Methyl group rotation, 1H spin-lattice relaxation in an organic solid, and the analysis of nonexponential relaxation

Beckmann, Peter A.; Schneider, Evan

doi:10.1063/1.3677183

Cited by 30 publications

(96 citation statements)

References 94 publications

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“…The rotation axes of these methyl groups are not moving on the NMR time scale. The initial relaxation rate R S of a perturbed 1 H magnetization is 9,[32][33][34] …”

Section: Resultsmentioning

confidence: 99%

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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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“…The rotation axes of these methyl groups are not moving on the NMR time scale. The initial relaxation rate R S of a perturbed 1 H magnetization is 9,[32][33][34] …”

Section: Resultsmentioning

confidence: 99%

“…It was deemed exponential above these temperatures (i.e., β > 0.95). When the relaxation was nonexponential, the initial (short time) slope of the perturbed magnetization was determined (as outlined elsewhere 9 ) and this parameter, discussed further in the Results section, is called R S .…”

Section: Nmr Spin-lattice Relaxationmentioning

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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“…When methyl group rotation is responsible for the relaxation, the relaxation is nonexponential near the maximum in the relaxation rate and at higher temperatures [2,[8][9][10][22][23][24][25][26][27][28]. The recovery of the perturbed magnetization M(0) at these higher temperatures can be fitted by a stretched exponential;…”

Section: A Review Of the 1 H Spin-lattice Relaxation Modelmentioning

confidence: 99%

“…where R* is the characteristic relaxation rate and β is the stretching parameter [11,22,[29][30][31][32][33][34][35]. If the relaxation is exponential to within experimental uncertainty, β = 1 and R* is labeled R. This occurs in pure compounds like 1 and 2 at temperatures below the maximum in the relaxation rate [2,[8][9][10][22][23][24][25][26][27][28].…”

Section: A Review Of the 1 H Spin-lattice Relaxation Modelmentioning

confidence: 99%

“…If the relaxation is exponential to within experimental uncertainty, β = 1 and R* is labeled R. This occurs in pure compounds like 1 and 2 at temperatures below the maximum in the relaxation rate [2,[8][9][10][22][23][24][25][26][27][28]. R* and β are not amenable to interpretation in any closed-form model and we use β solely as an indicator of the degree of nonexponentiality.…”

Section: A Review Of the 1 H Spin-lattice Relaxation Modelmentioning

confidence: 99%

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Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation

Beckmann

Bohen

Ford

et al. 2017

Solid State Nuclear Magnetic Resonance

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experiments allow us to observe the temperature dependence of the parameters that characterize methyl group rotation in both compounds and in mixtures of the two compounds. In the mixtures, both types of methyl groups (that is, molecules of 1 and 2) can be observed independently and simultaneously at low temperatures because the solid state 1 H spin-lattice relaxation is appropriately described by a double exponential. We have followed the conversion 1 → 2 over periods of two years. The solid state 1 H spin-lattice relaxation experiments in pure samples of 1 and 2 indicate that there is a distribution of NMR activation energies for methyl group rotation in 1 but not in 2 and we are able to explain this in terms of the particle sizes seen in the field emission scanning electron microscopy images.

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Single‐Crystal X‐Ray Diffraction, Isolated‐Molecule and Cluster Electronic Structure Calculations, and Scanning Electron Microscopy in an Organic solid: Models for Intramolecular Motion in 4,4′‐Dimethoxybiphenyl

Wang

Rotkina

et al. 2012

ChemPhysChem

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Single-crystal X-ray diffraction, isolated-molecule and cluster electronic structure calculations, and scanning electron microscopy in an organic solid: Models for intramolecular motion in 4,4'-dimethoxybiphenyl http://onlinelibrary.wiley.com/doi/10.1002/cphc.201101067/abstract Xianlong Wang, *[a] Lolita Rotkina, [b] Hong Su, [c] and Peter A. Beckmann, Mawr, Pennsylvania 19010-2899, USA Fax: (+1) 610-526-7489 E-mail: pbeckman@brynmawr.edu Accepted for publication in ChemPhysChem February 2012This paper brings together field emission scanning electron microscopy, single-crystal Xray diffraction, and ab initio electronic structure calculations in both an isolated molecule and a cluster of 7 whole and 14 half molecules of 4,4'-dimethoxybiphenyl to investigate coupled methyl group rotation (over a barrier) and methoxy group libration (meaning a rotation from the ground state not all the way to the transition state and back again). The structure of the isolated molecule, determined by the electronic structure calculations, is compared with the structure of the molecule found in the crystal. As the methyl group rotates from its ground state to its transition state, the methoxy group rotates 30 O in the isolated molecule and 16 O in the cluster. The calculated barriers for this coupled methyl group rotation and methoxy group libration in the isolated molecule and in the crystal are 12.8 kJ mol -1 and 10.3 kJ mol -1 respectively, suggesting that intermolecular interactions in the crystal lower the barrier. These barriers are compared with the value of 11.5 ± 0.5 kJ mol -1 obtained from solid state 1 H spin-lattice relaxation measurements [P. A. Beckmann and E. Schneider, J. Chem. Phys. 2012, 136, 054508, 1-9.] Wang et al 2 IntroductionSmall methyl-substituted organic molecules in the solid state are good systems for investigating (1) the relationship between methyl group rotation and molecular and crystal structure [1][2][3][4][5][6][7][8][9][10][11][12] and (2) for developing models for intramolecular motion. [7,11,[13][14][15][16] They are also good test cases for comparing calculated and measured barriers to intramolecular motion. [17][18][19][20][21][22] In this paper we bring together single crystal X-ray crystallography, isolated molecule and molecular cluster ab initio electronic structure calculations, and field emission scanning electron microscopy with 4,4'-dimethoxybiphenyl (Figures 1 and 2). This allows us to relate the properties describing methyl group rotation and methoxy group libration to the structure on both the microscopic and macroscopic scales. By "methyl group rotation", we mean a rotation from a ground state to a transition state followed by a return to the ground state either by rotating in the same direction or by rotating in the opposite direction. By "methoxy group libration", we mean a rotation from the ground state only part way to the transition state followed by a reversal of the rotation back to the ground state. We compare the calculated barrier for this coupled met...

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Methyl group rotation, 1H spin-lattice relaxation in an organic solid, and the analysis of nonexponential relaxation

Cited by 30 publications

References 94 publications

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

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

Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation

Single‐Crystal X‐Ray Diffraction, Isolated‐Molecule and Cluster Electronic Structure Calculations, and Scanning Electron Microscopy in an Organic solid: Models for Intramolecular Motion in 4,4′‐Dimethoxybiphenyl

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Methyl group rotation, 1H spin-lattice relaxation in an organic solid, and the analysis of nonexponential relaxation

Cited by 30 publications

References 94 publications

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

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

Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation

Single‐Crystal X‐Ray Diffraction, Isolated‐Molecule and Cluster Electronic Structure Calculations, and Scanning Electron Microscopy in an Organic solid: Models for Intramolecular Motion in 4,4′‐Dimethoxybiphenyl

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

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