In aldehydes, the carbonyl group is bonded to a carbon and hydrogen, while in ketones it is bonded to two carbon atoms. The compounds in which the carbonyl group is bonded to oxygen are known as carboxylic acids and their derivatives.
The hybridization of the \(C\) in the carbonyl group is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → sp2
The carbonyl carbon is sp2-hybridised. Its three sp2 orbitals form three σ bonds (to O and to two other atoms), and the unhybridised p-orbital overlaps with a p-orbital of oxygen to form the π bond. The carbonyl carbon and the three atoms attached to it lie in one plane with bond angles of about 120° (trigonal planar).
Why the other options are incorrect
Option (1) sp — Incorrect. An sp carbon forms two σ bonds and two π bonds with a linear 180° geometry, as in C≡C or O=C=O, not in a carbonyl group bonded to two other atoms.
Option (3) sp3 — Incorrect. sp3 carbon forms four σ bonds (tetrahedral, 109.5°) and has no p-orbital left for a π bond.
Option (4) sp3d — Incorrect. Carbon has no d-orbitals in its valence shell, so it cannot use sp3d hybridisation.
NCERT (2026-27 edition):
Structure of the Carbonyl Group – “The carbonyl carbon atom is sp2-hybridised and forms three sigma (σ) bonds. The fourth valence electron of carbon remains in its p-orbital and forms a π-bond with oxygen by overlap with p-orbital of an oxygen. In addition, the oxygen atom also has two non bonding electron pairs. 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 (Figure 8.1).”
