Question: 57: Given below are two statements :
Statement 1 : The boiling points of aldehydes and ketones are higher than hydrocarbons of comparable molecular masses because of weak molecular association in aldehydes and ketones due to dipole – dipole interactions.
Statement II: The boiling points of aldehydes and ketones are lower than the alcohols of similar molecular masses due to the absence of H-bonding.
In the light of the above statements, choose the most appropriate answer from the given below
(1) Statement I is correct but Statement II is incorrect
(2) Statement I is incorrect but Statement II is correct
(3) Both Statement I and Statement II are correct
(4) Both Statement I and Statement II are incorrect
Answer: Option (3)
Explanation:
Aldehydes and ketones contain the polar carbonyl group,
which results in dipole–dipole interactions between their molecules.
These intermolecular forces are stronger than the weak London dispersion forces present in hydrocarbons of similar molecular masses.
Due to these dipole–dipole attractions, aldehydes and ketones have higher boiling points than corresponding hydrocarbons.
Alcohols, on the other hand, contain the hydroxyl group which is capable of forming strong intermolecular hydrogen bonding.
Hydrogen bonding is stronger than dipole–dipole interactions present in aldehydes and ketones.
As a result, alcohols of similar molecular masses have higher boiling points compared to aldehydes and ketones.
Therefore, both Statement I and Statement II are correct.