Electron donating groups - acidity/basicity confusion

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Report Thread starter 2 years ago
I'm currently a bit puzzled by certain electron donating groups (with respect to aromatic molecules) and their affect on acidity/basicity.

Take phenol for example - I understand that its -OH group is electron donating. My study guide says that electron donating groups decrease acidity by destabilising anions, hence making the conjugate base stronger. However, the phenoxide anion is stabilised by the donation of a lone pair of electrons into the aromatic ring. This seems to increase acidity because the conjugate base is weaker.

Another example - NH2 (amine) group donates electrons in the same way when it is attached to a benzene ring. Again, the anion is resonance stabilised and hence, weaker.

So why does my guide state that electron donating groups destabilise anions, making them stronger conjugate bases (and hence weaker acids)? This info is specifically given in the section about aromatic hydrocarbons. Any help would be much appreciated

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