I was given a help on brainmass:
"4-Vinylbenzoic acid is an aromatic carboxyllic acid. there are three distinct groups in this molecule: benzene ring,vinyl group and -COOH group. In all there should be 6 NMR peaks .2 peaks corresponding to Ar-H, 3 peaks due to the vinyl group and one peak due to -COOH group. You are getting exactly what is expected. The peak at 6.8ppm which you are looking as quartet is actually a dd and is due to vinyl group. There are two protons adjacent to the aromatic protons which couple and give two doublets. The -COOH group has a great tendency for association it gives a broad band in NMR as well as IR. An important feature connected with vinyl group is the presence of cis and trans hydrogen which responsible for the issues under discussion."
But I still don't know how I write this in lab report and also what is dd? Does it mean two doublets? At 6.8ppm, which proton is it talking about? "Two protons adjacent to the aromatic protons" - is it talking about the two protons on the very far right? I thought that the highest splitting you can get it triplet, because the proton which I highlighted above (in bold) is within 3 bonds distance to 2 protons not 3 protons. And so on. As you can see, I am very confused. I could do simple NMR questions, but this one I'm stuck with.
I have to give the interpretation of 4-vinylbenzoic acid in the way shown in the example below:
1H-NMR (250MHz, D2O): δ=3.55 (t,2H,3JH-H=6.3,a), 4.12-4.15 (s and t overlapped, 4H, b,d), 6.53 (s,1H,c).
I would be greatly appreciated if you could do the same for 4-vinylbenzoic acid (like the example) and explain why it is written like that so when I am asked a similar question again, I can do it myself.© BrainMass Inc. brainmass.com March 21, 2019, 12:51 pm ad1c9bdddf
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