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           nuclear magnetic resonance spin-lattice relaxation, C13 magic-angle-spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and x-ray diffraction of two polymorphs of 2,6-di-<i>tert</i>-butylnaphthalene

Beckmann, Peter A.; Burbank, Kendra S.; Clemo, Katharine M.; Slonaker, Erin N.; Averill, Kristin; Dybowski, Cecil; Figueroa, Joshua S.; Glatfelter, Alicia; Koch, S.; Liable‐Sands, Louise M.; Rheingold, Arnold L.

doi:10.1063/1.482000

Cited by 31 publications

(46 citation statements)

References 11 publications

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“…26 Very small differences in H-H separations, r, have a huge effect since the interactions that enter the expressions for the observed relaxation rates are proportional to r −6 . There are cases where different polymorphs have very different observed R versus T −1 curves 29,30 and there are cases, such as that observed here and elsewhere, 15,92 where small changes in the observed R versus T −1 curves have yet to be correlated with different structures determined from x-ray diffraction. 1 H NMR relaxation in the solid state is probably much more sensitive to small structural changes than either neutron scattering or x-ray diffraction.…”

Section: Conclusion and Summarymentioning

confidence: 85%

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

Beckmann

Schneider

2012

The Journal of Chemical Physics

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We report 1 H spin-lattice relaxation measurements in polycrystalline 4,4 -dimethoxybiphenyl at temperatures between 80 and 300 K at NMR frequencies of ω 0 /2π = 8.50, 22.5, and 53.0 MHz. The data are interpreted in terms of the simplest possible Bloch-Wangsness-Redfield methyl group hopping model. Different solid states are observed at low temperatures. The 1 H spin-lattice relaxation is nonexponential at higher temperatures where a stretched-exponential function fits the data very well, but this approach is phenomenological and not amenable to theoretical interpretation. (We provide a brief literature review of the stretched-exponential function.) The Bloch-Wangsness-Redfield model applies only to the relaxation rate that characterizes the initial 1 H magnetization decay in a high-temperature nonexponential 1 H spin-lattice relaxation measurement. A detailed procedure for determining this initial relaxation rate is described since large systematic errors can result if this is not done carefully.

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Section: Conclusion and Summarymentioning

confidence: 85%

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

Beckmann

Schneider

2012

The Journal of Chemical Physics

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“…The molecular structure in this class of compounds, as determined by X-ray diffraction experiments, show the t-butyl groups oriented such that one methyl group is in the aromatic plane, or nearly so, and two methyl groups are out of the plane [1]. The in-plane methyl group reorients at the same rate as the t-butyl group, whereas the two out-ofplane methyl groups usually reorient more rapidly, though in some cases, like that reported here, a very simple model can be used whereby all four rotors reorient at the Methyl and t-butyl reorientation in an organic molecular solid 3 same rate [2]. An important aspect of the mathematical models used to interpret the observed spin-lattice relaxation rates is that the number of rotors reorienting on the NMR time scale are properly accounted for.…”

Section: Introductionmentioning

confidence: 95%

Methyl and t-butyl reorientation in an organic molecular solid

Beckmann¹,

Dougherty²,

Kassel³

2009

Solid State Nuclear Magnetic Resonance

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We have determined the molecular and crystal structure of 4,5-dibromo-2,7-di-tbutyl-9,9-dimethylxanthene and measured the 1 H spin-lattice relaxation rate from 87 to 270 K at NMR frequencies of /2 = 8.50, 22.5, and 53.0 MHz. All molecules in the crystal see the same intra and intermolecular environment and the repeating unit is half a molecule. We have extended models developed for 1 H spin-lattice relaxation resulting from the reorientation of a t-butyl group and its constituent methyl groups to include these rotors and the 9-methyl groups. The relaxation rate data is well-fitted assuming that the t-butyl groups and all three of their constituent methyl groups, as well as the 9-methyl groups all reorient with an NMR activation energy of 15.8 ± 1.6 kJ mole . Only intramethyl and intra-t-butyl intermethyl spinspin interactions need be considered. A unique random-motion Debye (or BPP) spectral density will not fit the data for any reasonable choice of parameters. A distribution of activation energies is required.

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“…in polycrystalline samples usually show more than one rotor environment (i.e., more than one value of E) as expected [17][18][19][20][21][22][23][24][25][26] and usually (but not always 18,22 ) the NMR 1 H relaxation rate data have a unique interpretation.…”

Section: Fig 1 Schematic Pictures Of the Four Compounds Investigatementioning

confidence: 99%

Solid state 1H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: The relationship between structure and methyl group and t-butyl group rotation

Wang

Mallory

et al. 2014

The Journal of Chemical Physics

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Solid state 1H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: The relationship between structure and methyl group and t-butyl group rotation. X Wang, F B Mallory, C W Mallory, H R Odhner,* and P A Beckmann 2014 J Chem Phys 140 194304 1-15.Solid state 1H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: The relationship between structure and methyl group and t-butyl group rotation We report ab initio density functional theory electronic structure calculations of rotational barriers for t-butyl groups and their constituent methyl groups both in the isolated molecules and in central molecules in clusters built from the X-ray structure in four t-butyl aromatic compounds. The X-ray structures have been reported previously. We also report and interpret the temperature dependence of the solid state 1 H nuclear magnetic resonance spin-lattice relaxation rate at 8.50, 22.5, and 53.0 MHz in one of the four compounds. Such experiments for the other three have been reported previously. We compare the computed barriers for methyl group and t-butyl group rotation in a central target molecule in the cluster with the activation energies determined from fitting the 1 H NMR spin-lattice relaxation data. We formulate a dynamical model for the superposition of t-butyl group rotation and the rotation of the t-butyl group's constituent methyl groups. The four compounds are 2,7-di-tbutylpyrene, 1,4-di-t-butylbenzene, 2,6-di-t-butylnaphthalene, and 3-t-butylchrysene. We comment on the unusual ground state orientation of the t-butyl groups in the crystal of the pyrene and we comment on the unusually high rotational barrier of these t-butyl groups. © 2014 AIP Publishing LLC. [http://dx

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H 1 nuclear magnetic resonance spin-lattice relaxation, C13 magic-angle-spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and x-ray diffraction of two polymorphs of 2,6-di-tert-butylnaphthalene

Cited by 31 publications

References 11 publications

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

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

Methyl and t-butyl reorientation in an organic molecular solid

Solid state 1H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: The relationship between structure and methyl group and t-butyl group rotation

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