How to read 1H-NMR- and IR-spectre (for ibuprofen) [closed]








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I have read the answers to related/similar questions. They didn't help.


I have to read a proton-NMR-spectrum and an IR-spectrum of ibuprofen. The structure formula is given to:
[![enter image description here](https://i.stack.imgur.com/SNh3S.png)](https://i.stack.imgur.com/SNh3S.png)


I have not been formally taught how to do this, nor have I solved any problems beforehand. This is because it's **required** for my project, but we haven't had the training like the former classes have for reasons I won't waste time explaining.


I know the very basics of the two spectroscopy methods as I am a high school student.
My questions at the moment have become the following:


1. (proton-NMR) How does di-substituted aromatic rings affect the splitting of the signals from A and B?
2. (IR) Should I only focus on confirming the aromatic ring and carboxylic acid? And do I only have to figure out the fingerprint area or do I have to analyze the whole IR-spectrum?


[Before you take a look at the spectra, I recommend looking at **the last two pages** of this link](https://edu.rsc.org/download?ac=13856)


The spectras are as follows:


***proton-NMR-spectrum: **([Source](https://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_frame_disp.cgi?spectrum_type=hnmr&sdbsno=10570))*****


[![enter image description here](https://i.stack.imgur.com/IuMx2.png)](https://i.stack.imgur.com/IuMx2.png)
[![enter image description here](https://i.stack.imgur.com/WDkkP.png)](https://i.stack.imgur.com/WDkkP.png)


**IR-spectrum: ([Source](https://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_frame_disp.cgi?spectrum_type=ir&sdbsno=10570))**


[![enter image description here](https://i.stack.imgur.com/j7Hdu.png)](https://i.stack.imgur.com/j7Hdu.png)




1. To a *very crude* first approximation, A and B appear as doublets in the NMR. That's because A couples to B and vice versa, and to a first approximation, the AB pair on one side doesn't interact with the AB pair on the other side.  

This is not entirely true, of course. The system is not really two separate AB pairs, but is properly described as AA'BB' (or AA'XX', depending on the exact frequencies involved). This website: <https://organicchemistrydata.org/hansreich/resources/nmr/?page=05-hmr-15-aabb/> and this question: [How can multiplets in para-disubstituted benzene rings be described?](https://chemistry.stackexchange.com/questions/84390) discuss it in more detail, but at your current level, you almost certainly don't need to worry about that.
2. For the IR, I'd focus on picking out whatever you can pick out; what you mentioned is probably enough. It's rare to use the messy region of the IR for structural elucidation. IR still has its uses, but there's a reason why NMR is nowadays considered the 'primary' characterisation technique for typical organic molecules.


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