Which is more acidic, alcohol or phenol? [duplicate]








**This question already has answers here**:
 
 




[Reason for the stronger acidic property of phenol than alcohol](/questions/9074/reason-for-the-stronger-acidic-property-of-phenol-than-alcohol)

 (4 answers)
 


[Differences between phenols and alcohols](/questions/729/differences-between-phenols-and-alcohols)

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Closed 2 months ago.



My teacher taught yesterday that though resonance happens in phenoxide ion, it is less stable because the negative charge gets distributed over the carbons in the ring. And hence, alcohols are more acidic than phenols.


His argument seemed convincing at the time but then I searched the Internet about it and everywhere it says that phenol is more acidic than alcohol.


So *which is it?*




The teacher misspoke. It's true that negative charge is relatively unstable in most cases when it's distributed over carbon atoms only, like let us say an allyl anion $(\ce{CH2=CH-\overset{-}{C}H2}).$ But if a more electronegative atom, most commonly oxygen, anchors the bulk of the negative charge then the anion is stabilized; and any delocalization onto carbon atoms only adds to this stability. Phenoxide will in effect concentrate as much of the negative charge on oxygen as it needs to be reasonably stable and delocalize the rest; one oxygen atom plus some carbon atoms beats the oxygen atom alone.


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Is it possible that you misunderstood? If not, your teacher is absolutely wrong. The resonance in phenoxide ions stabilizes the negative charge compared to alkoxide ions.


Phenol has a pKa of 9.95 in water, while methanol has a pKa of 15.5.[1]
Whatever explanation we might use to explain it, the simple fact is that phenols are more acidic than alcohols.


[1] <https://organicchemistrydata.org/hansreich/resources/pka/pka_data/evans_pKa_table.pdf>


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