How can O- and COO- act as an electron releasing group in a π system?

[Frigus]

can anyone explain me how O negative and COO negative acts as electron releasing group,I understood how alkyl groups acts as electron releasing group but I can't understand this

 

[TeethWhitener]

Are you referring to activation/deactivation of aromatics? It might help to write out the possible resonance structures. At any rate, for both species, there is a large electron density on the functional group that can form a somewhat continuous connection with the conjugated pi system of the aromatic group.

 

[KevinMcHugh]

Through resonance of the pi orbitals. Sometimes resonance is more important than electronegativity.