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

The deuterium isotope effect on the 13C NMR chemical shifts of some α‐2‐hydroxyaryl‐N‐phenylnitrones (Schiff base N‐oxides) was studied. The existence of an intramolecular hydrogen bond with the proton localized on the phenolic oxygen atom was evidenced. Exceptionally large isotope effects ΔC‐2(D) and ΔC‐α(D) suggest that the substitution of the proton of the OH group by deuterium leads to a weakening of the hydrogen bond and some conformational changes in the molecule. This conclusion was drawn on the basis of a comparison of the deuterium isotope effects of Schiff base N‐oxides and parent Schiff bases.