1H‐NMR‐, 13C‐NMR‐ und IR‐Untersuchungen zur Tautomerie von 15N‐markiertem 3‐Methyl‐1‐phenyl‐Δ2‐pyrazolin‐5‐on

1H‐N. M. R., 13CN. M. R., and I. R.‐Investigations Concerning Tautomerism of 15N‐Labeled 3‐Methyl‐1‐phenyl‐Δ2‐pyrazolin‐5‐one The behaviour of the 15N‐mono and dilabeled compound in dependence on temperature and solvent polarity is described. Chemical shifts, nJ(15N1H), and nJ(15N13C) coupling constants (n = 1 – 3) have been determined. In the cases of 2, 2, 2‐trifluoroethanole and hexafluoroisopropanole the Δ4‐pyrazolin‐3‐one is stabilized and detected by 3J(15N2H4) = 3 Hz, 1J(13C315N2) = 11, 0 Hz and δ(13C5). In HMPT the 5‐hydroxypyrazole form predominates and is characterized by 3J(15N1H4) = 5, 1 Hz and δ (13C5). Coupling constants 3J(15N2H4) and J(13C315N2) could not be observed in this solvent. In accordance with 1H‐ and 13C‐n. m. r.‐parameters i. r. measurements in dependence on temperature lead to the conclusion that in DMSO and THF for instance all three tautomers are present and variation of temperature does not change the equilibrium between the tautomers. A good relationship between the content of the CH2, OH and NH forms and the Donor Numbers (DN) and Acceptor Numbers (AN) by Gutmann has been found.