The correct answer is Option (3) → Aliphatic Aldehyde
- Fehling’s solution (alkaline Cu²⁺ complex) is reduced by compounds that can be easily oxidized to carboxylates in alkaline medium. It gives a brick-red precipitate of Cu₂O mainly with aliphatic aldehydes.
- Option-wise Explanation
- 1. Aromatic aldehyde Aromatic aldehydes like benzaldehyde generally do not reduce Fehling’s solution. The carbonyl group is stabilized by resonance with the benzene ring, making oxidation difficult.
- 2. Ketone Simple ketones lack the –CHO group and are resistant to mild oxidizing agents like Fehling’s reagent. Hence, no red Cu₂O precipitate is formed.
- 3. Aliphatic aldehyde These readily oxidize to carboxylate ions in alkaline medium. During oxidation, Cu²⁺ is reduced to Cu₂O, giving the characteristic red precipitate.
- 4. α-Hydroxy aromatic ketone Though α-hydroxy ketones can sometimes reduce Tollens’ reagent, aromatic ketone structures are less reactive toward Fehling’s solution due to stabilization and steric factors.
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