Read the following passage given below and answer the question.
Aldehydes and ketones undergo nucleophilic addition reactions. A nucleophile attacks the electrophilic carbon atom of polar carbonyl group from perpendicular to plane of \(sp^2\) hybridized orbitals of carbonyl carbon. The hybridization of carbon changes from \(sp^2\) to \(sp^3\) and a tetrahedral alkoxide intermediate is formed. This captures \(H^+\) to give neutral product. In carboxylic acids, carbonyl carbon is less electrophilic than carbonyl carbon of aldehydes and ketones.
The correct order of reactivity for addition reaction of following carbonyl compounds with \(C_2H_5MgI\) is
(I) Methanal
(II) Propan-2-one
(III) Ethanal
(IV) 2,2,4,4-Tetramethylpentan-3-one
Choose the correct answer from the option given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → I > III > II > IV
Addition of \( \ce{C2H5MgI} \) is a nucleophilic addition to the C=O group, so reactivity falls as the carbonyl carbon becomes more crowded and less electrophilic (each alkyl group pushes electrons towards it):
(I) Methanal, HCHO — two H atoms, no alkyl group: most reactive.
(III) Ethanal, CH3CHO — one methyl group: an aldehyde, more reactive than any ketone.
(II) Propan-2-one, (CH3)2CO — two methyl groups: a ketone, less reactive.
(IV) 2,2,4,4-Tetramethylpentan-3-one, (CH3)3C–CO–C(CH3)3 — two bulky tert-butyl groups shield the carbonyl carbon: least reactive.
NCERT (2026-27 edition):
Reactivity
