¹H‐, ¹³C‐ und ¹⁵N‐NMR‐Untersuchungen zur Tautomerie von Bispyrazolonen vom Typ der 4,4′‐Methyliden‐bis‐(3‐stearoylamino‐1‐phenyl‐pyrazolin‐5‐one)

Abstract

1H‐N.M.R., 13C‐N.M.R., and 15N‐N.M.R.‐Investigations Concerning Tautomerism of Bispyrazolons of 4,4′‐Methyliden‐bis‐(3‐stearoylamino‐1‐phenyl‐pyrazolin‐5‐on) Type With the help of 1H, 13C and 15N chemical shifts of the n.m.r. signals of the structure elements OH, NHCO, 13C‐5, 15N‐1, 15N‐2 and 15N‐2‐H and using the coupling constants nJ(15NH) and nJ(13C15N) (n = 1, 2) of the doubly 15N labelled bispyrazolone 1, a chelated and an associated species were shown to exist in the slightly polar solvent CDCl3. The chelated bispyrazolone (BC)ch contains one pyrazolone ring in the tautomeric NH form B and the other in the tautomeric OH form C. In the associated bispyrazolone (BB)as, both pyrazolone rings exist in the NH form B. Observation of the time, concentration and temperature dependence of the n.m.r. spectra of 1 resulted in the detection of complex exchange processes in tautomeric equilibrium. Apart from the intermolecular exchange process (BC)ch ⇌ (BB)as, another exchange process (BC)ch ⇌ (CB)ch occurs, with intermolecular interactions being involved. It has been established that in the case of substitution in the methylidene bridge (2, 3) the lefthand side of the equilibrium (BC)ch ⇌ (BB)as participates in the process to a greater extent than in the case of 1 (unsubstituted methylidene bridge).