Destroyer OCHEM #5

[Demps]

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For p-nitroaniline and o-nitroaniline,

what methods are used for the separation of these two isomers?

a) column chromatography
b) crystallization
c) IR spectroscopy
d) A and B
e) all of these

Answer is D.

but how would these two be separated from column chromatography? they virtually have identical substituents attached to the ring and the same molecular mass...

 

[needzmoar]

For p-nitroaniline and o-nitroaniline,

what methods are used for the separation of these two isomers?

a) column chromatography
b) crystallization
c) IR spectroscopy
d) A and B
e) all of these

Answer is D.

but how would these two be separated from column chromatography? they virtually have identical substituents attached to the ring and the same molecular mass...

They are constitutional isomers so they'll exhibit different physical properties.

 

[LuckyTangerines]

The substituents in o-nitroaniline are close enough to hydrogen bond intramolecularly with each other and so the molecule as a whole won't interact with the polar adsorbent as much in column chromatography. On the other hand, p-nitroaniline has its substituents far away that the NO2 group in the molecule would interact with the adsorbent and stay in the column longer. So in the end, o-nitroaniline will elute from the column first followed by p-nitroaniline. Hope this helps!

 

[Vsno123]

The substituents in o-nitroaniline are close enough to hydrogen bond intramolecularly with each other and so the molecule as a whole won't interact with the polar adsorbent as much in column chromatography. On the other hand, p-nitroaniline has its substituents far away that the NO2 group in the molecule would interact with the adsorbent and stay in the column longer. So in the end, o-nitroaniline will elute from the column first followed by p-nitroaniline. Hope this helps!

Don't the para isomers crystallize out in the first place so it's not even in the mother liquor? The para isomers crystallize out because of their nice symmetry. And then the mother liquor is then run through the column to isolate the ortho isomer from the solvent and any other compounds that may be mixed in. At least that's my understanding...anyone feel free to correct me if I'm wrong. I hate lab questions.

 

[Demps]

They are constitutional isomers so they'll exhibit different physical properties.

Thanks. I think this is enough the discussion above is too detail! I hate lab questions too... argh

But thanks guys

 

[Gomsemari]

for anyone who's still confused on this question, the answer is :
The para isomer will crystallize out of solution, the ortho isomer will not. The crystals are isolated and the mother liquor is run through a column to purify the ortho isomer.


I dont know the exact reasoning here, but here;s the answer, and if anyone can reason this out, it'll be great 🙂