Which of the following compounds will give a ketone on oxidation with chromic anhydride (CrO_3) ? (A) (CH_3)_2CH-CH_2OH (B) CH_3CH_2CH_2OH (C) (CH_3)_3C-OH (D) CH_3-CH_2-CH(OH)-CH_3

ChemistryCBSE Class 12 · Board exam 2024, set 56/1/1 · 1 mark · MCQ

CBSE Class 12 Chemistry 2024: question 2

Set in the CBSE Class 12 board exam of 2024, paper 56/1/1, section A, question 2, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q2 · 1 mark · MCQAlcohols, Phenols and Ethers

Which of the following compounds will give a ketone on oxidation with chromic anhydride ( $Cr O_{3}$ ) ?

(A) $(C H_{3})_{2} CH - C H_{2} OH$
(B) $C H_{3} C H_{2} C H_{2} OH$
(C) $(C H_{3})_{3} C - OH$
(D) $C H_{3} - C H_{2} - CH (OH) - C H_{3}$

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

Hints

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

Hint 1

Classify each alcohol as 1°, 2° or 3°.

Hint 2

Which class of alcohol gives a ketone on oxidation?

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.

Only secondary alcohols are oxidised to ketones. Primary alcohols give aldehydes, and tertiary alcohols resist oxidation.
Butan-2-ol, $C H_{3} C H_{2} CH (OH) C H_{3}$ , is secondary, so CrO $_{3}$ oxidises it to butan-2-one.
1 mark

Answer: Option (D)

Where the marks are

Recognises that the secondary alcohol gives a ketone (1 mark)

Revise the chapter

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

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 56/1/1: every question, by section.

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CBSE Class 12 Chemistry 2024: question 2

Hints

Step-by-step solution

Revise the chapter

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