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🧪 Chemistry  ·  Aldehydes, Ketones and Carboxylic Acids  ·  NEET & JEE

Which compound gives a positive iodoform test but a negative Tollens' test?

Answer: Acetone.

  • A Acetone
  • B Acetaldehyde
  • C Formaldehyde
  • D Benzaldehyde

Correct answer: A. Acetone

Explanation: Acetone has the CH3CO- group (iodoform positive) but is a ketone (Tollens' negative).

Nucleophilic Addition to C=ONu:-CORR'CO-RR'Nu

Curved arrows show the nucleophile attacking the carbonyl carbon while the C=O pi electrons move onto oxygen, giving a tetrahedral alkoxide intermediate.

Concept context

Aldehydes, ketones, carboxylic acids, and their derivatives (esters, amides, acid chlorides). Key reactions include nucleophilic addition, Aldol condensation, Cannizzaro, and Claisen. Very heavily tested in JEE and NEET.

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