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How do you convert : (3 ×… (Class 12 Chemistry 2025, Q26B)

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

CBSE Class 12 Chemistry 2025: question 26(B)

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section C, question 26(B), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26(B) · 3 marks · Short answerHaloalkanes and Haloarenes

How do you convert : (3 × 1 = 3)
(a) Chlorobenzene to biphenyl
(b) Propene to 1-Iodopropane
(c) 2-bromobutane to but-2-ene.

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

Joining two aryl groups using sodium is a named reaction.

Hint 2

To put a halogen on the terminal carbon of propene, use the peroxide effect, then swap Br for I.

Hint 3

Removing HBr from an alkyl halide needs a strong base in alcohol; apply Saytzeff's rule.

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) Fittig reaction, heating chlorobenzene with sodium in dry ether:

    1 mark

  2. (b) Anti-Markovnikov addition of HBr in the presence of peroxide, then the Finkelstein reaction:

    1 mark

  3. (c) Dehydrohalogenation with alcoholic KOH on heating; by Saytzeff's rule the more substituted alkene is the major product:

    1 mark

Answer: (a) Fittig reaction with Na/dry ether; (b) HBr/peroxide, then NaI/acetone; (c) alcoholic KOH, heat

Where the marks are

  • Fittig reaction giving biphenyl (1 mark)
  • Peroxide HBr addition followed by Finkelstein reaction (1 mark)
  • Elimination with alcoholic KOH giving but-2-ene (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Haloalkanes and Haloarenes, 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.