PKa of 2-nitrophenol vs 3-nitrophenol

[flybynight]

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

 

[Borek]

Try: https://www.physicsforums.com/showthread.php?t=50570

 

[flybynight]

Thanks Borek. I didn't see that one.