Match List-I with List-II.
| List-I (Observation about aldehydes and ketones) | List-II (Reason) |
|---|---|
| (A) Their boiling points are higher than those of hydrocarbons and ethers of comparable molecular masses. | (I) Carbon-carbon bond cleavage during the oxidation |
| (B) Their boiling points are lower than those of alcohols of similar molecular masses. | (II) Weak molecular association arising out of dipole-dipole interactions |
| (C) Their α-hydrogen atoms are acidic. | (III) Strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base |
| (D) Oxidation of a ketone gives a mixture of carboxylic acids having fewer carbon atoms than the ketone. | (IV) Absence of intermolecular hydrogen bonding |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-II, B-IV, C-III, D-I
Each observation comes from the carbonyl group: it is polar, it withdraws electrons, and it has no O–H bond.
(A) Boiling points higher than hydrocarbons and ethers — This matches (II) Weak molecular association arising out of dipole-dipole interactions. The polar C=O groups of neighbouring molecules attract one another, which hydrocarbons and the less polar ethers cannot do as strongly.
(B) Boiling points lower than alcohols — This matches (IV) Absence of intermolecular hydrogen bonding. Aldehydes and ketones have no H attached to oxygen, so their molecules cannot hydrogen bond with one another as alcohol molecules do.
(C) Acidic α-hydrogen atoms — This matches (III) Strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base. After the proton leaves, the negative charge is spread onto the carbonyl oxygen.
(D) Ketone oxidation gives acids with fewer carbon atoms — This matches (I) Carbon-carbon bond cleavage during the oxidation. Under vigorous conditions the carbon chain breaks next to the carbonyl group, so each acid formed is smaller than the ketone.
NCERT (2026-27 edition):
8.3 Physical Properties – “The boiling points of aldehydes and ketones are higher than hydrocarbons and ethers of comparable molecular masses. It is due to weak molecular association in aldehydes and ketones arising out of the dipole-dipole interactions. Also, their boiling points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding.”
8.4 Chemical Reactions – “The acidity of α-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base.”
“Ketones are generally oxidised under vigorous conditions, i.e., strong oxidising agents and at elevated temperatures. Their oxidation involves carbon-carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.”