Measured and calculated rotational tunnelling dynamics in methyl acetate

Neumann, Marcus A.; Johnson, Mark R.; Aibout, A.; Horsewill, A.J.

doi:10.1016/s0301-0104(98)00039-1

Cited by 11 publications

(4 citation statements)

References 17 publications

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“…Systematic studies of barrier heights and tunneling frequencies of CH 3 groups in the series CH 3 −(CH 3 ) n −CO−(CH 2 ) m −CH 3 have shown that methyl groups next to carboxyl groups have low barrier heights . Thus, it may be that in NMA the tunneling lines are as low in energy as those in 2-butadone, methyl acetate, and acetanilide observed up to 0.8 μeV, but unfortunately are resolution-limited in this experiment. As a result, as shown in Figure , below 100 K the tunneling motion would dominate but be resolution limited, while above 100 K, once the structure of the tunneling lines has disappeared, the rotational motion of the methyl groups would become more important.…”

Section: Resultsmentioning

confidence: 61%

“…There is strong evidence for the existence of a universal law for methyl dynamics, suggesting that tunneling frequency depends exponentially on the height of the rotation barrier. Systematic studies of barrier heights and tunneling frequencies of CH 3 groups in the series CH 3 -(CH 3 ) n -CO-(CH 2 ) m -CH 3 have shown that methyl groups next to carboxyl groups have low barrier heights.34 Thus, it may be that in NMA the tunneling lines are as low in energy as those in 2-butadone, 34 methyl acetate,35 and acetanilide36 observed up to 0.8 µeV, but unfortunately are resolution-limited in this experiment. As a result, as shown in Figure…”

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confidence: 99%

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Hydrogen inN-Methylacetamide: Positions and Dynamics of the Hydrogen Atoms Using Neutron Scattering

et al. 2007

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This work reports neutron diffraction and incoherent neutron scattering experiments on N-methylacetamide (NMA), which can be considered the model building block for the peptide linkage of polypeptides and proteins. Using the neutron data, we have been able to associate the onset of a striking negative thermal expansion (NTE) along the a-axis with a dynamical transition around 230 K, consistent with our calorimetric experiments. Observation of the NTE raises the question of possible proton transfer in NMA, which, from our data alone, still cannot be settled. We can only speculate that intermolecular repulsive forces increase as the O...H distance decreases upon cooling, and that around 230 K the lattice relaxes without observation of an actual proton transfer. However, the existence of a nonharmonic potential, reflected by the behavior of the phonon vibrations together with the observation of NTE, could be justified by the "vibrational" polaron theory in which a dynamic localization of the vibrational energy is created by coupling an internal molecular mode to a lattice phonon. More generally, this work shows that neutron powder diffraction techniques can be very powerful for investigating structural deformations in small peptide systems.

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Section: Resultsmentioning

confidence: 61%

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confidence: 99%

Hydrogen inN-Methylacetamide: Positions and Dynamics of the Hydrogen Atoms Using Neutron Scattering

et al. 2007

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“…These sidebands involve simultaneous changes in tunnelling and 1 H spin states and therefore provide the opportunity to study the mechanisms of driving A-E transitions by rf irradiation. The experiment can be conducted either by sweeping the B-field at constant m rf [6,[8][9][10] or by sweeping m rf at constant B-field [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Methyl tunnelling sidebands in the low-field NMR spectrum of 3-pentanone: Driving A–E transitions using rf irradiation

Zhang

Horsewill

2015

Journal of Magnetic Resonance

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“…However, the method favored in this work is based on an eigenstateby-eigenstate search using the variational principle (14), which can be applied to systems of very high dimension, as are typically encountered, for example, in quantum chemistry methods (15). A one-dimensional mean-field solution of H can also be obtained that describes the effective potential due to delocalization of neighboring methyl groups (16).…”

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confidence: 99%

Quantitative Atom-Atom Potentials from Rotational Tunneling: Their Extraction and Their Use

Johnson

Kearley

2000

Annu. Rev. Phys. Chem.

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Key Words tunneling, force fields, quantum chemistry, neutron scattering s Abstract Rotational tunneling of small molecular groups has been the subject of considerable theoretical and experimental activity for several decades. Much of this activity has been driven by the promise of exploiting the extreme sensitivity of quantum tunneling to interatomic potentials, but until recently, there was no straightforward means by which quantitative information about these potentials could be extracted. This review explains how a quantitative method, suitable for general application, was developed. It then goes on to show how this has been used to understand tunneling systems for which no previous satisfactory explanation had been found. The application of the methodology, and its results, to other disciplines is discussed.

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Measured and calculated rotational tunnelling dynamics in methyl acetate

Cited by 11 publications

References 17 publications

Hydrogen inN-Methylacetamide: Positions and Dynamics of the Hydrogen Atoms Using Neutron Scattering

Hydrogen inN-Methylacetamide: Positions and Dynamics of the Hydrogen Atoms Using Neutron Scattering

Methyl tunnelling sidebands in the low-field NMR spectrum of 3-pentanone: Driving A–E transitions using rf irradiation

Quantitative Atom-Atom Potentials from Rotational Tunneling: Their Extraction and Their Use

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