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Topic: Determining Unknown Compound (IR/H NMR)  (Read 8001 times)

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Offline bmilla35

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Determining Unknown Compound (IR/H NMR)
« on: March 22, 2012, 05:57:02 PM »
I'm reallllyyyy struggling with this. The IR isn't all that clear, but the stretch from 3500-2500 leads me to believe that a Carboxylic Acid is present. If that's the case, where is the stretch for the carbonyl group? The 3 singlets on the H NMR throw me off even more!

I know it shouldn't be that hard, but I just can't get it. Any sort of guidance would be appreciated.

Added info:
-C NMR shows 6 peaks
-Formula is C8 H10 O2



Offline orgopete

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Re: Determining Unknown Compound (IR/H NMR)
« Reply #1 on: March 22, 2012, 10:39:15 PM »
Let’s start with the NMR. There is an aromatic ring, and peaks with 2, 3, and 1 hydrogen. The peaks with 2, 3, and 1 hydrogen do not have any adjacent hydrogens (sort of). If you have an aromatic ring, that only leaves two carbons to place. Surely you can come up with at least one possible structure.
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Offline bmilla35

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Re: Determining Unknown Compound (IR/H NMR)
« Reply #2 on: March 22, 2012, 11:07:53 PM »
Let’s start with the NMR. There is an aromatic ring, and peaks with 2, 3, and 1 hydrogen. The peaks with 2, 3, and 1 hydrogen do not have any adjacent hydrogens (sort of). If you have an aromatic ring, that only leaves two carbons to place. Surely you can come up with at least one possible structure.

Thank you for the reply. So that the signal at 1600 ISSSS an aromatic? Where is the carbonyl signal at 1700 from the carboxylic acid?

Offline bmilla35

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Re: Determining Unknown Compound (IR/H NMR)
« Reply #3 on: March 22, 2012, 11:15:11 PM »
I suppose it there could be two ether functional groups, but the only reason I didn't think of that is we didn't go over it in class.

Offline orgopete

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Re: Determining Unknown Compound (IR/H NMR)
« Reply #4 on: March 23, 2012, 12:14:13 AM »
I'm not sure what you are thinking. C8H10O2 - C6H4 = C2H6O2

Let me assume you believe there is a COOH group.

C2H6O2 - CO2H = CH5

Hydrogens come in 1s, 2s, and 3s. There are two carbons and you need three peaks. Don't even look at your NMR or IR. Can you think of any structural features that would have 2Hs, 3Hs, and 1H? Add two oxygen atoms and draw all possible structures. No let's limit it. The aromatic region is symmetrical. It has para substitution. Now draw everything you can think of. That is your compound.
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Offline bmilla35

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Re: Determining Unknown Compound (IR/H NMR)
« Reply #5 on: March 23, 2012, 01:46:08 AM »
Once again, thank you for your help and continued patience.

I can come up with a structure that fulfills those requirements but not without an ether. Like i previously mentioned i'm hesitant to include even consider because we have never gone over it..

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