Question

In electrophilic aromatic substitution reactions, why is the the hydroxyl group an o,p-director?

Answer 1

The hydroxyl group is an electron-donating group, so it activates the ring. i.e. it donates electron density into the ring, instead of withdrawing it from the ring.

Consider the resonance structures of phenoxide. We would have:

You can see that only the 2, 4, and 6 positions can support the electron density from the hydroxyl group.

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In electrophilic aromatic substitution (EAS), benzene acts as a nucleophile upon an electrophile.

So, if you had `"Br"_2` as an electrophile, with `"FeBr"_3` as the catalyst, then the benzene ring can act as a nucleophile in the EAS mechanism as follows: