para vs. meta nitrophenol

[ssh18]

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Why is para nitrophenol more acidic than meta nitrophenol? I worked out the resonance and even in meta, the electrons do move around? Is it a matter of the electrons being able to move all around the ring in a para setting vs. meta?

I'm a bit confused. Thanks!

 

[armybound]

does it have anything to do with the -OH being ortho/para directing & activating and thus more stable?

and the nitro is meta-deactivating, isn't it?

 

[RSAgator]

are ortho, meta, para ring systems on the exam?

 

[armybound]

are ortho, meta, para ring systems on the exam?

you might be asked which product is predicted to be most abundant

 

[J ROD]

I can not remember exactly but it has to do with an electron withdrawing (NO2) group at the ortho/para position and resonance abilities.

 

[bluemonkey]

Try drawing out the resonance forms for both the meta and para. With the para notice that you can take the a lone pair from the oxygen that has lost a hydrogen, drop them into the carbon they are attached to, move the double bond between carbons 1 and 2 to between carbons 2 and 3, and then take the double bond from between carbons 3 and 4 and move these electrons onto the nitrogen then moving one of the electron pairs between oxygen and nitrogen and move it onto the oxygen. You cannot do this with the meta postion. I hope this helps...

 

[ssh18]

So, in the para nitrophenol, the electron is basically able to move around from the O that has lost a proton all the way to the nitrogen, which is not the case in meta nitrophenol?

Also, here is a general question about resonance:

If there is a pi bond between carbons 1 and 2, that pi bond can move to carbons 2 and 3. What about lone pairs? if there is a lone pair on carbon 1, it can move to carbon 2 and then 3 and so forth? so basically, lone pairs can travel one atom at a time?

 

[Foghorn]

Ummm....lemme think about it. Here's a reference to similar question
http://forums.studentdoctor.net/showpost.php?p=5423585&postcount=623


Edit:

Why is para nitrophenol more acidic than meta nitrophenol? I worked out the resonance and even in meta, the electrons do move around? Is it a matter of the electrons being able to move all around the ring in a para setting vs. meta?

I'm a bit confused. Thanks!

Remember the relative acidity of a molecule is related to the stability of the conjugate base formed when deprotonated. In this case, the para-structure has more resonance contributors relative to the meta structure indicating the the para-structure conjugate base is more stable than meta conjugate base. As you've indicated it's a matter of moving electrons around after deprotonation.

 

[Foghorn]

Oops...double post.

 

[BlackSails]

you might be asked which product is predicted to be most abundant

Maybe choose b/w ortho/para and meta. If you can sort out ortho/para ratios, I have a prize for you to pick up in Stockholm

 

[BloodySurgeon]

I didn't read other ppls response, so I will just assume that the answer was given but I wanted to just ask another note. I remember an experiment that I did a long time ago with dyes and we had to convert it to some sort of quinone and I remember that the para position for a benzoquinone was unusually stabilized due to some reason that pertained to the delocalized electrons moving straight through the beneze (or something like that). I don't know if this is relevant but if you get the double bound on the nitrogen and one on the oxygen for a para-nitrophenol, it could be a similar problem.

 

[lDanny]

In TPR its just says that in the meta position, it can't delocalize the charge... so why can't it delocalize the charge in that position? Thanks

 

[loveoforganic]

In TPR its just says that in the meta position, it can't delocalize the charge... so why can't it delocalize the charge in that position? Thanks

draw the resonance structures. it's saying you can't delocalize the charge onto the two oxygens in the nitro group.

 

[sleepy425]

i expect more replies

sigh, this is a surefire way to not get constructive replies

 

[lDanny]

draw the resonance structures. it's saying you can't delocalize the charge onto the two oxygens in the nitro group.

oh ok, that makes sense. Thanks for the replies! I appreciate all the help from you guys! 👍

ya dude, don't say that you expect stuff from other people... they are helping because they want to, not because they have to..

 

[thebillsfan]

instead of drawing out the resonance structures, can we just know that nitro is meta directing, which means its NOT para directing, and if its meta directing that means it directs the pi electrons towards the meta position and away from the para position? fewer electrons in the para position make para more acidic. even if this is not technically accurate is that a valid way to think about it?

 

[loveoforganic]

That is so convoluted compared to just knowing where electrons go! I can't even decipher all of it 🙁

 

[thebillsfan]

That is so convoluted compared to just knowing where electrons go! I can't even decipher all of it 🙁

haha, well, i think drawing in the resonance structures can be ambiguous (does it go ON the carbon or in between?). all i was trying to say was that, since nitro groups are meta directing, the reason they're meta "directing" is because they redirect the electron density to the meta position. that means the electron density is moved away from the para group (the alcohol) in para-nitrophenol, making the hydrgoen more acidic. if it was meta-nitrophenol, the electron density would be directed to the meta group (the alcohol) which would make the hydrogen more acidic. did that make a little more sense, and is that still correct?

 

[loveoforganic]

They're not electron directing. They're an electron withdrawing subsituent. They just withdraw the LEAST electron density from the meta positions. They withdraw the MOST electron density from the o/p positions.

 

[thebillsfan]

oh right, well that works for me also. thank you!