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GATE 2025 CY – Question 54

Organic Chemistry · Types of Reactions: Nucleophilic and electrophilic substitution reactions (both aromatic and aliphatic). Addition reactions to carbon-carbon and carbon-heteroatom (N and O) multiple bonds. Elimination reactions. Reactive intermediates – carbocation, carbanion, carbenes, nitrenes, arynes and free radicals. Molecular rearrangements. Barton decarboxylation and Barton-McCombie reaction, Hunsdiecker reaction. · 2 marks · Multiple select

The process(es) and/or intermediate(s) through which the following transformation proceeds is/are

Acid-catalyzed rearrangement of a bridged terpene to a bicyclic alcohol.
  1. 1,2-methide shift
  2. 1,3-methide shift
  3. non-classical carbocation
  4. tertiary carbocation

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Correct answer: (A) 1,2-methide shift; (C) non-classical carbocation; (D) tertiary carbocation

Explanation

Protonation generates a carbocation that undergoes a Wagner–Meerwein 1,2-methyl migration. Bridged nonclassical and tertiary carbocation descriptions occur along the rearrangement before water capture. A direct 1,3-methyl shift is not required.

Official GATE 2025 answer key: https://gate2026.iitg.ac.in/doc/download/2025_Key/CY_Keys.pdf