Benzaldehyde gives a positive test with Tollens reagent but a negative one with Fehling's solution. This shows that
- A. benzaldehyde is a ketone
- B. benzaldehyde contains no carbonyl group
- C. Fehling's solution reacts only with aromatic compounds
- D. aromatic aldehydes are oxidised less readily than aliphatic aldehydes
Explanation
Fehling's solution is the milder oxidising agent of the two, so it fails with aromatic aldehydes whose carbonyl group is stabilised by conjugation with the ring, while the stronger Tollens reagent still succeeds. Benzaldehyde is definitely an aldehyde, as the silver mirror confirms. This exception is a favourite examination point precisely because it looks like a contradiction.
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