Question

Explain how does the −OH group attached to a carbon of benzene ring activate it towards electrophilic substitution?

Answer 1

Phenol is considered to be a resonance hybrid of the following structures:

The +R effect of the –OH group increases the electron density on the benzene ring, which makes the attack of the electrophile easier. Hence, the presence of the –OH group activates the benzene ring towards electrophilic substitution reactions. Since the electron density at the ortho and para positions is relatively high, electrophilic substitution is mainly more at the ortho and para positions.