Methyl and t-butyl reorientation in an organic molecular solid

Beckmann, Peter A.; Dougherty, William G.; Kassel, W. Scott

doi:10.1016/j.ssnmr.2009.06.002

Cited by 8 publications

(21 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The relaxation rate R is given by [4] a sum of several terms of the form R = E i tend to be determined with reasonable accuracy by the experiment (± 10%). They should fall within well-defined norms for the kinds of motions being studied here [3,5,7,8].…”

Section: The Spin-lattice Relaxation Model and The Nmr Fitting Paramementioning

confidence: 84%

“…The previous studies either had no additional "lone" methyl groups [3,5,6] or the relaxation rate from the rotation of the lone methyl groups was observed in the temperature range studied [4].…”

Section: The Spin-lattice Relaxation Model and The Nmr Fitting Paramementioning

confidence: 88%

“…R values were measured using an inversion-recovery pulse sequence. Further details of the measurement process and temperature control and measurement are provided elsewhere [4]. There were no thermal history effects.…”

Section: The Experimentsmentioning

confidence: 99%

“…In this model, the in-plane methyl group reorients at the same rate as the t-butyl group, whereas the two out-of-plane methyl groups usually reorient more rapidly. This model is easily extended [4] to systems like that studied here (5-t-butyl-4-hydroxy-2-methylphenyl sulfide [the sulfide]; see Fig. 1) which have both t-butyl groups and "lone" methyl groups (meaning methyl groups not in t-butyl groups; in this case the 2-methyl groups).…”

Section: Introductionmentioning

confidence: 99%

“…1) which have both t-butyl groups and "lone" methyl groups (meaning methyl groups not in t-butyl groups; in this case the 2-methyl groups). In a recent study we tested the model with 4,5-dibromo-2,7-di-t-butyl-9,9-dimethylxanthene (the xanthene) where the lone methyl groups (the 9-methyl groups) were found to have rotational barriers similar to the rotational barriers of the out-of-plane methyl groups in the t-butyl groups [4]. It was concluded that the rotation of the lone methyl groups was clearly discernable in the high-temperature, thermally assisted hopping regime studied, even though the relaxation rate for this lone methyl group motion occurred in the same temperature region as the relaxation rate resulting from the motion of the out-of-plane methyl groups in the t-butyl groups, as could be predicted by the structure of the xanthene molecule.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state

Popa

Rheingold

Beckmann

2010

Solid State Nuclear Magnetic Resonance

Self Cite

View full text Add to dashboard Cite

We have measured the solid state nuclear magnetic resonance (NMR) 1 H spin-lattice relaxation rate from 93 to 340 K at NMR frequencies of 8.5 and 53 MHz in 5-t-butyl-4-hydroxy-2-methylphenyl sulfide. We have also determined the molecular and crystal structure from X-ray diffraction experiments. The relaxation is caused by methyl and t-butyl group rotation modulating the spin-spin interactions and we relate the NMR dynamical parameters to the structure. A successful fit of the data requires that the 2-methyl groups are rotating fast (on the NMR time scale) even at the lowest temperatures employed. The rotational barrier for the two out-of-plane methyl groups in the t-butyl groups is 14.3 ± 2.7 kJ mol -1 and the rotational barrier for the t-butyl groups and their in-plane methyl groups is 24.0 ± 4.6 kJ mol -1 . The uncertainties account for the uncertainties associated with the relationship between the observed NMR activation energy and a model-independent barrier, as well as the experimental uncertainties.

show abstract

Section: The Spin-lattice Relaxation Model and The Nmr Fitting Paramementioning

confidence: 84%

Section: The Spin-lattice Relaxation Model and The Nmr Fitting Paramementioning

confidence: 88%

Section: The Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state

Popa

Rheingold

Beckmann

2010

Solid State Nuclear Magnetic Resonance

Self Cite

View full text Add to dashboard Cite

show abstract

Hydrogen‐Bonded Crystalline Molecular Machines with Ultrafast Rotation and Displacive Phase Transitions

Colin‐Molina

Jellen

Rodríguez‐Hernández

et al. 2020

Chemistry A European J

View full text Add to dashboard Cite

Two new crystalline rotors 1 and 2 assembled through N−H⋅⋅⋅N hydrogen bonds by using halogenated carbazole as stators and 1,4‐diaza[2.2.2]bicyclooctane (DABCO) as the rotator, are described. The dynamic characterization through 1H T1 relaxometry experiments indicate very low rotational activation barriers (Ea) of 0.67 kcal mol−1 for 1 and 0.26 kcal mol−1 for 2, indicating that DABCO can reach a THz frequency at room temperature in the latter. These Ea values are supported by solid‐state density functional theory computations. Interestingly, both supramolecular rotors show a phase transition between 298 and 250 K, revealed by differential scanning calorimetry and single‐crystal X‐ray diffraction. The subtle changes in the crystalline environment of these rotors that can alter the motion of an almost barrierless DABCO are discussed here.

show abstract

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

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Methyl and t-butyl reorientation in an organic molecular solid

Cited by 8 publications

References 13 publications

A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state

A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state

Hydrogen‐Bonded Crystalline Molecular Machines with Ultrafast Rotation and Displacive Phase Transitions

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

Contact Info

Product

Resources

About