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Counting Carbon Environments

Hi guys,

Specifically my question is about in aromatics - how do you count the number of carbon environments for NMR? I don't really get it at all.

For example in Phenol - are there two environments? One for all of the carbons and another for No.1 (bonded to the OH group?)

Cheers.
Alex.
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TiTo20
7
Original post by Alexdaman93
Hi guys,

Specifically my question is about in aromatics - how do you count the number of carbon environments for NMR? I don't really get it at all.

For example in Phenol - are there two environments? One for all of the carbons and another for No.1 (bonded to the OH group?)

Cheers.
Alex.


With carbon NMR, you should look for ONE line of symmetry, that will help you decide how many carbon environments there are.

So looking at phenol, where is the line of symmetry?

Next, you should remember from your studies that different groups attached on the ring affect subsequent carbons around the ring.

So for example, if it was nitrobenzene, then there will be a peak for the carbon attached directly onto the nitro group, (Carbon no.1) then one peak for carbon no.2, one peak for carbon no.3, and then one peak for carbon no.4. However, since there is symmetry in nitrobenzene, carbon 5 is in the same environment as carbon 3, and carbon 6 is in the same environment as carbon 2. Therefore, in nitrobenzene, there are 4 peaks =]

So with phenol, which carbons will produce a peak and which carbons are the same? How many will there be?


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Reply 2
Avatar for Alexdaman93
Alexdaman93
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2
So, in Phenol, Carbons 1, 2+3, 4+5, 6 produce peaks?

What about then in, say, 2methylphenol?

Carbon 1 makes a peak, carbon 2 does, carbon 3 does, carbons 4+5 do, carbon 6 does?

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