[cshipman]

p-Nitrophenol is brominated more slowly than phenol.  WHY???

[hobobot]

What have you tried so far? What properties of nitro groups are you familiar with?

[cshipman]

I think I may have figured it out - part of it at least - but I can't seem to put the pieces together.

I know that P-nitrophenol is a much stronger acid than phenol. The N in the nitro group has a positive formal charge (strongly electron-withdrawing) leading to an inductive effect. I also know that the negative charge on the O is de-localized by resonance. I THINK this has something to do with why p-Nitrophenol brominates more slowly, but I'm not quite sure...

[Jorriss]

Remember, [almost] all the reactions you're doing are ELECTROPHILIC aromatic addition. You are adding substituents which want more electrons. The hydroxyl group on adds electrons to the ring through resonance, so that the ring has even more electrons to donate!

What does a nitro group do to the electrons in the ring though?

[cshipman]

The nitro group has a strong tendency to pull electrons from the aromatic ring, deactivating it I think...

[Jorriss]

Right.

So you're trying to add a bromine to the ring and that bromine wants electrons. But your nitro group is taking those electrons away.

This can be supported through resonance structures of the intermediates formed.

[cshipman]

So THAT is why p-nitrophenol is brominated more slowly?

[Jorriss]

That'd be my interpretation.

[cshipman]

you're the best! Thank you :-)