rehybridize

Rehybridize is a term used in chemistry to describe the process by which an atom changes the hybridization state of its atomic orbitals in response to changes in bonding or molecular geometry. In valence bond theory, atoms are described as using hybrid orbitals (such as sp3, sp2, or sp) to form sigma bonds. When the number or arrangement of electron domains around an atom changes, the atom can reorganize its orbitals to accommodate new bond angles and bond orders. Rehybridization may occur during chemical reactions, on reactive intermediates, or during conformational changes, and can involve a gradual or concerted shift in orbital character.

Common contexts include changes in bonding during reaction mechanisms. For example, in nucleophilic addition to a carbonyl group, the carbonyl carbon can be described as shifting from sp2 toward a more tetrahedral, sp3-like character as the carbonyl pi bond is broken and new sigma bonds form. In electrophilic aromatic substitution, the carbon under attack temporarily rehybridizes from sp2 to sp3 in the arenium ion intermediate and then reverts to sp2 to restore aromaticity. Hydrogenation of alkenes also involves rehybridization as the sp2 carbons become sp3 in the resulting alkane. Rehybridization can also accompany rearrangements where substituents migrate, reshaping the local bonding framework.

While the concept aids intuition about geometry and reactivity, exact descriptions often rely on molecular orbital theory and computational methods. Rehybridization helps explain why bond angles, lengths, and charge distributions change during chemical processes.