Consider the following statements about the polarity and electrophilic character of carbonyl compounds.
(A) The carbon–oxygen double bond of the carbonyl group is polarised due to the higher electronegativity of oxygen relative to carbon.
(B) The carbonyl carbon is a nucleophilic (Lewis base) centre and the carbonyl oxygen is an electrophilic (Lewis acid) centre.
(C) The high polarity of the carbonyl group is explained on the basis of resonance involving a neutral structure and a dipolar structure.
(D) The polarity of the carbonyl group is reduced in benzaldehyde due to resonance, so benzaldehyde is less reactive than propanal in nucleophilic addition reactions.
(E) The carboxylic carbon of a carboxylic acid is more electrophilic than the carbonyl carbon of aldehydes and ketones because of resonance.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B) and (E) only
Oxygen pulls the shared electrons of the C=O bond towards itself, so the carbonyl carbon carries a partial positive charge and the oxygen a partial negative charge. Anything that feeds electrons to the carbonyl carbon, such as resonance with a benzene ring or with the OH group of an acid, makes it less electrophilic.
(A) The carbon–oxygen double bond of the carbonyl group is polarised due to the higher electronegativity of oxygen relative to carbon. — Correct statement. This is the origin of the polarity of the carbonyl group.
(B) The carbonyl carbon is a nucleophilic (Lewis base) centre and the carbonyl oxygen is an electrophilic (Lewis acid) centre. — Incorrect statement. The roles are the other way round: the electron-poor carbon is the electrophilic (Lewis acid) centre and the oxygen, with its lone pairs, is the nucleophilic (Lewis base) centre.
(C) The high polarity of the carbonyl group is explained on the basis of resonance involving a neutral structure and a dipolar structure. — Correct statement. The two structures are the neutral C=O form and the dipolar C+–O− form.
(D) The polarity of the carbonyl group is reduced in benzaldehyde due to resonance, so benzaldehyde is less reactive than propanal in nucleophilic addition reactions. — Correct statement. The benzene ring shares its π electrons with the carbonyl group, so the carbonyl carbon of benzaldehyde is less electrophilic than that of propanal.
(E) The carboxylic carbon of a carboxylic acid is more electrophilic than the carbonyl carbon of aldehydes and ketones because of resonance. — Incorrect statement. Resonance with the lone pair of the OH oxygen feeds electrons to the carboxylic carbon, so it is less electrophilic than the carbonyl carbon.
NCERT (2026-27 edition):
8.1.2 Structure of the Carbonyl Group – “The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. … The high polarity of the carbonyl group is explained on the basis of resonance involving a neutral (A) and a dipolar (B) structures…”
8.4 Chemical Reactions – “The carbon atom of the carbonyl group of benzaldehyde is less electrophilic than carbon atom of the carbonyl group present in propanal. The polarity of the carbonyl group is reduced in benzaldehyde due to resonance… and hence it is less reactive than propanal.”
8.6.2 Structure of Carboxyl Group – “…The carboxylic carbon is less electrophilic than carbonyl carbon because of the possible resonance structure…”