Phthalazin‐1(2 H )‐one

The molecule of the title compound, C 8 H 6 N 2 O, is almost planar, with a dihedral angle of 0.52 (7)° between the two rings. In the crystal structure, intermolecular N—H...O, C—H...N and C—H...O hydrogen bonds and π–π interactions link the molecules into a three‐dimensional network. The π–π interaction occurs between the pyridazinone and benzene rings of the molecules at () and (); the centroid–centroid distance is 3.588 (1) Å and the plane–plane separation is 3.434 Å.