In chemistry, electron deficiency (and electron-deficient) is jargon that is used in two contexts: chemical species that violate the

octet rule The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The ru ...

because they have too few valence electrons and species that happen to follow the octet rule but have electron-acceptor properties, forming donor-acceptor charge-transfer salts.

Octet rule violations

left, 144px Traditionally, "electron-deficiency" is used as a general descriptor for boron hydrides and other molecules which do not have enough valence electrons to form localized (2-centre 2-electron) bonds joining all atoms. For example, diborane (B₂H₆) would require a minimum of 7 localized bonds with 14 electrons to join all 8 atoms, but there are only 12 valence electrons. A similar situation exists in trimethylaluminium. The electron deficiency in such compounds is similar to

metallic bonding Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be desc ...

Electron-acceptor molecules

Alternatively, electron-deficiency describes molecules or ions that function as electron acceptors. Such electron-deficient species obey the octet rule, but they have (usually mild) oxidizing properties. 1,3,5-Trinitrobenzene and related polynitrated

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

compounds are often described as electron-deficient. Electron deficiency can be measured by

linear free-energy relationship In physical organic chemistry, a free-energy relationship or Gibbs energy relation relates the logarithm of a reaction rate constant or equilibrium constant for one series of chemical reactions with the logarithm of the rate or equilibrium consta ...

s: "a strongly negative ρ value indicates a large electron demand at the reaction center, from which it may be concluded that a highly electron-deficient center, perhaps an incipient carbocation, is involved."

References

{{DEFAULTSORT:Electron Deficiency Chemical bonding