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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g3234

The cation shown is generated in solution and rearranges. Which statements are correct? Select all that apply.

  1. AThe rearranged cation is less stable than the cation shown because it has more substituents.
  2. BA 1,2-methyl shift gives the 2-methylbutan-2-yl cation.
  3. CThe rearranged cation can lose a proton to give two different alkenes, 2-methylbut-2-ene and 2-methylbut-1-ene.
  4. DNo 1,2-hydride shift is possible because the carbon next to the cationic carbon bears no hydrogen.

Answer: B, C, D

The cation shown is the neopentyl cation. Its neighbouring carbon is quaternary, so no 1,2-hydride shift is available (statement D true). A 1,2-methyl shift gives the tertiary 2-methylbutan-2-yl cation (statement B true), which is more stable, not less, than the primary cation (statement A false). Deprotonation of the tertiary cation at a CH or at the CH gives 2-methylbut-1-ene or 2-methylbut-2-ene (statement C true).
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