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1H NMR studies of solvent and substituent effects on strong intramolecular hydrogen bonds

✍ Scribed by Bogumił Brzezinski; Miroslaw Szafran

Publisher
John Wiley and Sons
Year
1981
Tongue
English
Weight
476 KB
Volume
15
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Chemical shifts of H‐bonded protons in tetrabutylammonium hydrogen maleate and 14‐substituted picolinic acid N‐oxides have been measured in a number of dry solvents, of different activity, in order to distinguish between symmetrical single minimum and asymmetrical hydrogen bonds. In tetrabutylammonium hydrogen maleate the resonance was observed at 20.70 ppm and its was independent of the nature of the solvent used. The chemical shift value of picolinic acid N‐oxide varies with the solvent. These observations suggest that the hydrogen bond is symmetrical in tetrabutylammonium hydrogen maleate but that it is asymmetrical in picolinic acid N‐oxide. The chemical shifts of substituted picolinic acid N‐oxides were correlated with σ~p~, σ~m~ and Δ~p~K~a~. The substituent and solvent effects are compared and the position of the intramolecular H‐bonded protons in picolinic acid N‐oxides are estimated and discussed.

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