https://doi.org/10.1351/goldbook.08789
Redistribution of electron density in a molecular entity as compared with a model assuming individual atoms in the same valence states connected by localized bonds.
Notes:
- Topological modes of the electron delocalization include:
- ribbon (one-dimensional) delocalization of \(\ce{\uppi {-}}\) or \(\ce{\upsigma {-}electrons}\) or both, which is typical of linear conjugated polymers that are therefore termed one-dimensional conductors;
- surface delocalization of \(\ce{\uppi {-}}\) or \(\ce{\upsigma {-}electrons}\) or both through an overlap of radially oriented orbitals of a cyclic molecule such as a molecule of cyclopropane or benzene;
- volume delocalization of \(\ce{\upsigma {-}electrons}\) through an overlap of \(\ce{\upsigma {-}orbitals}\) directed inside a molecular polyhedron, e.g., in tetrahedrane or carboranes.
- A delocalized electron is not associated with a particular atom or particular covalent bond but occupies an extended orbital spread over several to many atoms or the whole lattice.
- Extensive delocalization of electrons is typical of metals, semiconductors, graphite, conjugated polymers, polysilanes, boranes, conjugated compounds such as organic dyes and others.