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JEE Advanced levelSingle correct optionDifficulty 3 of 3ro037

Assertion (A): Birch reduction of anisole gives 1-methoxycyclohexa-1,4-diene and not 3-methoxycyclohexa-1,4-diene. Reason (R): The electron-donating methoxy group destabilises negative charge on the ring carbon that carries it, so that carbon is not protonated and remains sp2.

  1. ABoth A and R are true but R is not the correct explanation of A
  2. BBoth A and R are true and R is the correct explanation of A
  3. CA is true but R is false
  4. DA is false but R is true

Answer: B

In the carbanion/radical-anion intermediates the donor group disfavours charge at its own carbon, so protonation occurs at other positions and the OMe-bearing carbon stays in a double bond. This explains the observed regiochemistry; both statements are true and R explains A.
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