Quantum tunnelling aspects of methyl group rotation studied by NMR

Horsewill, A.J.

doi:10.1016/s0079-6565(99)00016-3

Cited by 143 publications

(114 citation statements)

References 135 publications

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“…The activation parameters for the two methyl groups are similar and imply that they are relatively hindered [29]. The estimated tunnelling frequency from a potential barrier this size is in the 100s of kHz range, well below the Larmor frequencies involved, justifying the neglect of tunnelling terms to the relaxation [21,35]. This suggests that methyl group "rotation" is a plausible explanation of the 13 C relaxation rates.…”

Section: Methyl Group Dynamicsmentioning

confidence: 75%

“…There have been numerous studies of methyl group rotation probed via proton spinlattice relaxation, incorporating low-temperature regimes and quantum tunnelling effects (reviewed by Horsewill [21]). However, there are relatively few literature precedents for the fitting of 13 C relaxation data more generally in the solid state, particularly in natural abundance samples.…”

Section: C Spin-lattice Relaxation Times In Solidsmentioning

confidence: 99%

“…Fitting to such expressions involves a number of assumptions. Firstly, that quantum tunnelling effects can be ignored [21,29], which is justified here by the relatively high barriers to motion that are determined below. Secondly, that an expression that is valid for molecules tumbling in isotropic solution is also valid for powder samples under magic-angle spinning [23,30].…”

Section: C Spin-lattice Relaxation Times In Solidsmentioning

confidence: 99%

“…which is a good approximation for the limited temperature range observed [21]. The error bars from the fitting of the T 1 values, as shown in Figure 4, were used to weight the data points in the calculation of χ 2 during the fitting of the temperature dependence.…”

Section: Methyl Group Dynamicsmentioning

confidence: 99%

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NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

Apperley

Markwell

Frantsuzov

et al. 2013

Phys. Chem. Chem. Phys.

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Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT Solid-state NMR is used to characterise dynamics in the ethanol solvate of the pharmaceutical material formoterol fumarate and its associated desolvate. Jump rates and activation barriers for dynamic processes such as phenyl ring rotation and methyl group rotational diffusion are derived from 1D-EXSY and 13 C spin-lattice relaxation times respectively. 2 H and 13 C spin-lattice relaxation times measured under magic-angle spinning conditions are used to show that the fumarate ion in the desolvate is undergoing smallamplitude motion on a frequency scale of 100s of MHz at ambient temperature with an activation parameter of about 32 kJ mol -1 . Exact calculations of relaxation times under MAS provide a simple and robust means to test motional models in cases where relaxation rate maxima are observed, including for systems where the crystal structure of the material is unknown.

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Section: Methyl Group Dynamicsmentioning

confidence: 75%

Section: C Spin-lattice Relaxation Times In Solidsmentioning

confidence: 99%

Section: C Spin-lattice Relaxation Times In Solidsmentioning

confidence: 99%

Section: Methyl Group Dynamicsmentioning

confidence: 99%

See 2 more Smart Citations

NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

Apperley

Markwell

Frantsuzov

et al. 2013

Phys. Chem. Chem. Phys.

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“…31 We first consider just the methyl groups bonded to the Si atom. The rotation axes of these methyl groups are not moving on the NMR time scale.…”

Section: Resultsmentioning

confidence: 99%

Methyl and t-butyl group rotation in a molecular solid:¹H NMR spin-lattice relaxation and X-ray diffraction

Beckmann

Moore

Rheingold

2016

Phys. Chem. Chem. Phys.

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Methyl and t-butyl group rotation in a molecular solid: 1H NMR spin-lattice relaxation and X-ray diffraction. P A Beckmann, C E Moore, and A L Rheingold 2016 Physical Chemistry Chemical Physics, 18 1720-1726. Methyl and t-butyl AbstractWe report solid state 1 H nuclear magnetic resonance spin-lattice relaxation experiments and X-ray diffractometry in 2-t-butyldimethylsilyloxy-6-bromonaphthalene. This compound offers an opportunity to simultaneously investigate, and differentiate between, the rotations of a t-butyl group [C(CH 3 ) 3 ] and its three constituent methyl groups (CH 3 ) and, simultaneously, a pair of 'lone' methyl groups (attached to the Si atom). The solid state 1 H relaxation experiments determine activation energies for these rotations. We review the models for the dynamics of both 'lone' methyl groups (ones whose rotation axes do not move on the NMR time scale) and models for the dynamics of the t-butyl group and its constituent methyl groups (whose rotation axes reorient on the NMR time scale as the t-butyl group rotates).

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Stereochemical Nonrigidity of Organometallic Complexes

Faller¹

2005

Encyclopedia of Inorganic Chemistry

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Compounds that undergo intramolecular rearrangements at rates that affect the NMR line shapes in generally accessible temperature ranges are described as stereochemically nonrigid. Analysis of 1D and 2D NMR spectra as a function of temperature often allow the rates, as well as the mechanisms of interconversion of conformers or isomers, to be determined. Examples were selected to illustrate the importance of stereochemical nonrigidity in reactivity and the potential for affecting stereochemistry in the products of reactions.

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Quantum tunnelling aspects of methyl group rotation studied by NMR

Cited by 143 publications

References 135 publications

NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

Methyl and t-butyl group rotation in a molecular solid:¹H NMR spin-lattice relaxation and X-ray diffraction

Stereochemical Nonrigidity of Organometallic Complexes

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Quantum tunnelling aspects of methyl group rotation studied by NMR

Cited by 143 publications

References 135 publications

NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

Methyl and t-butyl group rotation in a molecular solid:1H NMR spin-lattice relaxation and X-ray diffraction

Stereochemical Nonrigidity of Organometallic Complexes

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Product

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Methyl and t-butyl group rotation in a molecular solid:¹H NMR spin-lattice relaxation and X-ray diffraction