Acidity of Nitrophenols: Comparing 1,3, 1,5, and 1,6 Positions on Benzene Ring

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Discussion Overview

The discussion centers on the acidity of nitrophenols, specifically comparing the 1,3, 1,5, and 1,6 positions on the benzene ring. Participants explore the factors influencing acidity, including resonance structures and the effects of substituent positions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that ortho, meta, and para nitrophenols increase acidity, questioning how the 1,3, 1,5, and 1,6 positions compare.
  • One participant challenges the nomenclature used for the isomers, asking if the 1,6- and 1,2- isomers are distinct.
  • Another participant suggests that 1,6 is essentially the same as 1,2, implying a potential equivalence in acidity.
  • It is proposed that p-nitrophenol and o-nitrophenol are more acidic than m-nitrophenol, with p and o-nitrophenol having similar acidity levels.
  • A suggestion is made to draw resonance structures for the conjugate bases to better understand acidity, emphasizing that the most stable resonance structures correlate with higher acidity.
  • Discussion includes the role of the nitro group's electron-withdrawing effect on the stability of resonance structures and, consequently, acidity.

Areas of Agreement / Disagreement

Participants express differing views on the acidity of the various nitrophenol isomers, with no consensus reached regarding the comparison of the 1,3, 1,5, and 1,6 positions.

Contextual Notes

Unresolved aspects include the implications of nomenclature on acidity comparisons and the specific resonance structures contributing to acidity levels.

whdw
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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?
 
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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?
 
Isn't 1,6 basically the same as 1,2?
 
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.
 
Last edited:
Thanks to both of you guys for your help!

whdw
 

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