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Electron deficiency (and electron-deficient) is jargon that is used in two contexts: species that violate the octet rule because they have too few valence electrons and species that happen to follow the octet rule but have electron-acceptor properties, forming donor-acceptor
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
charge-transfer salt
In chemistry, a charge-transfer (CT) complex or electron-donor-acceptor complex describes a type of supramolecular assembly of two or more molecules or ions. The assembly consists of two molecules that self-attract through electrostatic forces, ...
s.
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
Trimethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( CH3)6 (abbreviated as Al2Me6 or TMA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industriall ...
. The electron deficiency in such compounds is similar to metallic bonding.
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 chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
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