electron withdrawing groups

[Sharon Rodriguez 3H]

What are some important/common electron withdrawing groups that we should look out for? Also could somebody further explain differences between electron withdrawing groups and electron donating groups? Thanks!

[Jessica Tejero 3L]

An electron withdrawing group draws electrons away from a reaction center. When this center is an electron rich carbanion or an alkoxide anion, the presence of the electron-withdrawing substituent has a stabilizing effect. Electron withdrawing group are atoms or groups that draw electron density from neighboring atoms towards itself.