chem question on resonance effect
basil says title for thread is too short and i lost the text i typed out just now -.-
anyway, im studying arenes and i don't understand the resonance effect. i understand that it is due to the overlapping of p orbitals to allow electrons to be donated/withdrew from the delocalized cloud of electrons by the substituent groups. i don't get how they group the electron-withdrawing/donating groups though. according to my notes:
electron-donating: -OH, -NH2, -OCH3, and halogens
electron-withdrawing: -CHO, -NO2
and the notes says that electron-withdrawing groups are such because they have 'polar multiple bonds' o.O is that like multiple pi bonds which are polar? then why is -CHO electron-withdrawing because it only has 1 polar pi bond?
Thanks in advance!