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Aldehydes Ketones and Carboxylic Acids question

2023 · 11 Apr · Shift 2 · Q6
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Aldehydes Ketones and Carboxylic Acids question

2023 · 11 Apr · Shift 2 · Q6

JEE MainChemistryAldehydes Ketones and Carboxylic AcidsMCQ+4 / −1
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : A solution of the product obtained by heating a mole of glycine with a mole of chlorine in presence of red phosphorous generates chiral carbon atom. Reason R : A molecule with 2 chiral carbons is always optically active. In the light of the above statements, choose the correct answer from the options given below:
  1. A
    Both A and R are true and R is the correct explanation of A
  2. B
    Both A and R are true but R is NOT the correct explanation of A
  3. C
    A is true but R is false
  4. D
    A is false but R is true
View written solutionFree

Correct answer: C

  1. Identify the reaction in Assertion A

Glycine is the simplest amino acid: \ceNH2−CH2−COOH\ce{NH2-CH2-COOH}\ceNH2−CH2−COOH

When a carboxylic acid or amino acid is heated with chlorine in presence of red phosphorus, the reaction is the Hell–Volhard–Zelinsky (HVZ) reaction, which causes α\alphaα-halogenation.

So glycine gives: \ceNH2−CH2−COOH−>[Cl2/red P, Δ]NH2−CHCl−COOH\ce{NH2-CH2-COOH ->[Cl2/red\ P,\ \Delta] NH2-CHCl-COOH}\ceNH2−CH2−COOH−>[Cl2/red P, Δ]NH2−CHCl−COOH

The product is α\alphaα-chloro glycine.

  1. Check whether the product has a chiral carbon

In the product \ceNH2−CHCl−COOH\ce{NH2-CHCl-COOH}\ceNH2−CHCl−COOH, the middle carbon is attached to four different groups:

  • \ceNH2\ce{NH2}\ceNH2
  • \ceCl\ce{Cl}\ceCl
  • \ceH\ce{H}\ceH
  • \ceCOOH\ce{COOH}\ceCOOH

Since all four substituents are different, this carbon is chiral.

Hence, Assertion A is true.

  1. Examine Reason R

Reason R says:

A molecule with 2 chiral carbons is always optically active.

This is false because a molecule with two chiral carbons can be meso, and meso compounds are optically inactive due to internal compensation.

Example: meso-tartaric acid has two chiral carbons but is optically inactive.

So, Reason R is false.

  1. Choose the correct option
  • Assertion A: True
  • Reason R: False

Therefore, the correct option is: C\boxed{\text{C}}C​

  1. Comparison with stored correct answer

Stored correct answer: C

My derived answer: C

They match.

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