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

Abstract

The deuterium isotope effect on the 13 C NMR chemical shifts of some a-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 1C-2(D) and 1C-a(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.

Studies based on deuterium isotope effect on 13C chemical shifts

“…Exceptionally large 2 DCðDÞ values and unusual signs of the other longrange isotope effects observed for some sterically hindered ortho-hydroxy acyl aromatic compounds [56] with intramolecular hydrogen bonds have been explained by a weaker hydrogen bond and higher degree of twist in the D-substituted compound [57].…”

“…The abnormally large 2 DCðDÞ values have suggested the presence of a sterically strained, non-planar chelate ring in a-(2-hydroxyaryl)-N-phenyl nitrones [57].…”

Schiff Bases Derived from 2-Hydroxynaphthalene-1-carbaldehyde and their Metal Complexes

“…4). Dziembowska et al [40] synthesized derivatives of 2-hydroxy-1-naphthaldehyde with aliphatic and heterocyclic amines (Fig. 5).…”