Due to resonance in phenol (C₆H₅OH), the C-O bond in phenols acquire a partial double bond character. Therefore the C-O bond in phenols is stronger than the C-O single bond in aliphatic alcohols (R-OH, where R is an alkyl group). Consequently it becomes difficult to break the C-O bond in phenols. So, arylhalides can not be prepared by reaction of phenol with HCl in the presence of ZnCl₂.

Resonance in phenol