5-Amino-1-phenylsulfonyl-4-pyrazolin-3-one

The title compound, C₉H₉N₃O₃S, crystallizes with two independent molecules in P2₁, although the symmetry is close to P2₁/c. The keto tautomer is the only solid-state form. The main difference between the two molecules is the orientation of the phenyl rings. The five-membered rings are planar. An extensive hydrogen-bonding system connects the molecules into layers parallel to the xy plane.

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