https://doi.org/10.1351/goldbook.M04042
Representation of some
molecular entities
solely by localized two-electron two-centre bonds
appears to be unsatisfactory. Instead, multi-centre bonds have to be considered in which electron pairs occupy orbitals encompassing three or more atomic centres. Examples include the three-centre bonds in diborane, the delocalized π-bonding of benzene and bridged carbocations
.