Assertion (A): The carboxylic carbon of a carboxylic acid is less electrophilic than the carbonyl carbon of an aldehyde or a ketone.
Reason (R): In carboxylic acids, the bonds to the carboxyl carbon lie in one plane and are separated by about 120°.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are true but (R) is not the correct explanation of (A).
The carboxyl group is a carbonyl group joined to a hydroxyl group. The –OH group changes how strongly the carbon attracts a nucleophile, but not the shape around the carbon.
Assertion (A): The carboxylic carbon of a carboxylic acid is less electrophilic than the carbonyl carbon of an aldehyde or a ketone. — True. A lone pair on the oxygen of the –OH group takes part in resonance with the C=O group, so the positive charge on the carboxylic carbon is partly cancelled.
Reason (R): In carboxylic acids, the bonds to the carboxyl carbon lie in one plane and are separated by about 120°. — True. The three bonds of the carboxyl carbon are planar, about 120° apart.
Why R does not explain A?
The carbonyl carbon of aldehydes and ketones is also planar with bond angles of about 120°, so this shape cannot make the carboxylic carbon different from it.
The correct reason is the resonance shown below: the –OH oxygen shares its lone pair with the carbon and so lowers its electrophilic character.
NCERT (2026-27 edition):
8.6.2 Structure of Carboxyl Group – “In carboxylic acids, the bonds to the carboxyl carbon lie in one plane and are separated by about 120°. The carboxylic carbon is less electrophilic than carbonyl carbon because of the possible resonance structure shown below:”
8.1.2 Structure of the Carbonyl Group – “…Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the π-electron cloud is above and below this plane. The bond angles are approximately 120° as expected of a trigonal coplanar structure …”