Abstract

The structure of the product obtained by reacting phenylhydrazine, p-chlorophenylhydrazine and hydrazine itself with dehydroacetic acid has been established by a combined use of X-ray crystallography and NMR (H-1 and C-13) spectroscopy. The X-ray structure of 1-phenyl-3-methyl-4(1-phenyl-3-methyl-1H-pyrazol-5-yl)-2H-3-pyrazolin-5-one 1d has been determined. The compound crystallizes in the space group P2(1)/a [C20H18N4O, a = 11.801(2), b = 7.911(1), c = 18.363(2) Angstrom, alpha = 90.00 degrees, beta = 100.04 degrees, gamma = 90.00 degrees, Z = 4]. The structure corresponds to the NH-tautomer of the pyrazolinone moiety; the angle of twist corresponding to pyrazole rings, defined as C1-C2-C4-C5, is -119.1(7)degrees. NMR spectrum allows to estimate the tautomeric equilibrium constant in solution and in the solid state.