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Answer the following. (Class 12 Chemistry SQP 2023-24, Q20a)

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ChemistryCBSE Class 12 · Sample paper, session 2023-24 · 2 marks · Very short answer

CBSE Class 12 Chemistry sample paper 2023-24: question 20(a)

From the official CBSE sample question paper for 2023-24, section B, question 20(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q20(a) · 2 marks · Very short answerAldehydes, Ketones and Carboxylic Acids

Answer the following.

  1. (a)

    Out of p-tolualdehyde and p-nitrobenzaldehyde, which one is more reactive towards nucleophilic addition reactions, why?

    0 marks
  2. (b)

    Write the structure of the product formed when acetone reacts with 2,4 DNP reagent.

    0 marks

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

Nucleophilic addition is easier when the carbonyl carbon is more positive.

Hint 2

Compare the electronic effects of –NO₂ and –CH₃.

Hint 3

With 2,4-DNP, the C=O becomes C=N–NH–Ar and a water molecule is lost.

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) p-Nitrobenzaldehyde is more reactive. The –NO₂ group withdraws electrons (–I, –R), making the carbonyl carbon more electron-deficient, so nucleophiles attack it more easily. In p-tolualdehyde the –CH₃ group releases electrons (+I, hyperconjugation), which lowers the electrophilicity of the carbonyl carbon.

    1 mark

  2. (b) Acetone condenses with 2,4-dinitrophenylhydrazine, losing water, to give acetone 2,4-dinitrophenylhydrazone (orange-red solid): , with the two –NO₂ groups at positions 2 and 4 of the benzene ring.

    1 mark

Answer: (a) p-Nitrobenzaldehyde; (b) (CH₃)₂C=N–NH–C₆H₃(NO₂)₂ (acetone 2,4-DNP derivative)

Where the marks are

  • Identifies p-nitrobenzaldehyde with the electron-withdrawing –NO₂ vs electron-releasing –CH₃ reason (1 mark)
  • Correct structure of acetone 2,4-dinitrophenylhydrazone (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 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.