Why are amine substituents ortho, para directing and carboxylic acid substituents m-directing?

Question

I understand it is because of resonance and whether or not the the substituent group is electron donating/withdrawing. How do u explain this further. Thanks

Answer 1

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It's to do with how many resonance forms the reaction intermediate can have. The more possible resonance forms there are, the more stable the intermediate and the more likely the reaction is to proceed. In molecules with electron donating groups, the intermediates in ortho and para substitution have four resonance forms, making them more stable than the intermediate in the meta substitution reaction, which has only three. You can see a diagram of this here:

http://en.wikipedia.org/wiki/Electrophilic_aromati...

Answer 2

look at the link, and pay particular activity to the considered electron donating and electron withdrawing communities, and what it does to electron density. That way, you want to apply good judgment to comprehend the answer.