Four Simple Pyridazin-3(2H)-ones

The structures of four simple pyridazin-3(2H)-ones, the isomeric 4-methylpyridazin-3(2H)-one [C₅H₆N₂O (5)], 5-methylpyridazin-3(2H)-one monohydrate and 6-methylpyridazin-3(2H)-one monohydrate [C₅H₆N₂O.H₂O, (6).H₂O and (7).H₂O] and 2-(p-tolyl)pyridazin-3(2H-one [C₁₁H₁₀N₂O (8)], have been determined. Compounds (6)–(7), which crystallize as monohydrates, show extensive bonding while molecules of (5) form hydrogen-bonded dimers. In (8) there are no strong hydrogen bonds as in compounds (5) and (7), the closest intermolecular contacts being pairwise C—H...O interactions.

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