MCQ Detailed View

In aldehydes and ketones, the carbonyl group (>C=O) is the defining functional group. It consists of a carbon atom double-bonded to an oxygen atom. The key feature of the carbonyl carbon is its hybridization state.

The carbon atom in the carbonyl group undergoes sp² hybridization. It forms three sigma (σ) bonds: one with the oxygen atom (in the C=O bond), one with a hydrogen atom in aldehydes or an alkyl group in ketones, and one with the remaining group attached to the carbon. These three σ bonds are arranged in a trigonal planar geometry around the carbon atom, which is characteristic of sp² hybridization with bond angles close to 120°.

In this hybridization, the carbon atom mixes one s orbital and two p orbitals to form three equivalent sp² orbitals. The unhybridized p orbital on the carbon overlaps side-by-side with a p orbital of oxygen to form the pi (π) bond of the carbon-oxygen double bond.

The oxygen atom is more electronegative than carbon, so the C=O bond is highly polarized. This makes the carbonyl carbon partially positive (δ⁺) and electrophilic, which is why it is reactive toward nucleophiles.

sp³ hybridization (tetrahedral geometry) is found in saturated carbon atoms, such as in alkanes. sp hybridization occurs in carbon atoms with linear geometry, such as in alkynes. An unhybridised carbon does not describe a valid bonding state in stable organic molecules.

The sp² hybridization of the carbonyl carbon is fundamental to understanding the reactivity and geometry of aldehydes and ketones in organic chemistry.