Aldol condensation reaction is not given by:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 2,2-Dimethyl butane
Aldol condensation is given by aldehydes and ketones that have at least one α-hydrogen. In dilute alkali the α-hydrogen is removed, and the carbanion formed adds to the carbonyl group of a second molecule to give a β-hydroxy aldehyde or ketone (aldol). On heating, the aldol loses water to give an α,β-unsaturated carbonyl compound.
Option (1) Ethanal — Gives aldol condensation. \( \ce{CH3CHO} \) has three α-hydrogens. Two molecules give 3-hydroxybutanal (aldol), which loses water on heating to form but-2-enal.
\( \ce{2CH3CHO} \xrightarrow{\text{dil. NaOH}} \underset{\text{3-hydroxybutanal}}{\ce{CH3CH(OH)CH2CHO}} \xrightarrow[-\ce{H2O}]{\Delta} \underset{\text{but-2-enal}}{\ce{CH3CH=CHCHO}} \)
Option (2) Butanal — Gives aldol condensation. \( \ce{CH3CH2CH2CHO} \) has two α-hydrogens on C-2, so it forms an aldol in dilute alkali.
Option (3) 3-Methyl butanal — Gives aldol condensation. \( \ce{(CH3)2CHCH2CHO} \) also has two α-hydrogens on C-2, so it undergoes aldol condensation.
Option (4) 2,2-Dimethyl butane — Does not give aldol condensation. \( \ce{CH3C(CH3)2CH2CH3} \) is an alkane. It has no carbonyl group, so it has no acidic α-hydrogen and no C=O group for a carbanion to add to.
NCERT (2026-27 edition):
Reactions due to α-Hydrogen – …
