The Student Room Group

Carbon Aromatic NMR

Seem to be really struggling with carbon nmr, can do straight line compounds very easily but when it comes to aromatic compounds can never seem to get it. So for example the molecule below what steps would I need to go through to get the correct number of carbon environments, is there a definitive method or not, I always seem to be getting 6?? Thanks in advance! :smile:

ImageUploadedByStudent Room1430685704.309556.jpg


Posted from TSR Mobile
There are four.
Reply 3
Reply 4
Original post by Jimmy20002012
Seem to be really struggling with carbon nmr, can do straight line compounds very easily but when it comes to aromatic compounds can never seem to get it. So for example the molecule below what steps would I need to go through to get the correct number of carbon environments, is there a definitive method or not, I always seem to be getting 6?? Thanks in advance! :smile:


In general, you should be looking for symmetries that let you exchange different carbons. In the given example you can draw a line of symmetry across the ring, passing between the two substituted carbons, which should help you see which carbons are equivalent.
Original post by BJack
In general, you should be looking for symmetries that let you exchange different carbons. In the given example you can draw a line of symmetry across the ring, passing between the two substituted carbons, which should help you see which carbons are equivalent.


Is there always a line of symmetry?


Posted from TSR Mobile
Great question I've been wondering this aswell!
So how would you go about this molecule, it does not really have a line of symmetry?

ImageUploadedByStudent Room1430693411.489112.jpg


Posted from TSR Mobile
Yes it does, straight down the middle. There are 4 carbon environments in that one.
Original post by Jimmy20002012
Is there always a line of symmetry?


Posted from TSR Mobile


No, it depends on the substituents on the ring.

Benzene is perfectly symmetrical and has only one environment.

Methylbenzene has a plane of symmetry passing through the methyl and dividing the ring into two identical halves. It has 5 equivalent carbon environments and four equivalent hydrogen environments.

1,2-dimethylbenzene has a plane of symmetry passing between the two methyl substituents. It now has four carbon environments and three hydrogen environments

2-chloromethylbenzene does not have a plane of symmetry and has 7 different carbon environments and 5 different hydrogen environments.
Thanks for all the help guys :biggrin: I get it now!!


Posted from TSR Mobile

Quick Reply

Latest