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1 H NMR studies of solvent and substituent effects on strong intramolecular hydrogen bonds
Author(s) -
Brzezinski Bogumił,
Szafran Miroslaw
Publication year - 1981
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270150116
Subject(s) - picolinic acid , substituent , chemistry , hydrogen bond , intramolecular force , solvent , chemical shift , inorganic chemistry , medicinal chemistry , molecule , stereochemistry , organic chemistry
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.