Phenols, although, are weak acids, yet these are stronger acids than alcohols.
This can be explained on the basis of the following facts :
(i) Phenol exists as a resonance hybrid of the following structures.
Resonating structures of phenol (note that the structures III to V involve charge separation and hence are less stable).
Thus due to resonance, oxygen atom of the OH group acquires a positive charge (see structures III to V) and hence attracts electrons pair of the O-H bond leading to the release of hydrogen atom as proton.
Since resonance is impossible in alcohols (due to absence of conjugation of the lone electron pair of oxygen with a double bond), the hydrogen atom is more firmly linked to the oxygen atom and hence alcohols are neutral in nature.
(ii) Once the phenoxide ion is formed, it stabilises itself by resonance, actually phenoxide ion is more stable than the parent phenol.
Resonating structures of phenoxide ion (note that all structures are similar and hence equally stable)
Note that all resonating structures of the phenoxide ion have a negative charge, hence these are almost equally stable; while I and II resonating structures of phenol have no charge hence these are more stable than structures III to V having both positive and negative charges.
Thus phenoxide ion is more resonance stabilised than phenol. Since there is no possibility for the delocalisation of negative charge in the alkoxide ion,, the latter is not stable and hence alcohols have practically no tendency to ionise to form alkoxide and hydrogen ions.
