MCQ Detailed View

The carbonyl group (C=O) is the defining feature of aldehydes and ketones. In this group, the carbon atom is bonded to an oxygen atom by a double bond and to two other atoms or groups, depending on whether it is an aldehyde or a ketone. The hybridization of this carbon atom determines the geometry and reactivity of the carbonyl group. The carbon of the carbonyl group is sp² hybridised.

In sp² hybridization, the carbon atom mixes one s orbital and two p orbitals to form three sp² hybrid orbitals arranged in a trigonal planar geometry. These orbitals form sigma bonds with two substituents and one oxygen atom. The remaining unhybridized p orbital overlaps with a p orbital of oxygen to form the pi bond of the carbonyl double bond. As a result, the carbonyl carbon is trigonal planar with bond angles close to 120°.

The sp² hybridization explains the high reactivity of carbonyl compounds. The carbonyl carbon is electrophilic because oxygen is more electronegative and pulls electron density toward itself, leaving the carbon atom electron-deficient. This makes it highly susceptible to nucleophilic attack, a key reaction type in aldehydes and ketones.

The other options represent incorrect hybridizations for this group. If the carbon were sp³ hybridised, the geometry would be tetrahedral with bond angles around 109.5°, which does not fit the observed structure. sp hybridisation corresponds to linear geometry with 180° bond angles, which is not found in carbonyl compounds. An unhybridised state does not describe the bonding properly and is not possible for this structure.

Therefore, the carbon atom in the carbonyl group of aldehydes and ketones is sp² hybridised, giving the group its planar structure and unique reactivity in organic chemistry.