organic chemistry - Differences between phenols and alcohols

I know phenols are more acidic as compared to alcohols, but are they considered different from alcohols?

Sure, you can study something as a subset, but are phenols considered a subset of alcohols, or are they considered as completely different from alcohols? My confusion is due to the fact that both of them contain a hydroxyl group.

Answer

Nope. Alcohols consist of an -$\ce{OH}$ group bonded to a saturated carbon ($\mathrm{sp^3}$ hybridized, no multiple bonds).

IUPAC says:

Compounds in which a hydroxy group, -$\ce{OH}$, is attached to a saturated carbon atom $\ce{R3COH}$. The term 'hydroxyl' refers to the radical species, $\ce{HO^.}$.

and

Compounds having one or more hydroxy groups attached to a benzene or other arene ring, e.g., 2-naphthol:

_{(source: iupac.org)}

A phenol consists of an -$\ce{OH}$ bonded to an unsaturated $\mathrm{sp^2}$ carbon. Thus, it does not qualify as an alcohol. One can classify it as an enol, though.

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Really, to me, the classification doesn't matter. Classifications are artificial, what is important is, how well the properties fit in the classification.

Many of the alcohol properties depend upon:

• Its unsaturated nature: oxidation to ketone/aldehyde/acid


• The weaker $\ce{R-O}$ bond and its ability to easily break and form an $\ce{R+}$ cation (this makes it a good participant in $\mathrm{S_N1}$ reactions)

Phenol can obviously not be oxidised at the $\ce{OH}$ to a ketone/acid (though one can do stuff to make it into a quinone). Phenylic carbocations are unstable, thus we don't get any $\mathrm{S_N1}$ reactions, and the $\ce{Ph-O}$ bond stays put.

On the other hand, most of the reactions of phenol depend upon its

• Aromatic phenyl ring: All the EAS reactions


• Weaker $\ce{O-H}$ bond (i.e., acidic nature): Reimer-Tiemann reaction, etc.

Thus phenols and alcohols don't have too many reactions in common. So, in this case, they have been classified in a sensible manner--if phenols were classified as alcohols, we would basically be clubbing two radically different classes of compounds under one umbrella.