New Help Finding the Structure from NMR/IR Spectras

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locrian37
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Hi,

My tutorial have been set this http://www.stolaf.edu/depts/chemistr...d/index.htm?15 NMR/IR interpretation question and we've no idea what to do, we know what the structure is but no idea how to justify the position of the carboxylic acid. Can someone help us out?
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locrian37
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please?
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EierVonSatan
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What makes you think you have a COOH group? I don't think you have one. The H-NMR tells you about the substituiton pattern on the ring(s) - for example you can see that one of the rings is symmetrical since you have 2 roofing peaks with integration 2.
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locrian37
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(Original post by EierVonSatan)
What makes you think you have a COOH group? I don't think you have one. The H-NMR tells you about the substituiton pattern on the ring(s) - for example you can see that one of the rings is symmetrical since you have 2 roofing peaks with integration 2.
Hmm...We cheated and looked at answers published by another source and we also got extra help from a lab demonstrator who gave us a molecule that wouldn't have a COOH group.

We then used some software to generate the predicted NMRs of both molecules but they were too inaccurate to tell us which was which for sure.

This was the structure that our lab demonstrator gave us: http://i.imgur.com/f0e60JE.jpg

However, either way, i'm not sure how to justify the position of the -OH group from the NMRs... The IRs don't tell me much either...
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EierVonSatan
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(Original post by locrian37)
This was the structure that our lab demonstrator gave us: http://i.imgur.com/f0e60JE.jpg
Yeah, that's what I would have said it was :yes:

However, either way, i'm not sure how to justify the position of the -OH group from the NMRs... The IRs don't tell me much either...
IR rarely tells you anything important, NMR and MS are much more important - IR is often an after thought.

Consider a disubstituted benzene ring and how the proton signals change when you have them 1,2 1,3 and 1,4 substituted. Draw something simple on chemdraw and use it's predictor if you're still struggling.
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