2-Methyl-3-phenyl-2,5-dihydro-1,2,4-triazin-6(1H)-one Methanol Solvate and 4-Methyl-3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one

Tautomeric detail in the two triazinones has been accurately defined. 2-Methyl-3-phenyl-2,5-dihydro-1,2,4-triazin-6(1H)-one methanol solvate, C₁₀H₁₁N₃O.CH₃OH. was found to adopt a zwitterionic form with a dihedral angle between the mean plane of the dihydrotriazinone ring (r.m.s. deviation 0.12 Å) and the phenyl ring of 44.5 (2)°. In the crystal, the molecules are linked by intermolecular hydrogen bonds between the protonated ring N atom at position 4 and the carbonyl O atom. 4-Methyl-3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one, C₁₀H₁₁N₃O, adopts a non-ionic tautomeric form. The dihedral angle between the mean plane of the dihydrotriazinone ring (r.m.s. deviation 0.15 Å) and the phenyl ring is 33.7 (1)°. The molecules in the crystal are linked into dimers by hydrogen bonds between the protonated ring N atom at position 1 and the carbonyl O atom.

-1