The alkene shown reacts with HBr. Which of the structures shown are carbocation intermediates that actually lie on the pathway to the products (the cation formed first, or the cation formed after a rearrangement to a more stable cation)? Select all that apply.

AStructure A
BStructure B
CStructure C
DStructure D

Answer: B, C

The alkene shown is 3,3-dimethylbut-1-ene. Protonation of C1 follows Markovnikov's rule and gives the secondary 3,3-dimethylbutan-2-yl cation. A 1,2-methyl shift then gives the tertiary 2,3-dimethylbutan-2-yl cation. The primary cations would result from protonation at C2 (anti-Markovnikov) or from unfavourable shifts and are not formed.

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The alkene shown reacts with HBr. Which of the structures shown are carbocation intermediates that actually lie on the pathway to the products (the cation formed first, or the cation formed after a rearrangement to a more stable cation)? Select all that apply.

Answer: B, C

More questions on Carbocation rearrangements from drawn cations