Why is 1,3-dinitrophenol more acidic than 1,5 or 1,6?

[whdw]

I know that ortho(1,2) meta(1,3) and para(1,4) nitrophenols make it more acidic.
But if you compare nitrophenols on the (1,3) (1,5) and (1,6) positions on the benzene ring, which is more acidic?

 

[chemisttree]

I assume by the 1,6-, 1,2- nomenclature you are using that these are mononitrophenols. Look again at you rules for nomenclature. Are the 1,6- and 1,2- isomers different from each other?

 

[whdw]

Isn't 1,6 basically the same as 1,2?

 

[JJMB]

p-nitrophenol and o-nitrophenol would be more acidic than m-nitrophenol. p and o-nitrophenol would be approximately the same acidity.

Tip: Try drawing out the resonance structures for each conjugate base to understand.

Best of luck,

-JJMB

Edit: The isomers which have the most stable resonance structures for their conjugate bases will be the most acidic. The nitrogen in the nitro group carries a partial positive charge because of the electron withdrawing oxygens. So resonance structures that have a negative charge adjacent to the nitrogen for example, will be more stable.

 

[whdw]

Thanks to both of you guys for your help!

whdw