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A. Give the… (Class 12 Chemistry SQP 2024-25, Q24a)

questionbuddy.in/q/cbse-12-chemistry-2024-25-sqp-q24a-give-chemical-reaction-involved-nitrotoluene

ChemistryCBSE Class 12 · Sample paper, session 2024-25 · 3 marks · Short answer

CBSE Class 12 Chemistry sample paper 2024-25: question 24(a)

From the official CBSE sample question paper for 2024-25, section C, question 24(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q24(a) · 3 marks · Short answerAldehydes, Ketones and Carboxylic Acids

a. Give the chemical reaction involved when p-nitrotoluene undergoes Etard reaction. (1)
b. Why does Benzoic acid exist as a dimer in an aprotic solvent? (1)
c. Benzene on reaction with methylchloride in the presence of anhydrous forms toluene. What is the expected outcome if benzene is replaced by benzoic acid? Give a reason for your answer. (1)

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

Open one hint at a time and try again before the next.

Hint 1

Étard reagent is chromyl chloride. What does it convert a methyl group on the ring into?

Hint 2

The –COOH group has both an H-bond donor and an H-bond acceptor.

Hint 3

Think about how –COOH affects ring electron density and what it does to the Lewis acid AlCl₃.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (a) Étard reaction: chromyl chloride in oxidises the methyl group to a chromium complex, which is hydrolysed to the aldehyde.
    (p-nitrobenzaldehyde)

    1 mark

  2. (b) In an aprotic solvent, there is no H-bonding with the solvent. Two benzoic acid molecules therefore form two intermolecular hydrogen bonds between their –COOH groups (). This gives a cyclic dimer.

    1 mark

  3. (c) No Friedel–Crafts methylation takes place; toluic acid is not formed. The –COOH group is strongly electron-withdrawing and deactivates the ring. Also, the Lewis acid catalyst gets bonded to the carboxyl group, so it is no longer available as a catalyst.

    1 mark

Answer: (a) p-nitrotoluene → (CrO₂Cl₂/CS₂, then H₃O⁺) p-nitrobenzaldehyde; (b) intermolecular H-bonding forms a cyclic dimer; (c) no reaction: –COOH deactivates the ring and binds AlCl₃

Where the marks are

  • Étard reaction with CrO₂Cl₂ then hydrolysis giving p-nitrobenzaldehyde (1 mark)
  • Intermolecular H-bonding forming a dimer (1 mark)
  • No Friedel–Crafts reaction: deactivating –COOH and AlCl₃ bonded to the carboxyl group (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Aldehydes, Ketones and Carboxylic Acids, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.