¹H and ¹³C NMR spectra of (<i>Z</i>)‐<i>N</i>‐(o‐hydroxy‐benzylidene)‐p‐x‐phenylamine <i>N</i>‐oxides and (<i>Z</i>)‐<i>N</i>‐(2‐hydroxy‐1‐naphthylmethylene)‐p‐X‐phenylamine <i>N</i>‐oxides

Abstract

Abstract Substituent effects on the 1 H and 13 C chemical shifts of ( Z )‐ N ‐(o‐hydroxybenzylidene)‐p‐X‐phenylamine N ‐oxides [( Z )‐α‐(o‐hydroxyphenyl)‐ N ‐p‐X‐phenyl nitrones] and ( Z )‐ N ‐(2‐hydroxy‐1‐naphthylmethylene)‐p‐X‐phenylamine N ‐oxides [(Z)‐α‐(2‐hydroxy‐1‐naphthyl)‐ N ‐p‐X‐phenyl nitrones] have been obtained. A combination of SFDOR and NOE methods was necessary for complete assignment of signals in the naphthalene series. Correlations have been found between the chemical shifts of various protons and carbons and Hammett o‐ parameters and Swain and Lupton F and R parameters. With both series of compounds a fixed conformation, due to intramolecular hydrogen bonding, is observed which affects the polarity of the nitrone group compared with that in α,N‐diphenyl nitrone. Reduced through‐resonance between aryl rings via the nitrone function was found. This may be attributed to the α‐aryl ring and the nitrone group being held out of coplanarity by the hydrogen bond.