15N NMR study of azo-hydrazone tautomerism of 15N-labelled azo dyestuffs

¹⁵N chemical shifts of 3-methyl-1-phenylpyrazole-4,5-dione 4-phenylhydrazone (1), 4-hydroxyazobenzene (2), 2-hydroxy-5-tert-butylazobenzene (3) and 1-phenylazo-2-naphthol (4), monolabelled with ¹⁵N at α-(compounds prepared from ¹⁵N-aniline) and β-positions (compounds prepared from Na¹⁵NO₂), have been measured and the temperature dependence of these chemical shifts followed between 240 and 360 K. For 4, representing a mixture of the azo and hydrazone forms, the hydrazone content has been calculated from the ¹⁵N chemical shifts of both nitrogen atoms at various temperatures. The two calculations gave identical results.     

Über den Wassergehalt der Calciumsalze von Bernsteinsäure und Methyläthylessigsäure

Ohne ZusammenfassungBei dieser Gelegenheit erlaube ich mir noch, Herrn Hofrath Ad. Lieben, der mir stets mit Rath und That an die Hand ging, meinen verbindlichsten Dank auszusprechen.     

13C NMR spectra of non-labelled and 15N-mono-labelled azo dyes

¹³C NMR spectra of four types of azo coupling products from benzenediazonium chloride have been measured and interpreted, viz. hydrazo compounds with an intramolecular hydrogen bond (3-methyl-1-phenylpyrazole-4,5-dione 4-phenylhydrazone), azo compounds without an intramolecular hydrogen bond (4-hydroxyazobenzene), azo compounds with an intramolecular hydrogen bond (2-hydroxy-5-tert-butylazobenzene) and an equilibrium mixture of both the tautomers of 1-phenylazo-2-naphthol. The absolute values of the J(¹⁵N¹³C) coupling constants have been determined by recording the spectra of the ¹⁵N isotopomers, and have been used, in some cases, for ¹³C signal assignment. A relationship has been found between the chemical shifts of the C-1′ to C-4′ carbons of the phenyl group (from the benzenediazonium ion) or the ¹J(¹⁵N¹³C) coupling constant, and the composition of the tautomeric mixture.