Intramolecular and Intermolecular Contributions to the Barriers for Rotation of Methyl Groups in Crystalline Solids: Electronic Structure Calculations and Solid-State NMR Relaxation Measurements

Wang, Xianlong; Beckmann, Peter A.; Mallory, Clelia W.; Rheingold, Arnold L.; DiPasquale, Antonio G.; Carroll, Patrick J.; Mallory, Frank B.

doi:10.1021/jo2006818

Cited by 26 publications

(53 citation statements)

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“…[34] The differences Vcrystal -ENMR for barriers in the 5 -12 kJ mol -1 range were found to vary from +3 kJ mol -1 to 0.8 kJ mol -1 . For 4,4'-dimethoxybiphenyl, this difference is Vcrystal -ENMR = 1.2 kJ mol -1 .…”

Section: Wang Et Almentioning

confidence: 91%

“…Electronic structure calculations are now able to calculate these relatively small barriers in clusters of molecules with considerable accuracy. [4,34,35] Here we use a central molecule surrounded by 7 whole and 14 half-molecules of 4,4'-dimethoxybiphenyl. This totals more than 300 atoms involving many intermolecular van der Waals interactions as well as intramolecular covalently bonded interactions.…”

Section: Conclusion and Summarymentioning

confidence: 99%

“…Electronic structure calculations provide insights into these rotational motions and Wang et al 3 allow a comparison of the various interactions found in the isolated molecule with those found in a cluster of molecules built from the X-ray diffraction determination of the crystal structure. [4,34,35] Field emission scanning electron microscopy [36] is used to help determine the sizes of the crystallites used in the NMR relaxation experiments. [23] Results Single-crystal X-ray diffraction The crystal structure of 4,4'-dimethoxybiphenyl at 113 K is shown in Figure 2.…”

Section: Introductionmentioning

confidence: 99%

“…[35] The rotational ground state and the rotational transition state identified by this scheme were indistinguishable from those obtained by directly locating the minimum and first-degree saddle points. [34,35] Figure 1(a) shows the optimized ground state structure of the isolated molecule with the parameters as indicated in Table 1. In addition, a two-dimensional potential energy surface as a function of  and  in the isolated molecule was calculated at the B3LYP/6-311+G**//B3LYP/6-311+G** level and is shown in Figure 4.…”

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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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Section: Wang Et Almentioning

confidence: 91%

Section: Conclusion and Summarymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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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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“…The molecule chosen for this study is representative of a large class of compounds that have a variety of rotors with quite different dynamics and as such is a test of the models for methyl and t-butyl group rotation. 2, 3, 5, 6 The novelty of this work is that different sets of neighbouring methyl groups (those attached to the Si atom and those in the t-butyl group) in a relatively complicated molecule in a solid sample have been identified and characterized by their dynamical properties. Readers not interested in the details of the X-ray and solid state NMR relaxation experiments are invited to go directly to the Conclusions.…”

Section: Introductionmentioning

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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Magnetic Interactions through a Nonconjugated Framework Observed in Back‐to‐Back Connected Triazinyl–Nitroxyl Biradical Derivatives

Takahashi

Matsuhashi

Miura

et al. 2018

Chemistry A European J

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Three hetero-biradical derivatives, with the structure of a back-to-back connected benzotriazinyl and tetramethyl or tetraethylisoindoline N-oxyl sharing a common benzo ring, 3-tert-butyl-1-phenyl-1,4,6,8-tetrahydro-6,6,8,8-tetramethyl-pyrrolo[4,5-g]-1,2,4-benzotriazin-4-yl-7-oxyl (1-tBu), 1,3-diphenyl-1,4,6,8-tetrahydro-6,6,8,8-tetramethyl-pyrrolo[4,5-g]-1,2,4-benzotriazin-4-yl-7-oxyl (1-Ph), and 3-tert-butyl-1-phenyl-1,4,6,8-tetrahydro-6,6,8,8-tetraethyl-pyrrolo[4,5-g]-1,2,4-benzotriazin-4-yl-7-oxyl (2-tBu), were synthesized and characterized by single-crystal X-ray analyses, variable-temperature magnetic susceptibility studies, and DFT calculations. Temperature dependences of the magnetic susceptibilities of 1-tBu, 1-Ph, and 2-tBu exhibit broad maxima at 70, 71, and 43 K, respectively. Although these radical derivatives form a columnar or chained assembly in the solid state, magnetic measurements of diluted samples in the polymer matrices and computational results imply that the magnetic properties of the polycrystalline sample can be explained by a two-spin system with an intramolecular antiferromagnetic interaction. The magnetic behavior can be reproduced by using the Bleaney-Bowers model, with 2J=-80.0 cm for 1-tBu, 2J=-77.1 cm for 1-Ph, and 2J=-48.9 cm for 2-tBu. The moderately strong intramolecular antiferromagnetic interactions can be interpreted by a through-bond interaction through the nonconjugated framework and/or through-space interactions based on molecular orbital theory. The strong distance dependency between the N-O spin site and vinylic carbon atoms indicates that the orbital interaction plays an important role in the intramolecular magnetic interaction. The reduced magnetic interaction in 2-tBu relative to those of 1-tBu and 1-Ph can be attributed to restricted rotation of the tetraethyl group.

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Intramolecular and Intermolecular Contributions to the Barriers for Rotation of Methyl Groups in Crystalline Solids: Electronic Structure Calculations and Solid-State NMR Relaxation Measurements

Cited by 26 publications

References 27 publications

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

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

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

Magnetic Interactions through a Nonconjugated Framework Observed in Back‐to‐Back Connected Triazinyl–Nitroxyl Biradical Derivatives

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Intramolecular and Intermolecular Contributions to the Barriers for Rotation of Methyl Groups in Crystalline Solids: Electronic Structure Calculations and Solid-State NMR Relaxation Measurements

Cited by 26 publications

References 27 publications

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

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

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

Magnetic Interactions through a Nonconjugated Framework Observed in Back‐to‐Back Connected Triazinyl–Nitroxyl Biradical Derivatives

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