temperatures, the fits with the conventional line-shape model are visibly inferior to the DQR fits. Using a theoretical model reported earlier, a semiquantitative interpretation of the DQR parameters evaluated from the spectra is given. It is shown that the DQR effects as such can be detected in wide-line NMR spectra of powdered samples, which are relatively facile to measure. However, a fully quantitative picture of these effects can only be obtained from the much more demanding experiments on single crystals.

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The shape and information content of high-field solid-state proton NMR spectra of methyl groups

Cited by 12 publications

References 33 publications

A quantum mechanical alternative to the Arrhenius equation in the interpretation of proton spin–lattice relaxation data for the methyl groups in solids

A quantum mechanical alternative to the Arrhenius equation in the interpretation of proton spin–lattice relaxation data for the methyl groups in solids

Molecular dynamics and information on possible sites of interaction of intramyocellular metabolites in vivo from resolved dipolar couplings in localized 1H NMR spectra

Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder 1H NMR spectra

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