MCQEasyJEE 2024Aldehydes & Ketones

JEE Chemistry 2024 Question with Solution

Which of the following compounds can give a positive iodoform test when treated with aqueous KOH solution followed by potassium hypoiodite?

  • A

    Option 1

  • B

    Option 2

  • C

    Option 3

  • D

    Option 4

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: A compound giving a positive iodoform test must contain a methyl ketone group COCH3-COCH_3 or an alcohol that can be oxidized to it.

Find: Which option gives a positive iodoform test.

The solution states that the iodoform test identifies methyl ketones or compounds oxidizable to methyl ketones.

It further concludes:

  • Compound 1 does not satisfy the condition.
  • Compound 2 contains the required COCH3-COCH_3 group.
  • Compound 3 does not satisfy the condition.
  • Compound 4 does not satisfy the condition.

Therefore, only Compound 2 gives a positive iodoform test. The correct option is B.

Reaction-Based Explanation

Reaction scheme showing a gem-dichloro compound converted by aqueous KOH to a gem-diol, then to a ketone, which on treatment with KOI gives carboxylate and CHI3 yellow precipitate.

Given: The reaction scheme in the solution shows formation of a ketone that responds to the iodoform test.

Find: Which option matches the compound giving positive iodoform test.

From the figure, aqueous KOH converts the precursor into a carbonyl compound, and subsequent treatment with KOIKOI gives CHI3CHI_3 as yellow precipitate.

The ketone formed is of the methyl ketone type, so it gives a positive iodoform test.

Hence, the correct option is B.

Common mistakes

  • Assuming every ketone gives the iodoform test is incorrect. Only methyl ketones with the group COCH3-COCH_3, or compounds oxidizable to them, respond positively.

  • Ignoring oxidizable alcohols is a mistake. Some alcohols also give the test because they are first oxidized to methyl ketones under the reaction conditions.

  • Relying only on the answer key text can be misleading here because it conflicts with the worked solution. The solution clearly concludes that only Compound 2 is correct.

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