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JEE Chemistry 2023 Question with Solution

Identify 'A' in the given reaction to produce the major product:

Reaction scheme showing a ketone reacting with an alpha-hydroxy carboxylic acid under acidic conditions to form product A as the major product.
  • A
    Option 1 structure showing a cyclic ester-like product with tert-butyl-substituted carbon, hydroxyl group, and carbonyl group in a five-membered ring.
  • B
    Option 2 structure showing a cyclic ester product with tert-butyl-substituted carbon and carbonyl-containing five-membered ring without hydroxyl substitution.
  • C
    Option 3 structure showing an acyclic ester-like product containing hydroxyl, carbonyl, and tert-butyl-substituted fragments.
  • D
    Option 4 structure showing a cyclic intermediate-like product with hydroxyl and carboxylic acid substituents attached to a five-membered ring.

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: The unknown compound A must be identified from the reaction scheme.

Find: The major product formed under acidic conditions.

The solution states that compound A undergoes an aldol addition followed by dehydration. The reaction starts with formation of an enolate ion from the ketone. This enolate ion attacks the aldehyde equivalent center, giving a beta-hydroxy ketone intermediate, which then loses water to form the major product.

Mechanism diagram showing enolate formation, nucleophilic attack, beta-hydroxy intermediate formation, and dehydration under acidic conditions leading to the major cyclic product.

The extracted solution explicitly concludes: The Correct Option is D and Correct answer is (d).

Therefore, the correct option is D.

Common mistakes

  • Mistake: Choosing the beta-hydroxy addition product directly as the final answer. Why wrong: the reaction conditions shown in the solution proceed further to dehydration. What to do instead: identify the addition product first, then check whether loss of water gives the more stable major product.

  • Mistake: Ignoring that the ketone forms an enolate before bond formation. Why wrong: without locating the enolate-reactive site, the carbon-carbon bond is assigned incorrectly. What to do instead: first determine the enolate from the ketone and then trace its attack on the electrophilic carbon.

  • Mistake: Selecting an option only by matching functional groups visually. Why wrong: several options may contain similar groups but differ in connectivity and reaction progression. What to do instead: follow the mechanism shown in the solution and compare the final connectivity with the options.

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