Structure and tautomerism om maleic hydrazide

The structure and tautomerism of maleic hydrazide were examined by means of quantum chem- ical methods. The molecular geometry of the various tautomers and their stability order were determined by employing the 3-21G and 6-31G* basis sets. The solvent influence on the stability of the tautomers was estimated by means of a quantum chemical continuum model. The results indicate the monohydroxy-monoketo tautomer as the most stable one in the gas phase followed by the diketo form, which becomes of comparable importance in solution. Compared with the other tautomers, the diketo tautomer exhibits a distinct nonplanar structure