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Author Topic: 13c nmr of p-nitroaniline  (Read 4061 times)

Offline megarushan

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13c nmr of p-nitroaniline
« on: 18/11/2014 16:56:16 »



why is that chemical shift of no 1 carbon (NH2 group) is greater than no 2 carbon (NO2 group)...and no 3 carbon greater than  no 4 carbon....what are the reasons....
thank you....


 

Offline chiralSPO

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Re: 13c nmr of p-nitroaniline
« Reply #1 on: 18/11/2014 19:31:23 »
The shift of the 13CNMR signals is going to depend largely on the electron density around the given nucleus. In this case we have an amino group (-NH2) which donates electron density to the aromatic pi system, and withdraws electron density from the carbon it is directly bound to (because nitrogen is more electronegative than carbon), and a nitro group (NO2) which withdraws electron density from the aromatic pi system and from the carbon it is bound to. The electronic effects of each substituent on the pi system are most apparent for the nuclei that are ortho and para to that substituent.

Therefore:
-nucleus 1 is shifted downfield due to sigma withdrawing effects of the amino group and because of the pi withdrawing effects of the nitro group.
-nucleus 2 is shifted downfield due to sigma withdrawing effects of the nitrogroup and shifted upfield due to pi donating effects of the amino group.
-nucleus 3 is shifted downfield due to the nitro group pi effects
-nucleus 4 is shifted upfield due to amino group pi effects

the sigma effect dramatically overpowers the pi effects
 

Offline megarushan

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Re: 13c nmr of p-nitroaniline
« Reply #2 on: 19/11/2014 16:15:20 »
thanks.....
 

The Naked Scientists Forum

Re: 13c nmr of p-nitroaniline
« Reply #2 on: 19/11/2014 16:15:20 »

 

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