Electron-rich

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 agents.^[1] Tetrakis(dimethylamino)ethylene is an electron-rich alkene because, unlike ethylene, it forms isolable radical cation.^[2] In contrast, electron-poor alkene tetracyanoethylene is an electron acceptor, forming isolable anions.^[3]
• with regards to acid-base reactions, electron-rich species have high pKa's and react with weak Lewis acids.^[4]
• 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, pyrrole is more rapidly attacked by electrophiles. Pyrrole is therefore considered to be an electron-rich aromatic ring.^[5] Similarly, benzene derivatives with electron-donating groups (EDGs) are attacked by electrophiles faster than in benzene.^[6] 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.^[7]

See also

• Electron-withdrawing group

References

1. Rosokha, Sergiy V.; Kochi, Jay K. (2008). "Fresh Look at Electron-Transfer Mechanisms via the Donor/Acceptor Bindings in the Critical Encounter Complex". Accounts of Chemical Research. 41 (5): 641–653. doi:10.1021/ar700256a. PMID 18380446.
2. Lappert, Michael F. (1988). "The Coordination Chemistry of Electron-Rich Alkenes (Enetetramines)". Journal of Organometallic Chemistry. 358 (1–3): 185–213. doi:10.1016/0022-328X(88)87079-7.
3. Stalder, Romain; Mei, Jianguo; Graham, Kenneth R.; Estrada, Leandro A.; Reynolds, John R. (2014). "Isoindigo, a Versatile Electron-Deficient Unit for High-Performance Organic Electronics". Chemistry of Materials. 26: 664–678. doi:10.1021/cm402219v.
4. Buß, Florenz; Mehlmann, Paul; Mück-Lichtenfeld, Christian; Bergander, Klaus; Dielmann, Fabian (2016). "Reversible Carbon Dioxide Binding by Simple Lewis Base Adducts with Electron-Rich Phosphines". Journal of the American Chemical Society. 138 (6): 1840–1843. doi:10.1021/jacs.5b13116. PMID 26824487.
5. Davies, Huw M. L.; Hedley, Simon J. (2007). "Intermolecular Reactions of Electron-Rich heterocycles with Copper and Rhodium Carbenoids". Chemical Society Reviews. 36 (7): 1109–1119. doi:10.1039/b607983k. PMID 17576478.
6. Lindsay Smith, J. R.; McKeer, L. C.; Taylor, J. M. "4-Chlorination of Electron-Rich Benzenoid Compounds: 2,4-Dichloromethoxybenzene". Organic Syntheses. 67: 222. doi:10.15227/orgsyn.067.0222; Collected Volumes, vol. 8, p. 167.
7. Hawthorne, M. Frederick; Zheng, Zhiping (1997). "Recognition of Electron-Donating Guests by Carborane-Supported Multidentate Macrocyclic Lewis Acid Hosts: Mercuracarborand Chemistry". Accounts of Chemical Research. 30 (7): 267–276. doi:10.1021/ar9501479.