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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3hx244

The halide shown is added to magnesium turnings in dry ether. Select all correct statements.

  1. AThe carbon that carried bromine becomes strongly nucleophilic and basic once magnesium inserts.
  2. BA Grignard reagent carrying a free O-H group is destroyed by protonation, so it cannot be accumulated.
  3. CSubsequent reaction with and gives 4-hydroxybutanoic acid in good yield.
  4. DProtecting the OH group first (for example as a trialkylsilyl ether) allows the Grignard reagent to be prepared.

Answer: A, B, D

Magnesium inserts into the C-Br bond and makes that carbon carbanion-like (nucleophilic and strongly basic). A free O-H group protonates this carbon, so the reagent destroys itself and cannot be accumulated; hence adding CO2 does not give the hydroxy acid in good yield. Converting the OH to a non-acidic group such as a silyl ether first removes the problem.
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