Acidity on Phenols

[silveryhair]

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I understand that EWG increase the acidity of compounds on phenols and they are enhanced when they are in the Ortho and Para position, not so much on the meta position.

I know this is probably as stupid question, but would the Ortho position produce a stronger acid than the Para position since EWG is closer to the OH? Thanks

 

[rnbaxter]

I understand that EWG increase the acidity of compounds on phenols and they are enhanced when they are in the Ortho and Para position, not so much on the meta position.

I know this is probably as stupid question, but would the Ortho position produce a stronger acid than the Para position since EWG is closer to the OH? Thanks

Ok the larger the number of electronegative substituents, the stronger the acid. The more electronegative the substituent, the stronger the acid

Now electron withdrawing groups are important for acids because their dipole stabilizes the conjugate base. Donating groups make the conjugate base less stable. Therefore, the closer the withdrawing group to the proton being lost the stronger the acid will be.

 

[silveryhair]

Cool! Thanks Rnbaxer!

 

[JustwantDDS]

Why is it that EWG groups make the acid stronger on o/p?

I know thats the case, but why?

Isnt EWG meta director? (even though thats addition...)

 

[orgohacks]

I understand that EWG increase the acidity of compounds on phenols and they are enhanced when they are in the Ortho and Para position, not so much on the meta position.

I know this is probably as stupid question, but would the Ortho position produce a stronger acid than the Para position since EWG is closer to the OH? Thanks

To answer your last question, yes, due to the inductive effect. Here's an example -

pKa of 2-fluorophenol : 15.6 (most acidic)
pKa of 3-fluorophenol: 15.8
pKa of 4-fluorophenol: 18.0 (least acidic)

source - http://www.chem.wisc.edu/areas/reich/pkatable/