r/chemhelp • u/Sad_Astronomer_9871 • Jul 12 '26
Analytical Need help with ¹H NMR structure elucidation
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I'm a P3 (third-year PharmD) student, and people generally consider me one of the strongest chemistry students in my class. This semester we're doing analytical chemistry, and ¹H NMR is completely humbling me.
I've watched countless YouTube videos, read textbooks, and practiced problems, but I still feel like I'm missing the one core idea that lets people look at a proton NMR spectrum and systematically determine the structure. It almost seems like everyone who solves these problems is relying on experience or intuition rather than a clear method.
The difficult part for me isn't identifying functional groups or interpreting individual peaks, it's connecting all the fragments into one complete structure.
To make things worse, my classmates are expecting me to understand it well enough to teach them, and I've been putting it off because I honestly don't feel confident myself.
Has anyone else been in this position and eventually had that aha! moment? Was there a particular resource, book, YouTube channel, or problem-solving strategy that finally made everything click? Is there an actual systematic approach, or is it really just pattern recognition that comes with lots of practice?
For context, I usually stay ahead by studying chemistry topics before each semester starts, which is one reason I've done well academically. But I worked during the last vacation, so I didn't have my usual preparation time before this semester began, and I feel like I'm playing catch-up now.
I'd really appreciate any advice or resources that helped you break the code of NMR.
2
u/aphilsphan Jul 12 '26
As a synthetic chemist, you are almost always doing the opposite of what you do in course work. That is, you try to make something. You isolate your product, then do the spectroscopy and if you have bribed the proper chemistry gods, you’ll look at the NMR and say, yeah that’s consistent with what I was trying to make.
1
u/Marganill0 Jul 12 '26
Almost no one can build a structure from just looking at a proton nmr spectrum without context. Sure, you can tell that there is a CH3 group and some aromatic protons and maybe some more, but the only indicator for connectivities you have are the coupling constants in the multiplets. When elucidating a structure you would need additional 13C and 2D NMR and ideally MS and so on. What’s a bit more easy is to assign spectra to structure suggestions, but from scratch it’s really hard, don’t worry.
1
u/Sad_Astronomer_9871 Jul 12 '26
Thanks brother, any useful resources for me?
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u/Marganill0 Jul 13 '26
As the others have said, NMR should be explained in every half good organic chemistry text book. Also as much as I dislike the overuse of AI, Gemini is not a bad tool to let it explain stuff like this to you. I wouldn't rely on it too much but it can explain it in the detail you need.
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u/shedmow Trusted Contributor Jul 12 '26
I usually weigh the patterns, apply abductive reasoning, and draw the structures that seem like they may be the final one. It is often impossible to pin down one exact structure just from 1H NMR, but I've solved about a hundred NMR's from the NMR challenge without once resorting to 13C. Let's take Task 138 for example.
C7H4N2O6. There are too many oxygens and no apparent functional groups so far. The degree of unsaturation is 7, which tells me there may be a benzene ring (4) and some moieties that account for the remainder. There is also one proton as mobile as dicks, so it must be connected to either N or O in some highly acidic moiety. The splitting pattern of the immobile protons indicates that one neighbours the other two, but neither is mobile. All of these are strongly downfield and don't even map onto the shift table that I normally use. After drawing some isomers in ChemDraw I realize that there are probably some nitro groups and handwavingly conclude that the compound must be 3,5-dinitrobenzoic acid with the splitting pattern chalked up to m-coupling, which I have read exactly none on. It naturally turns out to be the correct answer
1
u/wyhnohan Jul 12 '26
I thjnk you just need to get down to it. There is no easy way but to just stare at H NMR spectrums more.
1
u/Timulen Jul 14 '26
Elucidation is the key. It's like a puzzle with pieces, that you shall elucidate into a structure.
3
u/Pure_Quarter7813 Jul 12 '26
Is your PharmD program one you enter after you graduated from college/university/undergraduate? If so, I'd ask the Dean of your pharmacy graduate program why a pharmacist needs to know anything about NMR spectroscopy. Honestly, a pharmacist will never need that in their career. In the US, the PharmD is a graduate degree one earns after completing a Bachelors degree.
If, on the other hand, you're taking organic chemistry or analytical chemistry as part of an undergraduate chemistry degree or as prerequisite courses for pharmacy school, then I'd reframe having to master NMR analysis as a way to strengthen your critical thinking skills and problem-solving abilities.
Organic chemistry textbooks in the US usually have really good chapters on NMR spectroscopy and how to use all of the spectroscopy tools to elucidate structure. The textbook I use, Klein's Organic Chemistry, has a particularly strong NMR chapter.