Question:
The aldehyde that does not respond to Fehling’s test is
The aldehyde that does not respond to Fehling’s test is
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Note that Tollen's reagent (ammoniacal silver nitrate) is reduced by both aliphatic and aromatic aldehydes, but Fehling's solution only works for aliphatic ones.
Updated On: Apr 29, 2026
- methanal
- ethanal
- propanal
- butanal
- phenylmethanal
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The Correct Option is
Solution and Explanation
Step 1: Understanding the Concept:
Fehling's test is used to distinguish between aliphatic aldehydes and aromatic aldehydes/ketones.
Step 3: Detailed Explanation:
Fehling's solution contains \(Cu^{2+}\) ions. Aliphatic aldehydes can reduce these ions to a red precipitate of cuprous oxide (\(Cu_2O\)).
However, aromatic aldehydes (like benzaldehyde, also known as phenylmethanal) do not have enough reducing power to reduce Fehling's solution.
- Options (A), (B), (C), and (D) are all aliphatic aldehydes and will give a positive test.
- Option (E) Phenylmethanal (\(C_6H_5CHO\)) is an aromatic aldehyde and will not respond to the test.
Step 4: Final Answer:
Phenylmethanal does not respond to Fehling's test.
Fehling's test is used to distinguish between aliphatic aldehydes and aromatic aldehydes/ketones.
Step 3: Detailed Explanation:
Fehling's solution contains \(Cu^{2+}\) ions. Aliphatic aldehydes can reduce these ions to a red precipitate of cuprous oxide (\(Cu_2O\)).
However, aromatic aldehydes (like benzaldehyde, also known as phenylmethanal) do not have enough reducing power to reduce Fehling's solution.
- Options (A), (B), (C), and (D) are all aliphatic aldehydes and will give a positive test.
- Option (E) Phenylmethanal (\(C_6H_5CHO\)) is an aromatic aldehyde and will not respond to the test.
Step 4: Final Answer:
Phenylmethanal does not respond to Fehling's test.
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