joonkimdds

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7+ Year Member
Jun 30, 2005
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Hi, I was doing NMR questions and got stuck when I came across aromatic structures.

When we count NMR, I believe that we only count 1 from each when a structure is perfectly symmetrical.
Does that mean ortho, meta, and para are all the same and thus have only 1?
I drew some pictures here, hoping to learn more about NMR for aromatic rings.

If you got time to do at least 1 of them, could you tell me how many H-NMR and C-NMR you expect from the following pictures?

Thanks.

 

Kneecoal

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Mar 2, 2009
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talking CNMR, for the first one i would expect to see 3 signals - 1 for the methyl, 1 for the C connecting the methyl to the rest of the ring, and 1 for the 2 C's on either side, because they're equal -- because the other half of the ring is the same, those signals are "canceled out" (edit: but don't take my word for it...?)

2 for the second one (next to the first one), 5 for the 3rd one, 2 for the 4th one, 4 for the 5th one, 5 for the 6th one.

editing: for H NMR i found a site that says 1,4 dimethylbenzene (the first one) will have 2 singlets. one around 2 for the methyl H's and one around 7 for the disubstituted benzene ring. i'm afraid i won't be much help for the other questions... and here's that site... they're little true/false quizzes it looks like.

http://www.mp-docker.demon.co.uk/as_a2/topics/nmr_without_ss/index.html
 
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