Identify the product 'C' in the following sequence of reactions:

The correct answer is Option (2) → \((CH_3)_3C-OH\) (2-methylpropan-2-ol)

A ketone with a Grignard reagent always gives a tertiary alcohol. First, propan-2-ol vapour passed over heated copper at 573 K is dehydrogenated; a secondary alcohol gives a ketone, so A is acetone:

    \( \displaystyle \ce{CH3CH(OH)CH3} \xrightarrow{\ce{Cu},\ \text{573 K}} \ce{CH3COCH3 + H2} \)

Then \( \ce{CH3MgBr} \) adds to the C=O of acetone (nucleophilic addition), giving the magnesium alkoxide B:

    \( \displaystyle \ce{(CH3)2C=O + CH3MgBr -> (CH3)3C-OMgBr} \)

Hydrolysis of the adduct gives the alcohol C, tert-butyl alcohol (2-methylpropan-2-ol):

    \( \displaystyle \ce{(CH3)3C-OMgBr + H2O} \xrightarrow{\ce{H+}} \ce{(CH3)3C-OH + Mg(OH)Br} \)

Why the other options are incorrect

• Option (1) 2-methylpropene, (CH₃)₂C=CH₂ — Incorrect. This would need dehydration of C; mild \( \ce{H3O^{+}} \) hydrolysis only frees the alcohol.

• Option (3) \(CH_3-CH_2-CH_2-OH\) — Incorrect. Propan-1-ol has only three carbons; the Grignard step adds a fourth carbon.

• Option (4) 2-methylbutan-2-ol, (CH₃)₂C(OH)CH₂CH₃ — Incorrect. This would need \( \ce{C2H5MgBr} \); the reagent here is \( \ce{CH3MgBr} \).

NCERT (2026-27 edition):
Oxidation – “… When the vapours of a primary or a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and an aldehyde or a ketone is formed while tertiary alcohols undergo dehydration.”

From Grignard Reagents – “Alcohols are produced by the reaction of Grignard reagents (Unit 6, Class XII) with aldehydes and ketones. The first step of the reaction is the nucleophilic addition of Grignard reagent to the carbonyl group to form an adduct. Hydrolysis of the adduct yields an alcohol.”