ChemInform Abstract: Nonexponential 1H Spin-Lattice Relaxation and Methyl Group Rotation in Molecular Solids

ChemInform ◽  
2016 ◽  
Vol 47 (31) ◽  
Author(s):  
Peter A. Beckmann
Keyword(s):  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Molecular Solids ◽  
Methyl Group ◽  
Spin Lattice ◽  
Group Rotation ◽  
Methyl Group Rotation

Relaxation Processes in Aromatic Methyl-Groups. I. 2-Chloro-Toluene and 2,6-Dichloro-Toluene

1986 ◽  
Vol 39 (12) ◽  
pp. 2049 ◽  
Author(s):  
DJ Craik ◽  
RM Drew ◽  
I Kyratzis ◽  
ID Rae ◽  
JA Weigold
Keyword(s):  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Relaxation Processes ◽  
Molecular Orbital Calculations ◽  
Relaxation Rates ◽  
Methyl Group ◽  
Spin Lattice ◽  
Group Rotation ◽  
Methyl Group Rotation

Three series of selectively deuterated toluenes, 2-chlorotoluenes and 2,6-dichlorotoluenes have been synthesized, and their methyl group 1H n.m.r. relaxation pathways have been determined by 1H, 2H and 13C n.m.r. spin-lattice relaxation time measurements. 1H spin-lattice relaxation in the methyl groups of these series occurs predominantly through an intramethyl H-H dipolar mechanism as well as through the spin-rotation mechanism. Dipolar spin-lattice relaxation rates for intramethyl H-H pairs are 0.012, 0.020 and 0.025 s-1 for toluene, 2,6-dichlorotoluene and 2-chlorotoluene respectively, suggesting a decrease in the rate of methyl group rotation in this order. Ab initio molecular orbital calculations on the same compounds show that the theoretically predicted barrier to methyl group rotation increases in the order toluene < 2,6-dichlorotoluene < 2-chlorotoluene, supporting the experimentally derived results.

Molecular Motions in Solid [Sb(CH3)4]PF6. A Combined 11H,9F Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Study

1992 ◽  
Vol 47 (5) ◽  
pp. 689-701 ◽  
Author(s):  
Günter Burbach ◽  
Norbert Weiden ◽  
Alarich Weiss
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Methyl Group ◽  
Temperature Range ◽  
Spin Lattice ◽  
Group Rotation ◽  
Methyl Group Rotation

Abstract The molecular dynamics of tetramethylstibonium hexafluorophosphate, [Sb(CH3)4]PF6, is investigated over a broad temperature range. NMR spin lattice relaxation times T1 and the NMR second moments of the 1H and 19F nuclei were determined in the range 8.6 ≦ T/K ≦ 332.3 for polycrystalline [Sb(CH3)4]PF6. The complex cation undergoes isotropic tumbling for T > 260 K and thermally activated methyl group rotation in the temperature range T < 196 K. The activation energies for the transition from methyl group rotation to cation reorientation, as derived from NMR wideline (18.1 kJ/mol) and relaxation (22.7 kJ/mol) measurements, match. At very low temperatures pseudo classical line narrowing is observed, indicating tunneling motions of the methyl groups. The existence of two crystallographically inequivalent methyl groups is found by X-ray structure analysis at room temperature. The space group is P63mc, Z = 2; a = 738.6 pm, c = 1089.3 pm. It is confirmed by two steps in the temperature dependence of the signal intensity of the quasielastic line in neutron fixed window measurements in the temperature range 2 < T/K <148. The low temperature spin lattice relaxation times can be explained qualitatively by contributions of two crystallographically inequivalent methyl groups. Apparent activation energies for the two crystallographically different methyl groups are estimated. The complex anion undergoes isotropic tumbling in the temperature range 95 < T/K < 330. Above 330 K additionally translational motion is activated. Below 95 K the rotational motion of PF-6 is freezing in via an uniaxial state in range 40 < T/K <80. Activation energies for both isotropical tumbling (10.5 kJ/mol) and uniaxial rotation (5.8 kJ/mol) have been derived from 19F NMR spin lattice relaxation

scholarly journals Proton spin-lattice relaxation and methyl group rotation

1978 ◽  
Vol 32 (3) ◽  
pp. 391-402 ◽  
Author(s):  
Peter Beckmann ◽  
Christopher I Ratcliffe ◽  
Basil A Dunell
Keyword(s):  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Methyl Group ◽  
Spin Lattice ◽  
Group Rotation ◽  
Methyl Group Rotation
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