Doi:10.1016/S0022-2860(98)00305-6

Tautomerism of NH-pyrazolinones in the solid state: the case of 3(5)-ethoxycarbonyl-5(3)-hydroxypyrazole

The molecular and crystal structure of the title compound, as determined by X-ray analysis, shows that the tautomeric form present in the solid state is 5-ethoxycarbonyl-3-hydroxypyrazole, 3. Dimers with crystallographic symmetry centres are formed through O-HżN hydrogen bonds. The relative stability of the 3(5)-hydroxypyrazole tautomers and the disposition of the ethoxycarbonyl groups with respect to the pyrazole ring have been studied by ab initio methods.