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JEE Chemistry 2026 Question with Solution

A student is given one compound among the following compounds that gives positive test with Tollen's reagent. The compound is:

Four cyclic ether compounds labeled A, B, C and D; A and B contain methoxy substituents, C is a cyclic hemiacetal with hydroxyl group, and D is a cyclic alcohol attached to the ring oxygen system.
  • A

    B

  • B

    A

  • C

    C

  • D

    D

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: One among compounds A, B, C, and D gives a positive test with Tollen's reagent.

Find: Which compound gives the positive Tollen's test.

Step 1: Understanding Tollen's reagent test. Tollen's reagent gives a positive test with aldehydes and compounds that can form aldehydes under the reaction conditions.

Step 2: Analysing the given compounds.

  • Compound A and B: These are acetals/ethers. Acetals do not undergo oxidation by Tollen's reagent, so they do not give a positive test.
  • Compound D: This compound is an alcohol without the ability to form an aldehyde under Tollen's test conditions, so it does not give a positive test.
  • Compound C: This compound is a hemiacetal. Hemiacetals are in equilibrium with aldehydes in aqueous medium. The aldehyde formed reacts with Tollen's reagent to produce a silver mirror.

Step 3: Conclusion. Only compound C gives a positive Tollen's test.

Therefore, the correct option is C.

Functional Group Identification

Given: The compounds differ by whether they are acetals, hemiacetals, or alcohol-containing cyclic ethers.

Find: The compound that can respond to Tollen's reagent.

The key idea is that Tollen's reagent oxidizes aldehydes. A compound will also test positive if it can generate an aldehyde in the medium.

  • Acetals are stable toward this test and do not readily open to give aldehydes under these conditions.
  • Hemiacetals are in equilibrium with the corresponding aldehyde in aqueous medium.
  • A simple alcohol does not satisfy this condition.

From the given structures, compound C is the hemiacetal, so it can generate an aldehyde and hence gives the positive Tollen's test.

Therefore, the correct option is C.

Common mistakes

  • Mistake: Treating acetals and hemiacetals as chemically equivalent. Why it is wrong: acetals do not readily furnish aldehydes under Tollen's test conditions, whereas hemiacetals can exist in equilibrium with aldehydes. What to do instead: identify whether the carbon bears one −OR-OR and one −OH-OH group, which indicates a hemiacetal.

  • Mistake: Assuming any compound containing oxygen will respond to Tollen's reagent. Why it is wrong: the test is specific to aldehydes or compounds that generate aldehydes. What to do instead: check for aldehyde functionality or a functional group such as a hemiacetal that can convert into an aldehyde.

  • Mistake: Selecting the alcohol-containing structure D because alcohols are oxidizable. Why it is wrong: ordinary alcohols do not necessarily give Tollen's test; the reagent is not a general test for all oxidizable alcohols. What to do instead: focus on aldehyde-forming ability, not merely the presence of an −OH-OH group.

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