In
chemistry, electron-rich is jargon that is used in multiple related meanings with either or both kinetic and thermodynamic implications:
*with regards to
electron-transfer, electron-rich species have low
ionization energy and/or are
reducing agent
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth me ...
s.
Tetrakis(dimethylamino)ethylene
Tetrakis(dimethylamino)ethylene (TDAE) is an organic compound with the formula (NMe2)2sub>2 (where Me = CH3). A colorless liquid, this compound is classified as an enamine. Primary and secondary enamines tend to isomerize, but tertiary enamines a ...
is an electron-rich alkene because, unlike
ethylene, it forms isolable
radical cation
In organic chemistry, a radical anion is a free radical species that carries a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a ...
. In contrast, electron-poor alkene
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 electron acceptor, forming isolable anions.
*with regards to
acid-base reactions, electron-rich species have high
pKa's and react with weak
Lewis acids.
*with regards to
nucleophilic substitution reactions, electron-rich species are relatively strong nucleophiles, as judged by rates of attack by electrophiles. For example, compared to
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
,
pyrrole is more rapidly attacked by electrophiles. Pyrrole is therefore considered to be an electron-rich aromatic ring. Similarly, benzene derivatives with electron-donating groups (EDGs) are attacked by electrophiles faster than in benzene. The electron-donating vs electron-withdrawing influence of various functional groups have been extensively parameterized in
linear free energy relationships.
*with regards to
Lewis acidity, electron-rich species are strong
Lewis bases.
[{{cite journal , doi=10.1021/ar9501479, title=Recognition of Electron-Donating Guests by Carborane-Supported Multidentate Macrocyclic Lewis Acid Hosts: Mercuracarborand Chemistry , year=1997 , last1=Hawthorne , first1=M. Frederick , last2=Zheng , first2=Zhiping , journal=Accounts of Chemical Research , volume=30 , issue=7 , pages=267–276 ]
References
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Physical organic chemistry
Chemical bonding