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.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1144