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Question 45

Find out the major product for the following reaction

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Under acidic conditions, the hydroxyl group is first protonated to form a good leaving group ((-OH_2^+)). Loss of water then generates a secondary carbocation at the carbon bearing the hydroxyl group.

Since this carbocation is adjacent to a four-membered ring, ring expansion occurs to relieve ring strain. The cyclobutane ring expands to form a more stable six-membered cyclohexane ring, generating a rearranged carbocation.

The rearranged carbocation can further undergo hydride or alkyl shifts to produce the most stable tertiary carbocation. Elimination of a proton from an adjacent carbon then gives the alkene product.

According to Zaitsev’s rule, the major product is the most substituted alkene. Among the given options, Option B corresponds to a tetrasubstituted alkene, whereas the green-checked option corresponds to a less substituted trisubstituted alkene.

Since tetrasubstituted alkenes are thermodynamically more stable than trisubstituted alkenes, the rearrangement and elimination sequence favors the formation of the product shown in Option B.

Hence, the major product is

$$\boxed{\text{Option B}}.$$

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