Dielectric and nuclear magnetic resonance characterization of unstable clathrate hydrates of acetaldehyde and propionaldehyde

1976 ◽  
Vol 54 (19) ◽  
pp. 3085-3088 ◽  
Author(s):  
D. W. Davidson ◽  
S. R. Gough ◽  
J. A. Ripmeester
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperatures ◽  
Proton Nmr ◽  
Clathrate Hydrates ◽  
Type Ii ◽  
Methyl Group ◽  
Line Shapes ◽  
Dielectric Absorption

Sub-MHz dielectric absorption at low temperatures is used to demonstrate the formation by acetaldehyde and propionaldehyde of unstable clathrate hydrates, probably of type II. This result is supported by the proton nmr line shapes of propionaldehyde enclathrated in D2O, which also show fast rotational tunnelling of the methyl group at 4 K.

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

1991 ◽  
Vol 46 (9) ◽  
pp. 759-769 ◽  
Author(s):  
Günter Burbach ◽  
Alarich Weiss
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperatures ◽  
Inelastic Neutron Scattering ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Methyl Group ◽  
Spin Lattice

Abstract Nuclear magnetic resonance (NMR) and inelastic neutron scattering techniques (INS) have been applied to study the rotational motions and methyl group tunneling in tetramethylstibonium iodide, [Sb(CH3)4 ] I, over er a wide temperature range. Parameters describing the [Sb(CH3)4]+ cation tumbling and the methyl group reorientation at high temperatures and quantum mechanical tunneling of the methyl groups at low temperatures were determined. The results for INS and NMR experiments at low temperatures can be explained in terms of two crystallographically inequivalent methyl groups CH3(1) and CH3(2), which were established earlier by the crystal structure determination. In the INS spectra two tunneling lines at 22.0 μeV for CH3(1) and 1.05 μeV for CH3(2) with inelastic intensities in the ratio 3:1 were observed at T = 4 K. The activation energies derived from proton NMR spin-lattice relaxation time measurements for the thermally activated methyl group rotation are 1.50 kJ/mol for CH3(1) and 3.81 kJ/mol for CH3(2). They are in accordance with the activation energies obtained from neutron fixed-window measurements. The activation energy for [Sb(CH3)4]+ cation tumbling is 50.9 kJ/mol as determined from the high temperature spin-lattice relaxation behaviour. Rotational potentials for the methyl groups are derived. For both kinds of inequivalent methyl groups the threefold potential terms dominate; three- and sixfold potential contributions are shifted by 180°

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