The alkene shown reacts with $HCl$ . Assume that the first-formed carbocation rearranges to a tertiary cation with the least ring strain before chloride is captured. Which structure is the major product?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: A

The alkene is vinylcyclobutane. Protonation gives a secondary cation next to the strained four-membered ring; a ring carbon migrates (ring expansion), relieving angle strain and giving the tertiary 1-methylcyclopentyl cation. Chloride capture gives 1-chloro-1-methylcyclopentane.

Practice Organic Reaction Mechanisms II: Electrophilic and Radical Reactions More on Rearranged products in electrophilic addition to drawn alkenes

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The alkene shown reacts with HCl. Assume that the first-formed carbocation rearranges to a tertiary cation with the least ring strain before chloride is captured. Which structure is the major product?

Answer: A

More questions on Rearranged products in electrophilic addition to drawn alkenes

The alkene shown reacts with $HCl$ . Assume that the first-formed carbocation rearranges to a tertiary cation with the least ring strain before chloride is captured. Which structure is the major product?