True symmetry or pseudosymmetry: 5-amino-1-(4-methyl­phenyl­sulfonyl)-4-pyrazolin-3-one and a comparison with its 1-phenyl­sulfonyl analogue

The title compound, C₁₀H₁₁N₃O₃S, (I), crystallizes as the NH tautomer. The two rings subtend an inter­planar angle of 72.54 (4)°. An intra­molecular hydrogen bond is formed from the NH₂ group to a sulfonyl O atom. The mol­ecular packing involves layers of mol­ecules parallel to the bc plane at x ≃ 0, 1 etc., with two classical linear hydrogen bonds (amino–sulfonyl and pyrazoline–carbonyl N—H...O) and a further inter­action (amino–sulfonyl N—H...O) completing a three-centre system with the intra­molecular contact. The analogous phenyl derivative, (II) [Elgemeie, Hanfy, Hopf & Jones (1998). Acta Cryst. C54, 136–138], crystallizes with essentially the same unit cell and packing pattern, but with two independent mol­ecules that differ significantly in the orientation of the phenyl groups. The space group is P2₁/c for (I) but P2₁ for (II), which is thus a pseudosymmetric counterpart of (I).