ISSN:
0749-1581
Keywords:
1H NMR chemical shifts
;
Temperature dependence
;
Line width
;
ortho-Mannich bases
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The 1H chemical shifts of the active bridge protons and their temperature dependences were measured in various solvents for a number of ortho-Mannich bases containing proton-donor (OH) and proton-acceptor (N) centres of varying strength. It was found that a maximum on the plot of δH versus ΔpKa occurs, similar to that in intermolecular hydrogen-bonded systems, although the shape of the plot is different. The maximum is located in the critical (inversion) region where the proton transfer equilibrium takes place. The contribution of the proton transfer form increases substantially on cooling, so that one observes a dramatic temperature effect on the chemical shift for some derivatives. The line width of the bridge protons shows a sharp narrowing in the critical region, which can be interpreted as being due to the fast jumping of protons between the donor and acceptor atoms.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260270505
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