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MCQMediumJEE 2023Reaction Mechanisms (Substitution, Addition, Elimination)

JEE Chemistry 2023 Question with Solution

Find out the major product for the following reaction:

Starting organic substrate showing a cyclobutane ring attached to a tertiary alcohol side chain with a methyl substituent, reacted with hydronium ion.

→\rightarrow Major Product

Four product options labeled 1 to 4, showing different alkene structures formed from dehydration and possible ring-expanded or exocyclic double-bond products.
  • A

    (1)

  • B

    (2)

  • C

    (3)

  • D

    (4)

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: The reaction is dehydration of a secondary alcohol under acidic conditions, shown with H3O+\text{H}_3\text{O}^+.

Find: The major alkene product among the given options.

Under acidic conditions, the −OH-\text{OH} group is first protonated and leaves as water, giving a carbocation intermediate. The reaction then proceeds by elimination.

The major product is decided by alkene stability. According to Zaitsev's rule, the more substituted alkene is favored.

The mechanism described is:

  1. Protonation of the alcohol group.
  2. Loss of water to form a carbocation.
  3. Elimination of a proton to form the alkene.

Thus, the major product is the structure with the double bond in the more substituted position. The solution states that the correct option is C.

Therefore, the correct option is C.

Common mistakes

  • Choosing the less substituted alkene. This is wrong because acid-catalyzed dehydration generally follows Zaitsev's rule. Compare alkene substitution before selecting the product.

  • Treating the reaction as a direct loss of −OH-\text{OH} without protonation. This is wrong because −OH-\text{OH} is a poor leaving group; it leaves after protonation as water.

  • Ignoring the carbocation intermediate. This is wrong because the stability of the carbocation influences the elimination pathway. First identify the carbocation formed, then predict the alkene.

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