NMR study of conformation and isomerization of aryl- and heteroarylaldehyde 4-tert-butylphenoxyacetylhydrazones

The conformations of 4-tert-butylphenoxyacetylhydrazones have been investigated by different NMR methods. It was shown, that existence of the rotamers is the result of nitrogen–carbonyl bond rotation. E/Z isomerization relative to the CN double bond have been found only for pyridin-2-carbaldehyde 4-tert-butylphenoxyacetylhydrazone. Solvent effects are described with regard to the role of intra- and intermolecular hydrogen bonds. The barriers of rotation were determined by NMR-measurements at various temperatures and line shape analysis.