Nuclear spin-lattice relaxation in long chain viscous hydrocarbons

Cutnell, John D.; Schisla, R. M.; Hammann, W. C.

doi:10.1021/j100628a011

Cited by 10 publications

(4 citation statements)

References 5 publications

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“…Highly methyl-branched long chain hydrocarbons (C 26 −C 32 ) in the viscous state have activation energies ranging from 26 to 37 kJ/mol . However, for nonviscous liquids, Agishev reported an activation energy of 12.1 kJ/mol for normal paraffins hexane, dodecane, and octadecane in CCl 4 , and Woessner et al .…”

Section: Resultsmentioning

confidence: 99%

“…Highly methyl-branched long chain hydrocarbons (C 26 -C 32 ) in the viscous state have activation energies ranging from 26 to 37 kJ/mol. 46 However, for nonviscous liquids, Agishev 47 reported an activation energy of 12.1 kJ/mol for normal paraffins hexane, dodecane, and octadecane in CCl 4 , and Woessner et al 48 reported a value of 17.0 kJ/mol for neat n-dodecane. The activation energies for normal alkanes (C 6 -C 40 ) in the solid state were reported to be 10.9 kJ/mol and were ascribed to the 3-fold reorientation of the methyl group.…”

Section: Apparent Activation Energies For Molecular Motions Of Aromat...mentioning

confidence: 99%

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Apparent Activation Energies for Molecular Motions in Solid Asphalt

Netzel

2006

Energy Fuels

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The hydrogen spin−lattice relaxation time in the rotating frame was measured for three whole asphalts at temperatures ranging from 20 to −45 °C. These data were used to calculate the apparent activation energies for the molecular motion of the aromatic and aliphatic components found in asphalt. The measured activation energies ranged from 8.8 to 9.8 kJ/mol for the aliphatic components in the three asphalts and were attributed to rapid methyl rotation of the terminal and branched methyl groups on the long carbon chainlength alkanes. The apparent activation energies measured for the molecular motion of the aromatic components in the three asphalts ranged from 6.5 to 7.2 kJ/mol. The low barrier to molecular motion observed for the aromatic constituents can be explained by two mechanisms. The first mechanism is spin−diffusion interaction of the aromatic ring hydrogens with the aliphatic hydrogens of the rapidly rotating methyl substituents on aromatic rings. The second mechanism is the in-plane rotation of relatively small polycondensed aromatic molecules and torsional oscillations of pendant phenyl groups as guest molecules within a nanopore matrix of rigid-amorphous aliphatic components.

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Section: Resultsmentioning

confidence: 99%

Section: Apparent Activation Energies For Molecular Motions Of Aromat...mentioning

confidence: 99%

Apparent Activation Energies for Molecular Motions in Solid Asphalt

Netzel

2006

Energy Fuels

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“…[52,53] This phenomenon is a result of cross correlations among the three spin-1/2 protons (or three spin-1/2 19 F nuclei) and is well understood [52,53] and well established experimentally. [51,[54][55][56][57][58] The relaxation becomes more exponential if the methyl group rotation axis is reorienting, such as in a t-butyl group [48,49] or for whole-molecule rotation. [57,[59][60][61] It also becomes more exponential if CH 3 -non-CH 3 1 H-1 H interactions play a significant role.…”

Section: Introduction: General Featuresmentioning

confidence: 99%

Proton Spin‐Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation

et al. 2018

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We report solid-state nuclear magnetic resonance H spin-lattice relaxation, single-crystal X-ray diffraction, powder X-ray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry in solid samples of 2-ethylanthracene (EA) and 2-ethylanthraquinone (EAQ) that have been physically purified in different ways from the same commercial starting compounds. The solid-state H spin-lattice relaxation is always non-exponential at high temperatures as expected when CH rotation is responsible for the relaxation. The H spin-lattice relaxation experiments are very sensitive to the "several-molecule" (clusters) structure of these van der Waals molecular solids. In the three differently prepared samples of EAQ, the relaxation also becomes very non-exponential at low temperatures. This is very unusual and the decay of the nuclear magnetization can be fitted with both a stretched exponential and a double exponential. This unusual result correlates with the powder X-ray diffractometry results and suggests that the anomalous relaxation is due to crystallites of two (or more) different polymorphs (concomitant polymorphism).

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“…Hilt and Hubbard [2] performed a numerical averaging over all orientations of the CH 3 (or CF 3 ) group rotation axes appropriate for a polycrystalline powder and found that the relaxation is still nonexponential, particularly near the relaxation rate maximum (ωτ ~ 1) and at higher temperatures (ωτ < 1). Nonexponential spin-lattice relaxation has been observed in polycrystalline solids [34][35][36][37][38][39][40][41] in temperature regions corresponding to ωτ ~ 1 and ωτ < 1. All these studies report exponential relaxation (within experimental uncertainty) at lower temperatures…”

Section: Introductionmentioning

confidence: 99%

Nonexponential 1H spin–lattice relaxation and methyl group rotation in molecular solids

Beckmann

2015

Solid State Nuclear Magnetic Resonance

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We report a quantitative measure of the nonexponential 1 H spin-lattice relaxation resulting from methyl group (CH 3 ) rotation in six polycrystalline van der Waals solids. We briefly review the subject in general to put the report in context. We then summarize several significant issues to consider when reporting 1 H or 19 F spin-lattice relaxation measurements when the relaxation is resulting from the rotation of a CH 3 or CF 3 group in a molecular solid. IntroductionIn 1964, Runnells [1] and, independently, Hilt and Hubbard [2] showed that the nuclear spinlattice relaxation resulting from the modulation of the spin-spin interactions among the three spin- This phenomenon is often neglected, which means that, knowingly or unknowingly, an average relaxation rate is reported. Here, following a brief review of this subject, we pull together results from six polycrystalline van der Waals organic solids with quite different methyl group environments and quite different motions of the methyl group rotation axes, to show that this phenomenon is ubiquitous. We also show that the relaxation at lower temperatures, though always reported as being exponential within experimental uncertainty, can, in a statistical sense when many experiments are considered, be seen also to be slightly nonexponential.Background

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Nuclear spin-lattice relaxation in long chain viscous hydrocarbons

Cited by 10 publications

References 5 publications

Apparent Activation Energies for Molecular Motions in Solid Asphalt

Apparent Activation Energies for Molecular Motions in Solid Asphalt

Proton Spin‐Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation

Nonexponential 1H spin–lattice relaxation and methyl group rotation in molecular solids

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