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JEE Main 2025 Jan 23 Shift 1, Chemistry Q7: Carbohydrates

JEE Main2025Jan 23, Shift 1Chemistry
Q.

Given below are two statements:

Statement I: Fructose does not contain an aldehydic group but still reduces Tollen's reagent

Statement II: In the presence of base, fructose undergoes rearrangement to give glucose.

In the light of the above statements, choose the correct answer from the options given below

  1. A

    Statement I is false but Statement II is true

  2. B

    Both Statement I and Statement II are true

  3. C

    Both Statement I and Statement II are false

  4. D

    Statement I is true but Statement II is false

Solution

Fructose is a ketohexose, so it has no group of its own. Yet it gives a positive Tollens test.

The reason is that under basic conditions (Tollens reagent is alkaline), fructose tautomerises through a common enediol intermediate to give glucose (and mannose). This is the Lobry de Bruyn-van Ekenstein rearrangement.

The aldose forms produced then reduce to silver mirror. So both statements describe what actually happens, and Statement II provides the mechanistic reason for Statement I.

Both statements are true.

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