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 determin ed by X-ray analysis, shows that the tautomeric form present in the so lid state is 5-ethoxycarbonyl-3-hydroxypyrazole, 3. Dimers with crysta llographic symmetry centres are formed through O-H...N 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. (C) 1998 Elsevier Science B.V. All rights reserved.