Illustrated Glossary of Organic Chemistry

Electron donating group (EDG; electron releasing group; ERG): An atom or group that release electron density to neighboring atoms from itself, usually by resonance or inductive effects.




Methyl carbocation
Less stable
  
Tert-butyl carbocation
More stable
The tert-butyl carbocation is more stable than the methyl carbocation because methyl groups release electron density via inductive effects or hyperconjugation. A methyl group is an electron donor.




Carbocation without resonance
Less stable
  
Carbocation with resonance
More stable
The carbocation with an oxonium ion resonance contributor is more stable than one without because the oxygen lone pairs are shared via resonance. This hydroxyl group is an electron donating group.