Question #44612

This problem tests a multi-layered exception to standard ether cleavage rules.

The first trap is kinetic: students often default to $S_N2$ cleavage for ethers with HI, predicting attack on the less hindered methyl group (Option D).

However, the presence of a tertiary carbon forces an $S_N1$ pathway.

The second trap is thermodynamic: students who correctly identify the $S_N1$ pathway might stop at the initial $3^\circ$ carbocation (Option B).

The hidden variable is the ring strain of cyclobutane.

Advanced students must recognize that the relief of ring strain provides enough driving force to temporarily form a $2^\circ$ carbocation from a $3^\circ$ one.

The final trap is stopping after the ring expansion (Option C), failing to account for the subsequent 1,2-methyl shift that restores the carbocation to a $3^\circ$ state before the halide attack.