rehybridization

Rehybridization is the process by which an atom changes the hybridization state of its valence orbitals in response to changes in its bonding or electronic environment. In valence bond theory, atoms are described as using hybrid orbitals (such as sp3, sp2, and sp) to form sigma bonds and hold lone pairs. When the bonding situation changes—through bond formation or cleavage, resonance, or changes in charge—an atom may reorganize its set of hybrid orbitals to accommodate new bonds or electron pairs.

In practice, rehybridization is often invoked to rationalize changes in molecular geometry and bond angles along a reaction path. For example, a carbonyl carbon in aldehydes and ketones is sp2-hybridized and trigonal planar, but nucleophilic addition during a reaction can convert the carbon to a tetrahedral, sp3-hybridized center. Similarly, the formation of a pi bond can involve a shift from sp3 to sp2, while subsequent saturation can revert to sp3. Carbocation chemistry commonly features rehybridization of adjacent carbons from sp3 to sp2 to stabilize positive charge.

It is important to note that rehybridization is a simplifying model. Modern molecular orbital theory describes changes in electron distribution in a more delocalized fashion, and the concept of discrete hybridization states is an approximation that helps explain observed geometries and reactivity.

Applications of rehybridization include explaining reaction mechanisms, predicting geometry changes, and interpreting spectroscopic data in organic and inorganic chemistry.