Question

In the IR spectrum, the absorption band due to the carbonyl group in phenyl acetate appears at:

• A. \(1800\ \text{cm}^{-1}\)
• B. \(1700\ \text{cm}^{-1}\)
• C. \(1740\ \text{cm}^{-1}\)
• D. \(1660\ \text{cm}^{-1}\)

Hint:

Aryl ester oxygen shares its lone pair with the ring, raising the C=O force constant.

Answer 1

The Correct Option is A

Compare the two resonance pathways for the ester oxygen lone pair: one into the carbonyl, one into the aromatic ring. Phenolic oxygen favors ring conjugation, drawing density away from the carbonyl pathway. Less C=O resonance means a stronger, shorter double bond, larger force constant k, and by the harmonic oscillator relation, higher wavenumber. This pushes phenyl acetate's carbonyl band up to about 1800 cm-1.

\[\boxed{1800\ \text{cm}^{-1}}\]