While extensively studying molecular strain dynamics, which of the following specifically structured substrates is most aggressively prone to spontaneously undergo a profound skeletal ring expansion d

Question

While extensively studying molecular strain dynamics, which of the following specifically structured substrates is most aggressively prone to spontaneously undergo a profound skeletal ring expansion during a solvolysis reaction strongly subjected to $S_N1$ conditions?

Prashant Kotian · Accepted Answer

Correct answer: C. Ring expansion is overwhelmingly driven by the intense thermodynamic desire to relieve massive internal angle strain. Cyclohexyl rings (6-membered) are virtually strain-free, so they do not expand. Five-membered rings have slight strain but are generally stable. However, cyclobutane rings (4-membered) suffer from extreme angle strain (approx internal angles). The primary carbocation generated from (bromomethyl)cyclobutane violently drives a bond migration, expanding the tight 4-membered ring into a much more stable, far less strained 5-membered cyclopentyl carbocation system.

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