Logo
Jeeify
MCQMediumJEE 2023Phenols

JEE Chemistry 2023 Question with Solution

An organic compound 'A' with empirical formula C6H6OC_6H_6O gives sooty flame on burning. Its reaction with bromine solution in low polarity solvent results in high yield of B. B is:

  • A
    Phenol ring with an OH group and a bromine substituent at the para position on the benzene ring.
  • B
    Five-membered oxygen-containing ring with one double bond and a CH2CH2Br side chain attached.
  • C
    Five-membered oxygen-containing saturated ring with one bromine and one CH2CH3 substituent on adjacent carbons.
  • D
    Phenol ring with an OH group and a bromine substituent at the ortho position on the benzene ring.

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: Compound A has empirical formula C6H6OC_6H_6O and gives a sooty flame on burning.

Find: The major product B formed with bromine in a low polarity solvent.

Aromatic compounds burn with a sooty flame. So compound A is identified as phenol.

Reaction scheme showing phenol reacting with bromine in CS2 to form para-bromophenol as the major product.

In a low polarity solvent such as CS2\text{CS}_2, phenol undergoes electrophilic substitution with bromine and gives predominantly the monobrominated product. The para product is obtained in high yield.

Therefore, B is p-bromophenol, so the correct option is C.

Detailed Extraction from the solution

Given: Aromatic compounds such as phenols burn with a sooty flame due to incomplete combustion.

Find: Which structure corresponds to product B after bromination in a low polarity solvent.

Phenol reacts with bromine in the presence of a low polarity solvent like CS2\text{CS}_2 by electrophilic substitution, where bromine replaces a hydrogen atom on the benzene ring.

Phenol treated with bromine in CS2 giving para-bromophenol as the major product, with OH retained on the benzene ring.

The solution explicitly states that the correct structure for B is obtained by brominating phenol as shown in option (3). Hence, the correct option is C.

There is a discrepancy with the answer key, which says (1), but the solution is taken.

Common mistakes

  • Identifying C6H6OC_6H_6O as a non-aromatic alcohol is incorrect because the sooty flame indicates an aromatic system. First infer the aromatic nature, then identify A as phenol.

  • Assuming bromination gives tribromophenol is wrong here because the solvent is low polarity, such as CS2\text{CS}_2. In this medium, phenol mainly undergoes monobromination, not the aqueous bromine reaction.

  • Choosing the ortho product as the major product is a common error. Although phenol is ortho-para directing, the para product is formed in higher yield due to lower steric hindrance.

Practice more Phenols questions

Get unlimited AI-adaptive practice, mastery tracking, and an AI tutor that explains every step — free to start.

Start free trialMore on Phenols

Related questions