Concept:Reactivity is context-dependent. While phenols are highly reactive toward electrophilic
aromatic ring substitution, the core functional group itself (the C-O bond) is heavily deactivated toward nucleophilic substitution compared to aliphatic alcohols.
Formula:Not applicable to this conceptual question.
Solution:- The lone pairs on the oxygen atom are delocalized into the benzene ring via resonance.
- This delocalization imparts partial double-bond character to the carbon-oxygen (C-O) bond.
- Because this C-O bond is significantly stronger and shorter than in normal alcohols, it is incredibly difficult to break via standard nucleophilic substitution (like with \(\text{PCl}_5\) or HX).
- Therefore, regarding the functional group substitution reactions typical of alcohols, phenols are generally considered less reactive.
Why other options are incorrect:Phenols are not entirely nonreactive (they can be cleaved under extreme conditions, or react readily as weak acids). They are not "more reactive" than alcohols regarding the breaking of the C-O bond.
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