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GATE 2022 CY – Question 36

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 choice

The major product P obtained in the following reaction sequence is

Diagram for GATE 2022 CY question 36
  1. Diagram A
  2. Diagram B
  3. Diagram C
  4. Diagram D

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Correct answer: (A) Diagram A

Explanation

Two methylations occur at the benzylic α-carbon under the stated conditions, giving a gem-dimethyl centre. Hydroxylamine forms the oxime. Activation with PCl5 favours Beckmann fragmentation because cleavage generates a stabilized tertiary benzylic cation; elimination yields the isopropenyl group while the oxime carbon becomes nitrile. The open-chain nitrile is **A**, rather than a ring-expanded lactam.