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Homework Help: PKa of 2-nitrophenol vs 3-nitrophenol

  1. Sep 17, 2011 #1
    1. The problem statement, all variables and given/known data
    I am given the structures for 2-nitrophenol and 3-nitrophenol, and asked which one has the higher pKa and why.

    2. Relevant equations

    3. 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?
  2. jcsd
  3. Sep 18, 2011 #2


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    Staff: Mentor

  4. Sep 18, 2011 #3
    Thanks Borek. I didn't see that one.
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