Which among the given molecules can exhibit tautomerism? 1. Both I and III 2. Both I and II 3. Both II and III 4. III only

Answer: 4. III only Key idea: keto-enol tautomerism needs an alpha-H, and the enol must be able to form (a double bond at a bridgehead is not allowed, by Bredt's rule). I: the C=O is on the one-carbon bridge; its alpha carbons are bridgeheads, so the enol would have a bridgehead double bond. Not possible. II: one alpha carbon has two Ph (no H); the other is a bridgehead. Not possible. III: has an alpha CH₂ away from the bridgehead, so enolisation is possible. Only III shows tautomerism.

Topic: Structural isomerism and stereoisomerism· Some Basic Principles of Organic Chemistry

Which among the given molecules can exhibit tautomerism?

three bicyclic ketone structures I, II, III

1. Both I and III

2. Both I and II

3. Both II and III

4. III only

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Answer: 4. III only

Key idea: keto-enol tautomerism needs an alpha-H, and the enol must be able to form (a double bond at a bridgehead is not allowed, by Bredt's rule).

I: the C=O is on the one-carbon bridge; its alpha carbons are bridgeheads, so the enol would have a bridgehead double bond. Not possible.
II: one alpha carbon has two Ph (no H); the other is a bridgehead. Not possible.
III: has an alpha \(CH_2\) away from the bridgehead, so enolisation is possible.

Only III shows tautomerism.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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Which among the given molecules can exhibit tautomerism?

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