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NMR study of proton transfer equilibrium in Schiff bases derived from 2‐hydroxy‐1‐naphthaldehyde and 1‐hydroxy‐2‐acetonaphthone. Deuterium isotope effects on 13 C and 15 N chemical shifts
Author(s) -
Dziembowska T.,
Rozwadowski Z.,
Filarowski A.,
Hansen P. E.
Publication year - 2001
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.949
Subject(s) - chemistry , deuterium , intramolecular force , tautomer , kinetic isotope effect , chemical shift , deuterium nmr , proton , carbon 13 nmr , proton nmr , stereochemistry , physics , quantum mechanics
The proton transfer equilibrium in series of Schiff bases derived from 2‐hydroxy‐1‐naphthaldehyde and 1‐hydroxy‐2‐acetonaphthone were measured by means of 1 H, 13 C and 15 N NMR spectra and deuterium isotope effects on 13 C and 15 N chemical shifts at variable temperature and in different solvents. The latter made it possible to investigate a broad range of equilibrium positions. All compounds exist mainly as the NH tautomer over the full range of temperatures in CDCl 3 solution. The position of the equilibrium was estimated using 1 J ( 15 N, 1 H) and 3 J ( 15 NH, 1 H) coupling constants. The correlation between deuterium isotope effects n Δ 13 C‐2(XD) or n Δ 15 N(XD), where X = O or N, and the mole fraction of the NH form show the characteristic, non‐monotonic function as for other intramolecular hydrogen bonded systems. The position of the minimum depends on substituents and the maximal negative values of n Δ 13 C‐2(XD) varies with substituents and solvents. Copyright © 2001 John Wiley & Sons, Ltd.