nitrophenol

[houstongirl]

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m-nitrophenol and o-nitrophenol
why o-nitrophenol is more acidic.?


also, n(ch3)2 is strongly activating P/O
nitro is deactivating meta directing
when both are on a benzen ring and placed meta to each other when adding kmno4/h2so4 the dimethyl amino group overposers the nitro group. can someone please explain why this takes place.

thanks

 

[allstardentist]

o-nitrophenol is more acidic cuz the conjugate base is resonance stabilized while m-nitrophenol is not.

activating group overpowers deactivating group.

 

[houstongirl]

If you don't mind can you explain why m nitrophenol will not stablized by resonse

 

[denteng]

increase electron withdraw = increase acidity

o-position is closer than m-position. hope it helps.

m-nitrophenol and o-nitrophenol
why o-nitrophenol is more acidic.?


also, n(ch3)2 is strongly activating P/O
nitro is deactivating meta directing
when both are on a benzen ring and placed meta to each other when adding kmno4/h2so4 the dimethyl amino group overposers the nitro group. can someone please explain why this takes place.

thanks

 

[leadmeg]

Take off the proton in the phenol group assuming that it was deprotonated by the base outside.

You will have minus charge on O (O-), and try to move the minus charge around the phenol molecule.

You will find that the minus charge will only sit on ortho and para position.
Thanks to the electron withdrawing (electron hungry) group, nitro group, on the ortho or para position will happily pull the minus charge via resonance.
However meta positioned nitro group even though they are the same electron hungry there is no way they can share that delicious minus charge via resonance.
They (meta nitro) at best can taste the minus charge via inductive effect. And it is generally (at the level of undergrad ochem) true that resonance effect is more significant in stabilization than the inductive effect is.

Therefore ortho or para positioned electron withdrawing group contribute to additional delocalization of the minus charge, which is good for stabilization of the whole molecule. Resonancewise, phenol and m-nitrophenol has the same number of resonace structures.
(oxygen of the phenol group is very electronegative but they don't want to hold the minus charge forever (localized) in their hands).

The one which is more stable with the proton taken off is more acidic than the other one.