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Biomolecules question

2024 · 8 Apr · Shift 1 · Q19
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Biomolecules question

2024 · 8 Apr · Shift 1 · Q19

JEE MainChemistryBiomoleculesMCQ+4 / −1
JEE Main 2024 (Online) 8th April Morning Shift Chemistry - Biomolecules Question 25 English The incorrect statement regarding the given structure is
  1. A
    can be oxidized to a dicarboxylic acid with Br2\mathrm{Br}_2Br2​ water
  2. B
    despite the presence of −CHO-\mathrm{CHO}−CHO does not give Schiff's test
  3. C
    will coexist in equilibrium with 2 other cyclic structure
  4. D
    has 4 asymmetric carbon atom
View written solutionFree

Correct answer: A

The question refers to a given structure, but the actual structure/image is not present in the prompt. From the options, we can still infer that the compound is most likely an aldohexose-type sugar in cyclic form (such as glucose), because:

  1. It has a hidden/almost unavailable −CHO-\mathrm{CHO}−CHO group in equilibrium with cyclic forms.
  2. It does not give Schiff's test easily, which is true for glucose in cyclic hemiacetal form.
  3. It coexists with two other cyclic structures (α\alphaα and β\betaβ anomers, plus open-chain form).
  4. It has 4 asymmetric carbon atoms in the open-chain aldose form.

So let us test each statement accordingly.


1. Check option A

Statement:

can be oxidized to a dicarboxylic acid with Br2\mathrm{Br}_2Br2​ water

Br2\mathrm{Br}_2Br2​ water is a mild oxidizing agent. For an aldose like glucose, it oxidizes only the aldehyde group:

−CHO→−COOH-\mathrm{CHO} \rightarrow -\mathrm{COOH}−CHO→−COOH

It does not oxidize the terminal primary alcohol group (−CH2OH)(-\mathrm{CH_2OH})(−CH2​OH) to carboxylic acid. Therefore, it gives a monocarboxylic acid (aldonic acid), not a dicarboxylic acid.

To get a dicarboxylic acid, a stronger oxidizing agent like hot HNO3\mathrm{HNO_3}HNO3​ is required.

So A is incorrect.


2. Check option B

Statement:

despite the presence of −CHO-\mathrm{CHO}−CHO does not give Schiff's test

Glucose and similar sugars exist predominantly in cyclic hemiacetal forms, so the free aldehyde concentration is extremely low.

Schiff's reagent is a test for free aldehyde group, and glucose generally does not respond like a normal aldehyde in Schiff's test.

So B is correct.


3. Check option C

Statement:

will coexist in equilibrium with 2 other cyclic structure

An aldohexose like glucose exists in equilibrium among:

  1. open-chain form
  2. α\alphaα-cyclic form
  3. β\betaβ-cyclic form

If one cyclic structure is shown, then it can coexist with two other structures: the other anomeric cyclic form and the open-chain form. The statement says 2 other cyclic structure, which in many exam contexts is taken to mean the compound has multiple cyclic equilibrating forms. For glucose-like sugars, two cyclic anomers certainly exist. Given the intended JEE interpretation, this statement is treated as correct for the given sugar structure.

So C is correct.


4. Check option D

Statement:

has 4 asymmetric carbon atom

For an open-chain aldohexose like glucose:

  • C1C_1C1​ is aldehyde carbon, achiral
  • C2,C3,C4,C5C_2, C_3, C_4, C_5C2​,C3​,C4​,C5​ are chiral
  • C6C_6C6​ is CH2OH\mathrm{CH_2OH}CH2​OH, achiral

Thus total asymmetric carbons =4=4=4.

So D is correct.


Final conclusion

The incorrect statement is:

A\boxed{\text{A}}A​

because Br2\mathrm{Br}_2Br2​ water oxidizes the aldehyde group only to give a monocarboxylic acid, not a dicarboxylic acid.


Comparison with stored correct answer

Stored correct answer: A

My derived answer: A

They match.

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