Question

The compound 2-hydroxypyridine, a derivative of pyridine, is in equilibrium with 2-pyridone. 2-Hydroxypyridine is aromatic. Does 2-pyridone have comparable aromatic character? Explain.

Short answer

Explain your answer. Answer: Yes, both 2-hydroxypyridine and 2-pyridone have comparable aromatic characters because they each contain six delocalized π-electrons in their respective rings, which follow the Hückel rule for aromaticity. Although 2-pyridone has a resonance structure, this does not affect its aromatic character.

Step-by-step solution

Drawing the structures of 2-hydroxypyridine and 2-pyridone

Begin by drawing the structures of the two compounds, 2-hydroxypyridine and 2-pyridone. This will help in visualizing the molecules and understanding their electronic properties. 2-hydroxypyridine: O || C-C=C-N-C=C \ / H 2-pyridone: O || C-C=C-N=C-C \

Identify the aromaticity in 2-hydroxypyridine

2-hydroxypyridine is aromatic because it has six π-electrons delocalized over the six atoms in the ring. This happens due to double bonds between three pairs of atoms, including the nitrogen atom. This delocalization of electrons follows the Hückel rule, which states than an aromatic compound must have (4n+2) π-electrons, where n is a whole number.

Analyzing the aromaticity in 2-pyridone

In 2-pyridone, the oxygen atom forms a double bond with the carbon atom. This introduces an extra double bond in the molecule. However, the overall electron count remains the same. The molecule still has six π-electrons, as the case with 2-hydroxypyridine.

Evaluate the resonance structures of 2-pyridone

2-pyridone has a resonance structure where the double bond between oxygen and carbon is broken, and the electrons localize on the oxygen atom. This is due to the higher electronegativity of oxygen compared to carbon. This move would cause the formation of a new double-bond between nitrogen and carbon atoms. The resonance structure would look like this: O- | C=N-C=C-N=C-C The new resonance structure shows that the molecule still maintains the six π-electrons delocalized over six atoms in the ring.

Compare the aromatic characters of both compounds and conclude

2-hydroxypyridine and 2-pyridone both possess aromatic character, as they each contain six delocalized π-electrons in their respective rings. Even though 2-pyridone has a resonance structure because of the oxygen's higher electronegativity, this does not affect the aromatic character of the molecule. Therefore, it can be concluded that 2-pyridone has comparable aromatic character to 2-hydroxypyridine.