PKa of 2-nitrophenol vs 3-nitrophenol

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In summary, the question is which has a higher pKa, 2-nitrophenol or 3-nitrophenol, and why. The pKa values were found to be 7.17 and 8.28, respectively. The difference in electronegativity of the -NO2 group may play a role in stabilizing the conjugate base of 3-nitrophenol, but further discussion is needed.
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flybynight
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Homework Statement


I am given the structures for 2-nitrophenol and 3-nitrophenol, and asked which one has the higher pKa and why.

Homework Equations


pKa=-log(Ka)

The Attempt at a Solution


I looked up the pKas in a reference and found the pKa of 2-nitrophenol to be 7.17 while the pKa of 3-nitrophenol to be 8.28. My question is why, though. The structures are very similar. I was wondering if the electronegative -NO2 (being father away from the O- than in 2-nitrophenol) would stabilize the conjugate base of 3-nitrophenol, by delocalizing the negative charge, making it more willing to give up the proton. However, the opposite seems to be the case.

Any hints?
Peter
 
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  • #3
Thanks Borek. I didn't see that one.
 

What is the significance of the PKa values of 2-nitrophenol and 3-nitrophenol?

The PKa values of 2-nitrophenol and 3-nitrophenol indicate the strength of their respective acidic properties. A lower PKa value indicates a stronger acid, while a higher PKa value indicates a weaker acid.

How do the PKa values of 2-nitrophenol and 3-nitrophenol compare?

The PKa value of 2-nitrophenol is 7.15, while the PKa value of 3-nitrophenol is 8.39. This suggests that 2-nitrophenol is a stronger acid than 3-nitrophenol.

What factors influence the PKa values of 2-nitrophenol and 3-nitrophenol?

The PKa values of 2-nitrophenol and 3-nitrophenol are influenced by the electron-withdrawing effects of the nitro group and the position of the nitro group on the phenol ring. The closer the nitro group is to the hydroxyl group, the stronger the acid will be.

How do the PKa values of 2-nitrophenol and 3-nitrophenol affect their reactivity?

The differences in the PKa values of 2-nitrophenol and 3-nitrophenol can impact their reactivity in chemical reactions. 2-nitrophenol, being the stronger acid, will be more readily deprotonated and therefore more reactive than 3-nitrophenol.

How can the PKa values of 2-nitrophenol and 3-nitrophenol be experimentally determined?

The PKa values of 2-nitrophenol and 3-nitrophenol can be experimentally determined using various methods such as acid-base titration or spectrophotometry. These techniques involve measuring the concentration of the acidic and conjugate base forms of the compounds at different pH levels.

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