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1 H NMR studies of proton transfer in ortho ‐mannich bases
Author(s) -
Rospenk M.,
Sobczyk L.
Publication year - 1989
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260270505
Subject(s) - chemistry , proton , chemical shift , intermolecular force , proton nmr , acceptor , molecule , stereochemistry , organic chemistry , nuclear physics , condensed matter physics , physics
The 1 H 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 δ H versus Δp K a 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.