In chemistry, an electron-withdrawing group (EWG) is a substituent that has some of the following kinetic and

thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of the ...

implications: *with regards to

electron transfer Electron transfer (ET) occurs when an electron relocates from an atom or molecule to another such chemical entity. ET is a mechanistic description of certain kinds of redox reactions involving transfer of electrons. Electrochemical processes ar ...

, electron-withdrawing groups enhance the oxidizing power tendency of the appended species.

Tetracyanoethylene Tetracyanoethylene (TCNE) is organic compound with the formula . It is a colorless solid, although samples are often off-white. It is an important member of the cyanocarbons. Synthesis and reactions TCNE is prepared by brominating malononitri ...

is an oxidant because the alkene is appended to four cyano substituents, which are electron-withdrawing. *with regards to acid-base reactions, acids with electron-withdrawing groups species have low acid dissociation constants. For EWG's attached to benzene, this effect is described by the

Hammett equation The Hammett equation in organic chemistry describes a linear free-energy relationship relating reaction rates and equilibrium constants for many reactions involving benzoic acid derivatives with meta- and para-substituents to each other with ju ...

, which allows EWGs to be discussed quantitatively. *with regards to nucleophilic substitution reactions, electron-withdrawing groups are susceptible to attack by weak nucleophiles. For example, compared to

chlorobenzene Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses Historical The major use of chlorob ...

, chlorodinitrobenzene is susceptible to reactions that displace chloride.{{cite journal , author=J. F. Bunnett, R. M. Conner, doi=10.15227/orgsyn.040.0034, title=2,4-Dinitroiodobenzene , journal=Organic Syntheses , year=1960 , volume=40 , page=34 *electron-withdrawing substituents enhance the

Lewis acidity A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any s ...

. Relative to methyl, fluorine is a strong EWG. It follows that boron trifluoride is a stronger Lewis acid than is

trimethylborane Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl). Properties As a liquid it is colourless. The strongest line in the infrared spectrum is at 1330 cm� ...

References

Physical organic chemistry Chemical bonding