The compound shown is the hydroxy form of a heteroaromatic lactam. In water it exists mainly as which of the tautomers shown?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: B

The compound is 2-hydroxypyridine, whose tautomer 2-pyridone predominates in water and in the solid state. The amide-like C=O...N-H form is strongly stabilised by polar solvents and hydrogen-bond dimerisation, and still has aromatic character through the dipolar resonance form. The hydroxy form is only slightly favoured in the gas phase.

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