Electron Deficiency

Electron deficiency occurs when a compound has too few valence electrons for the connections between atoms to be described as covalent bonds. Electron deficient bonds are often better described as 3-center-2-electron bonds. Examples of compounds that are electron deficient are the boranes.

The term electron-deficient is also used in a more general way in organic chemistry, to indicate a pi-system such as an alkene or arene that has electron-withdrawing groups attached, as found in nitrobenzene or acrylonitrile. Instead of showing the nucleated character common with simple C=C bonds, electron-deficient pi-systems may be electrophilic and susceptible to nucleophilic attack, as is seen in the Michael addition or in nucleophilic aromatic substitution.

As the most extreme form of highly localize electron deficiency one can consider the metallic bond. Electron Deficient Molecules The electron deficient molecule may be defined as a molecule in which there are not enough bonding electrons available to join all the atoms in the molecule together by normal covalent bonds [i. e., electron pair bonds). In other words, electron deficient molecules may also be defined as molecules or substance in which the atoms have more stable orbitals in the valence shell than the electrons. For example, beryllium chloride is collinear in the vapour state and polymerised in solid state in which each beryllium atom is bonded tetrahedrally to four chlorine atoms, so filling, by coordinate bond two 2p-orbitals of beryllium which were vacant in discrete molecules. Similarly, aluminium chloride also dimerizes in organic solvents. Boron hydride and halides are also electron deficient molecules.