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Answer the following. (Class 12 Chemistry 2025, Q27)

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ChemistryCBSE Class 12 · Board exam 2025, set 56/1/1 · 3 marks · Short answer

CBSE Class 12 Chemistry 2025: question 27

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section C, question 27, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27 · 3 marks · Short answerAmines

Answer the following.

  1. (a)

    Arrange the following compounds in increasing order of their boiling point : , , .

    1 mark
  2. (b)

    Give plausible explanation for each of the following :
    (i) Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis.
    (ii) Amides are less basic than amines.

    2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 56/1/1.

Hints

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

Hint 1

Compare the extent and strength of hydrogen bonding in each compound.

Hint 2

Gabriel synthesis needs the halide to undergo nucleophilic substitution. Do aryl halides do that?

Hint 3

What does the neighbouring C=O group do to the nitrogen lone pair?

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) . A 2° amine has only one N–H and forms weaker hydrogen bonds than a 1° amine. O–H forms stronger hydrogen bonds than N–H because O is more electronegative.

    1 mark

  2. (b)(i) Aryl halides do not undergo nucleophilic substitution with the phthalimide anion, because the C–X bond has partial double bond character. So aromatic primary amines cannot be made by this route.

    1 mark

  3. (b)(ii) In amides the lone pair on N is delocalised onto the carbonyl oxygen by resonance (). The lone pair is therefore less available for donation to a proton, so amides are less basic than amines.

    1 mark

Answer: (a) (CH₃)₂NH < CH₃CH₂NH₂ < CH₃CH₂OH; (b)(i) aryl halides do not undergo SN with phthalimide anion; (ii) resonance with C=O reduces N lone pair availability

Where the marks are

  • Correct boiling point order (1 mark)
  • Aryl halides do not react with the phthalimide anion by nucleophilic substitution (1 mark)
  • Lone pair on N delocalised by resonance with C=O (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 paper2025 board paper, set 56/1/1: 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.