Why is Phenol more acidic than other alcohols?

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onedirection

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So Phenol is more acidic because of the resonance that exists with the benzene ring this is what doesn't make sense.

if it has resonance that means that it has more stability, then it is less likely to dissociate, therefore it doesn't like to dissociate, so wouldn't that mean it is less acidic because strong acids dissociate readily?
 
So Phenol is more acidic because of the resonance that exists with the benzene ring this is what doesn't make sense.

if it has resonance that means that it has more stability, then it is less likely to dissociate, therefore it doesn't like to dissociate, so wouldn't that mean it is less acidic because strong acids dissociate readily?

When they are referencing to stability, they are considering the conjugate base of phenol (the phenoxide anion). Looking at the conjugate base of phenol, we see that the negative charge can be delocalized by resonance to three different carbons on the aromatic ring.

phenol_02.gif


Although these are all minor resonance contributors (negative charge is placed on a carbon rather than an oxygen), they nonetheless have a significant effect on the acidity of the phenolic proton. Essentially, the benzene ring is acting as an electron-withdrawing group.

The fact that this phenoxide anion is more stabilized, the product of this dissociation, would indicate that phenol is more acidic than your standard alcohol.

You'll probably find more help in the MCAT Question & Answer forum, here: http://forums.studentdoctor.net/forumdisplay.php?f=134,
or if you'd like, you can add me on skype: doctadna. I'll be having a review session and will discuss the topic of acidity and how resonance and other factors play an important role.
 
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To summarize DNA's explanation in the context of your question, the conjugate base of phenol (phenoxide) is the form stabilized by resonance, so existence in this form, post-dissociation of phenol, is favored. Phenol itself doesn't experience resonance with the lone pairs on the oxygen atom.

Also, moving to Q&A.
 
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