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Chemistry · Alcohols, Ethers and Phenols

JEE Main 2024 — 27 January, Shift 2 — Question 66

The final product A , formed in the following reaction sequence is:

Question figure
  1. Option A:

    Ph−CH2−CH2−CH3\mathrm{Ph}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}

  2. Option B:
    Ph−CH−CH3                      ∣                  CH3\begin{aligned}& Ph-CH-C{{H}_{3}} \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left| {} \right. \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{3}} \\ \end{aligned}
  3. Option C:
    Ph−CH−CH3                      ∣                  CH2OH\begin{aligned}& Ph-CH-C{{H}_{3}} \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left| {} \right. \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{2}}OH \\ \end{aligned}
  4. Option D:

    Ph−CH2−CH2−CH2−OH\mathrm{Ph}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{OH}

    Correct

Answer: D

Step-by-step solution

Starting compound: Ph–CH=CH2 (styrene)

Step (i) and (ii): BH3, H2O2/OH⁻ This is hydroboration-oxidation, which adds water across the double bond in anti-Markovnikov fashion (OH on the less substituted carbon).

So, Ph–CH=CH2 → Ph–CH2–CH2OH

Step (iii): HBr Since the alcohol is now on the terminal position, no reaction occurs here with HBr directly unless further activation or transformation is done. However, this step might be indicating the next transformation.

Step (iv): Mg, ether, then HCHO / H3O⁺ This implies Grignard formation:

The OH group is not directly used to form the Grignard reagent, but likely we convert a halide into a Grignard reagent.

So from Ph–CH2–CH2OH, we react with HBr to form Ph–CH2–CH2Br.

Then Mg in ether gives the Grignard: Ph–CH2–CH2–MgBr.

Reacting this with formaldehyde (HCHO) followed by acid work-up gives an additional –CH2OH group.

Final product: Ph–CH2–CH2–CH2–OH

Correct option: D Ph–CH2–CH2–CH2–OH

Answer key and solution verified before publishing.

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Exam
JEE Main 2024
Paper
27 January, Shift 2
Subject
Chemistry
Chapter
Alcohols, Ethers and Phenols
Topic
Introduction and Preparation of Alcohols

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