6-Methyl-2-pyridone: an elusive structure finally solved.

The title compound, C6H7NO, crystallizes unsolvated from dry toluene after storage for several months at approximately 263 K. Synchrotron radiation was needed in order to carry out data collection because of the small size of the crystals obtained. There are four crystallographically independent molecules in the asymmetric unit. Packing diagrams show that the molecules are linked into infinite chains by hydrogen bonding; two of the four independent molecules link together to form a chain, while the other two molecules form chains involving only their own symmetry equivalents, giving a total of three crystallographically distinct chains in all. The chains are held together by weak pi-pi interactions. This structure provides conclusive proof that, in the absence of any other co-crystallized molecule or solvent, the compound exists in the solid state as the pyridone and not the pyridinol tautomer.