Read the Passage carefully and answer the questions.
The carbonyl group of aldehydes and ketones is highly polar. The positively charged carbon is readily attacked by electron-rich nucleophile and the negatively charged oxygen atom is attacked by an electro-deficient electrophile. Aldehydes and ketones undergo nucleophilic addition reactions in the presence of acid or a base. The mechanism involves attack of a nucleophile on the electron deficient carbonyl carbon to form a tetrahedral intermediate. A new bond is formed between the carbon and oxygen. Protonation of the anion furnished by the reaction medium yields a neutral addition product. The addition product is same whether the reaction is catalyzed by acid or a base. For example in the presence of base aldehydes and ketones react with hydrogen cyanide to form cyanohydrin.
What is the product formed when an aldehyde other than formaldehyde is treated with Grignard reagent?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Secondary alcohol
A Grignard reagent, R′MgX, behaves as a source of the carbanion R′\( \ce{^{-}} \). It adds to the carbonyl carbon in a nucleophilic addition, and the adduct is then hydrolysed to an alcohol. Methanal gives a primary alcohol, other aldehydes a secondary alcohol, and ketones a tertiary alcohol.
For an aldehyde other than formaldehyde:
\( \displaystyle \ce{R-CHO + R'MgX -> R-CH(R')-OMgX} \)
\( \displaystyle \ce{R-CH(R')-OMgX + H2O -> R-CH(OH)-R' + Mg(OH)X} \)
For example, ethanal and methylmagnesium bromide give propan-2-ol. The carbon carrying the OH group is bonded to two carbon atoms, so the product is a secondary alcohol.
Why the other options are incorrect
Option (1) Carboxylic acid — Incorrect. A Grignard reagent gives a carboxylic acid when it adds to carbon dioxide (dry ice), followed by hydrolysis, not to an aldehyde.
Option (2) Primary alcohol — Incorrect. Only methanal gives a primary alcohol, because its carbonyl carbon carries two H atoms.
Option (4) Tertiary alcohol — Incorrect. A tertiary alcohol is obtained from a ketone, whose carbonyl carbon already has two R groups.
NCERT (2026-27 edition):
From Grignard Reagents
