Deuterium isotope effects on C-13 NMR chemical shifts of some alpha-(2-hydroxyaryl)-N-phenylnitrones (Schiff base N-oxides)

The deuterium isotope effect on the C-13 NMR chemical shifts of some alpha -2-hydroxyaryl-N-phenylnitrones (Schiff base N-oxides) was studied. The exi stence of an intramolecular hydrogen bond with the proton localized on the phenolic oxygen atom was evidenced. Exceptionally large isotope effects Del taC-2(D) and DeltaC-alpha (D) suggest that the substitution of the proton o f the OH group by deuterium leads to a weakening of the hydrogen bond and s ome conformational changes in the molecule. This conclusion was drawn on th e basis of a comparison of the deuterium isotope effects of Schiff base N-o xides and parent Schiff bases. Copyright (C) 2001 John Wiley & Sons, Ltd.