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JEE Main levelOne or more correct optionsDifficulty 2 of 3o4136

Which statements about the E1cB mechanism are correct?

  1. AIt requires a sufficiently acidic beta-hydrogen.
  2. BIt is the usual path for a simple alkyl iodide such as with .
  3. CThe carbanion is stabilised by an electron-withdrawing group such as or .
  4. DIt occurs without any rearrangement of the carbon skeleton.

Answer: A, C, D

E1cB depends on forming a stabilised carbanion, so an acidic beta-H and an electron-withdrawing group are needed. No carbocation is formed, so no skeletal rearrangement occurs. A simple alkyl iodide has no acidic H and undergoes E2 instead.
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