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An organic compound… (Class 12 Chemistry SQP 2023-24, Q33a)

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ChemistryCBSE Class 12 · Sample paper, session 2023-24 · 5 marks · Long answer

CBSE Class 12 Chemistry sample paper 2023-24: question 33(a)

From the official CBSE sample question paper for 2023-24, section E, question 33(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(a) · 5 marks · Long answerAmines

An organic compound with molecular formula exists in three isomeric forms, the isomer 'A' has the highest melting point of the three. 'A' on reduction gives compound 'B' with molecular formula . 'B' on treatment with at 0-5 °C to form compound 'C'. On treating C with , it gets converted to D with formula , which on further reaction with followed by hydrolysis forms 'E' . Write the structure of compounds A to E. Write the chemical equations involved.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

C₇H₇NO₂ can be written as CH₃–C₆H₄–NO₂. Which position isomer is the most symmetrical, and so has the highest melting point?

Hint 2

Follow the sequence: reduction gives an amine, NaNO₂/HCl gives a diazonium salt, and H₃PO₂ replaces –N₂⁺ with H.

Hint 3

CrO₂Cl₂ followed by hydrolysis is the Etard reaction. What does it do to a –CH₃ group on a benzene ring?

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. Identify A. is (nitrotoluene), which has o-, m- and p-isomers. The para isomer is the most symmetrical and packs best in the crystal lattice, so it has the highest melting point.

    A = p-nitrotoluene (4-methylnitrobenzene): a benzene ring with at C-1 and at C-4.

    1 mark

  2. A → B (reduction of –NO₂ to –NH₂).

    B = p-toluidine (4-methylaniline, p-methylbenzenamine), .

    1 mark

  3. B → C (diazotisation at 273–278 K).

    C = p-methylbenzenediazonium chloride ().

    1 mark

  4. C → D (the –N₂⁺ group is replaced by H).

    D = toluene (methylbenzene), .

    1 mark

  5. D → E (Etard reaction). Chromyl chloride oxidises the group to a chromium complex, which on hydrolysis gives the aldehyde.

    E = benzaldehyde, .

    1 mark

Answer: A = p-nitrotoluene; B = p-toluidine (4-methylaniline); C = p-methylbenzenediazonium chloride; D = toluene; E = benzaldehyde

Where the marks are

  • Identifies A as p-nitrotoluene, with the reason that the symmetrical para isomer has the highest melting point (1 mark)
  • Gives B as p-toluidine with the Sn/HCl reduction equation (1 mark)
  • Gives C as p-methylbenzenediazonium chloride with the diazotisation equation at 0–5 °C (1 mark)
  • Gives D as toluene with the H₃PO₂ reduction equation (1 mark)
  • Gives E as benzaldehyde with the Etard reaction, CrO₂Cl₂ followed by hydrolysis (1 mark)

Revise the chapter

  • Chapter: Amines (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Amines, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2023-24: 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.