Explain why nucleophilic substitution reactions are not very common in phenols.
The –OH group in phenol is directly attached to the sp2 hybridized carbon atom of the benzene ring. Due to the resonance, the carbon-oxygen bond length in phenol is smaller and therefore, is difficult to break this bond.
Due to the resonance, the ortho- and para-positions in the benzene ring becomes electron-rich and therefore, activates it towards electrophilic substitution reaction. Thus, nucleophilic substitution reactions are not very common in phenols.
The resonance structures in phenol:
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