Studies of chemical exchange by nuclear magnetic resonance. II. Hindered rotation in amides and thioamides

1967 ◽  
Vol 89 (14) ◽  
pp. 3412-3416 ◽  
Author(s):  
Robert C. Neuman ◽  
David N. Roark ◽  
Violet. Jonas
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Exchange ◽  
Hindered Rotation ◽  
Nuclear Magnetic

Nuclear Magnetic Resonance Studies of Multi-site Chemical Exchange. III. Hindered Rotation in Dimethylacetamide, Dimethyl Trifluoro-acetamide, and Dimethyl Benzamide

1971 ◽  
Vol 49 (22) ◽  
pp. 3683-3691 ◽  
Author(s):  
L. W. Reeves ◽  
R. C. Shaddick ◽  
K. N. Shaw
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Exchange ◽  
Chemical Shifts ◽  
Activation Parameters ◽  
Type Systems ◽  
Hindered Rotation ◽  
Fitting Procedure ◽  
Nuclear Magnetic

The experimental application of a multi-site exchange theory developed recently has been made to three restricted rotation barriers in amido-type systems. Inclusion of 8 spin-sites in the analyses of the line shapes for spectra of N,N-dimethyl trifluoroacetamide and dimethyl acetamide leads to improved values for the activation parameters. Variation of chemical shifts with temperature is included in the iterative fitting procedure. The determination of the relative signs of long range couplings and the inclusion and measurement of unresolved couplings has been accomplished. The barrier for hindered rotation in N,N-dimethyl benzamide has been re-investigated including the effect of relatively large chemical shift changes with temperature. The internal consistency of the measurements from all aspects indicates that systematic errors common in the determination of energy barriers by steady-state nuclear magnetic resonance (n.m.r.) have been largely eliminated and hence the activation parameters obtained form a reliable addition to a compilation of experimental data pertaining to the bonding in a related series of simple C-substituted amides.

Nuclear Magnetic Resonance Studies of Multi-site Chemical Exchange. II. Hindered Rotation in N,N-Dimethyl Carbamyl Fluoride

1971 ◽  
Vol 49 (22) ◽  
pp. 3671-3682 ◽  
Author(s):  
L. W. Reeves ◽  
K. N. Shaw
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Exchange ◽  
Chemical Shifts ◽  
Activation Parameters ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Matrix Formulation ◽  
Hindered Rotation ◽  
Nuclear Magnetic

The matrix formulation of the Bloch equations including chemical exchange reported earlier is extended to include indirect spin–spin coupling in first-order spectra. The ABX (JAB = 0) spin system is treated in detail and particular attention is paid to the determining effect on the nuclear magnetic resonance (n.m.r.) lineshapes of the relative signs of the coupling constants JAX and JBX. The hindered rotation for N,N-dimethyl carbamyl fluoride in CCl4 as solvent has been studied using a complete 1H n.m.r. lineshape analysis and the activation parameters obtained are: ΔG≠ = 18.1 ± 0.6 kcal mol−1, ΔH≠ = 17.7 ± 0.6 kcal mol−1, and ΔS≠ = −1.4 ± 2.1 cal deg−1 mol−1 at 25 °C.The complete lineshape fits give very precise values of the relative shifts (16.5 mol% in CCl4) of the methyl groups and of the coupling constants JAX (0.30 ± 0.05 Hz) and JBX (0.80 ± 0.05 Hz) at all temperatures. A 40% change in JBX (1.10 ± 0.05 Hz) is observed in neat DMCF from a lineshape fit at −15 °C. The origin of changes in chemical shifts with temperature and JBX with solvent is discussed.

Chemical exchange at the ferroelectric phase transition of lead germanate revealed by solid state 207Pb nuclear magnetic resonance

2019 ◽  
Vol 21 (3) ◽  
pp. 1100-1109 ◽  
Author(s):  
Claudia E. Avalos ◽  
Brennan J. Walder ◽  
Jasmine Viger-Gravel ◽  
Arnaud Magrez ◽  
Lyndon Emsley
Keyword(s):  
Phase Transition ◽  
Nuclear Magnetic Resonance ◽  
Solid State ◽  
Magnetic Resonance ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Chemical Exchange ◽  
Lead Germanate ◽  
Mixed Order ◽  
Nuclear Magnetic

Multi-dimensional NMR is used to quantitatively identify a mixed order–disorder and displacive mechanism for the ferroelectric phase transition of lead germanate.

Nuclear Magnetic Resonance Studies of some Trimethyl Tin Carbamates

1972 ◽  
Vol 50 (9) ◽  
pp. 1386-1389 ◽  
Author(s):  
A. E. Lemire ◽  
J. C. Thompson
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Chloroform Solution ◽  
Activation Parameters ◽  
Hindered Rotation ◽  
Magnetic Resonance Studies ◽  
Hexane Solution ◽  
Nuclear Magnetic

The low temperature n.m.r. spectra of some trimethylstannyl esters of N,N-dimethylcarbamic acid, N,N-dimethyldithiocarbamic acid, and N,N-dimethylmonothiocarbamic acid have been examined. Activation parameters for hindered rotation about the C—N bond in the trimethylstannyl ester of N,N-dimethylmonothiocarbamic acid have been determined to be: in hexane solution, Ea = 17.0 + 0.5 kcal/mol, [Formula: see text][Formula: see text][Formula: see text] in chloroform solution, Ea = 19.9 ± 0.5 kcal/mol, [Formula: see text][Formula: see text][Formula: see text]not available

Nuclear Magnetic Resonance Methods for Determining Chemical-Exchange Rates1

1966 ◽  
Vol 88 (14) ◽  
pp. 3185-3194 ◽  
Author(s):  
Adam Allerhand ◽  
H. S. Gutowsky ◽  
J. Jonas ◽  
R. A. Meinzer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Exchange ◽  
Nuclear Magnetic
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