MCQMediumJEE 2023Reaction Mechanisms (Substitution, Addition, Elimination)

JEE Chemistry 2023 Question with Solution

Find out the major products from the following reaction sequence:

Reaction scheme showing p-chloroacetophenone reacting by two paths: with NaCN then EtOH, H3O+ to give A, and with excess MeMgBr followed by H3O+ to give B.
  • A
    Option A shows product A as a cyanohydrin hydrolysis product with CO2H and OH on the same benzylic carbon, and product B as a diol formed after excess MeMgBr addition.
  • B
    Option B shows product A as an ester-containing compound with HO and CO2Et on the same benzylic carbon, and product B as a substituted diol after Grignard addition.
  • C
    Option C shows product A as a cyanohydrin with CN and OH on the benzylic carbon, and product B as an amino alcohol containing NH2 after further transformation.
  • D
    Option D shows product A with nitrile substitution on the ring and NC and OH on the benzylic carbon, and product B as a benzylic diol chain with methyl substituents.

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: The substrate undergoes two separate reaction sequences to form A and B.

Find: The major products corresponding to A and B.

From the extracted solution:

  1. NaCN\text{NaCN} reacts with the carbonyl group to form a cyanohydrin, so A contains CN-\text{CN} and OH-\text{OH} on the same carbon.
  2. The next step converts this intermediate to the major product pattern identified in the solution, and the source explicitly concludes that the products match option D.

Therefore, the correct option is D.

Explanation from Reaction Pattern

Given: The first sequence uses NaCN\text{NaCN} followed by acidic conditions, and the second uses excess MeMgBr\text{MeMgBr} followed by H3O+\text{H}_3\text{O}^+.

Find: Which option shows the final major products.

The solution text states that cyanide attacks the carbonyl carbon to give a cyanohydrin intermediate. It then identifies the final major products as those shown in option (4). Since option numbering maps as 1A1 \to A, 2B2 \to B, 3C3 \to C, 4D4 \to D, the answer is D.

Thus, the major products are those drawn in option D.

Common mistakes

  • Assuming NaCN\text{NaCN} substitutes the aryl chlorine directly is incorrect here because the solution indicates cyanohydrin formation at the carbonyl group. Focus first on nucleophilic addition to the ketone carbonyl.

  • Treating the first intermediate as unchanged cyanohydrin without following the full sequence can lead to the wrong option. Track both reagents in order and match the final product set, not only the first intermediate.

  • Ignoring that A and B are formed by two different reaction paths is a conceptual error. Read the scheme carefully and identify the product of each branch separately before selecting an option.

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