ChemistryCBSE Class 12 · Board exam 2023, set 56/1/1 · 3 marks · Short answer

CBSE Class 12 Chemistry 2023: question 28

Set in the CBSE Class 12 board exam of 2023, paper 56/1/1, section C, question 28, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28 · 3 marks · Short answerAlcohols, Phenols and Ethers

How do you convert the following : (Any three)
(a) Phenol to picric acid
(b) Propanone to 2-Methylpropan-2-ol
(c) Phenol to anisole
(d) Propene to Propan-1-ol

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 56/1/1.

Hints

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

Hint 1

Picric acid has three –NO₂ groups on phenol; direct nitration oxidises phenol, so sulphonate first.

Hint 2

A tertiary alcohol can be made from a ketone with a Grignard reagent.

Hint 3

Anisole is an ether (Williamson synthesis); propan-1-ol needs anti-Markovnikov addition of water.

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.

(a) Phenol → picric acid: Phenol is treated with conc. H₂SO₄ to form phenol-2,4-disulphonic acid. This is then treated with conc. HNO₃, which gives 2,4,6-trinitrophenol.
$C_{6} H_{5} OH conc. H_{2} S O_{4} C_{6} H_{3} (OH) (S O_{3} H)_{2} conc. HN O_{3} C_{6} H_{2} (OH) (N O_{2})_{3}$ (picric acid)
1 mark
(b) Propanone → 2-methylpropan-2-ol: Propanone reacts with $C H_{3} MgBr$ in dry ether, and the adduct is then hydrolysed.
$(C H_{3})_{2} C = O + C H_{3} MgBr dry ether (C H_{3})_{3} C - OMgBr H_{2} O/ H^{+} (C H_{3})_{3} C - OH + Mg (OH) Br$
1 mark
(c) Phenol → anisole: Phenol is converted to sodium phenoxide with NaOH. The phenoxide is then heated with methyl iodide (Williamson synthesis).
$C_{6} H_{5} OH NaOH C_{6} H_{5} O^{-} N a^{+} C H_{3} I C_{6} H_{5} OC H_{3} + NaI$
1 mark
(d) Propene → propan-1-ol: Hydroboration–oxidation gives the anti-Markovnikov alcohol.
$C H_{3} CH = C H_{2} (B H_{3})_{2} (C H_{3} C H_{2} C H_{2})_{3} B H_{2} O_{2} /O H^{-} 3C H_{3} C H_{2} C H_{2} OH$
(Any three conversions earn the full 3 marks.)

Answer: (a) conc. H₂SO₄ then conc. HNO₃; (b) CH₃MgBr then H₂O/H⁺; (c) NaOH then CH₃I; (d) B₂H₆ then H₂O₂/OH⁻

Where the marks are

Any three correct conversions with correct reagents/equations, 1 mark each (3 marks)

Revise the chapter

Chapter: Alcohols, Phenols and Ethers (notes, formulas, where marks are lost and every past question)
Topic: Ethers: Williamson Synthesis and Cleavage

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 paper2023 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.

CBSE Class 12 Chemistry 2023: question 28

Hints

Step-by-step solution

Revise the chapter

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