Carbonyl groups

Similar theory describes the bonding in a carbonyl group (C=O) in which both the carbon and oxygen atoms are sp² hybridized. The subsequent energy level diagram displays how the valence electrons of oxygen are set after sp² hybridization. Two of the sp² hybridized orbitals are filled along with lone pairs of electrons that leave two half-filled orbitals obtainable for bonding. The sp² orbital can be employed to create a strong σ bond, whereas the 2p_y orbital can be employed for the weaker π bond. Figure displays how the σ and π bonds are created in the carbonyl group and describes why carbonyl groups are planar with the carbon atom comprising a trigonal planar shape. It also describes the reactivity of carbonyl groups because the π bond is weaker as compared to the σ bond and is more likely to be included in reactions.

Figure: Energy level diagram for sp2 hybridized oxygen.

Figure: (a) Formation of the carbonyl σ bond; (b) formation of the carbonyl π bond.