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Give the structure of the… (Class 12 Chemistry 2024, Q23)

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ChemistryCBSE Class 12 · Board exam 2024, set 56/5/1 · 3 marks · Short answer

CBSE Class 12 Chemistry 2024: question 23

Set in the CBSE Class 12 board exam of 2024, paper 56/5/1, section C, question 23, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q23 · 3 marks · Short answerAlcohols, Phenols and Ethers

Give the structure of the major product expected from the following reactions :

  1. (a)

    Reaction of Ethanal with methyl-magnesium bromide followed by hydrolysis.

    1 mark
  2. (b)

    Hydration of But-1-ene in the presence of dilute sulphuric acid.

    1 mark
  3. (c)

    Reaction of phenol with bromine water.

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 56/5/1.

Hints

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

Hint 1

Grignard reagent with an aldehyde other than HCHO gives a 2° alcohol.

Hint 2

For hydration, remember Markovnikov's rule; in aqueous bromine, –OH strongly activates the 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. (a) adds to the C=O of ethanal and hydrolysis then gives a secondary alcohol:
    (propan-2-ol)

    1 mark

  2. (b) Acid-catalysed hydration follows Markovnikov's rule:
    (butan-2-ol)

    1 mark

  3. (c) Bromine water brominates all the ortho and para positions, giving a white precipitate of 2,4,6-tribromophenol (benzene ring with –OH at C-1 and Br at C-2, C-4, C-6):

    1 mark

Answer: (a) ; (b) ; (c) 2,4,6-tribromophenol

Where the marks are

  • Propan-2-ol structure (1 mark)
  • Butan-2-ol structure (1 mark)
  • 2,4,6-Tribromophenol structure (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Alcohols, Phenols and Ethers, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 56/5/1: 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.