The alkene shown reacts with $HCl$ to give a ring-expanded product. Assume that the carbocation keeps rearranging until the most stable carbocation accessible by 1,2-shifts is reached, and only then is chloride captured. Select all correct statements.

AThe first-formed cation is secondary.
BRing expansion relieves angle strain of the four-membered ring.
CThe final product is a tertiary alkyl chloride.
DThe final product contains a stereocentre.

Answer: A, B, C

The alkene is vinylcyclobutane. Protonation gives a secondary cation exocyclic to the cyclobutane; migration of a ring bond gives a secondary cyclopentyl cation with less strain, and a 1,2-hydride shift then gives the tertiary 1-methylcyclopentyl cation. The product 1-chloro-1-methylcyclopentane is tertiary and achiral (it has a plane of symmetry), so statement D is false.

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 to give a ring-expanded product. Assume that the carbocation keeps rearranging until the most stable carbocation accessible by 1,2-shifts is reached, and only then is chloride captured. Select all correct statements.

Answer: A, B, C

More questions on Rearranged products in electrophilic addition to drawn alkenes

The alkene shown reacts with $HCl$ to give a ring-expanded product. Assume that the carbocation keeps rearranging until the most stable carbocation accessible by 1,2-shifts is reached, and only then is chloride captured. Select all correct statements.