I'm having trouble reading proton NMR

In summary, the conversation discusses a university lab report assignment on proton NMR for cinnamic acid. The person is struggling to understand the peaks and coupling in the NMR spectrum and is seeking help. They mention that the compound has 8 protons and discuss the expected peaks for each type of proton. However, the NMR spectrum does not match their expectations and they are unsure of what they are doing wrong. They also mention the need for a picture of the NMR spectrum for better understanding.
  • #1
8
0

Homework Statement


OK. So I've been given a uni lab report to write up but we were only told yesterday how to read proton NMR, and it's due in on Monday. I'm not terrible at deciphering it, but the compound I've been given the NMR for doesn't make sense (to me). I have to look at the proton NMR for Cinnamic acid, (http://en.wikipedia.org/wiki/Cinnamic_acid) and talk about the coupling, splitting and so on.

Homework Equations


I know the coupling constant is the change in peak values in ppm x MHz of the machine used.


The Attempt at a Solution


Cinnamic acid has 8 protons, 5 are on the aromatic ring, 2 along the alkene and one on the COOH.
-The COOH proton has 0 adjacent protons and 0 equivalent protons so should have one single peak.
-The alkene proton on the acid end has 1 adjacent proton and 0 equivalent protons. It should have a doublet.
-The aromatic end alkene proton has 1 adjacent proton and 0 equivalent protons as well so it should also show up as a doublet
-The 2 ortho protons on the aromatic are equivalent and have 1 adjacent proton so they should show up as a doublet
-the 2 meta protons are equivalent and have 2 adjacent protons so should show up as a triplet
-The para proton has 2 adjacent protons so should show up as a triplet.


All this said, the NMR doesn't look anything like this. There are 2 triplets at around the 7. mark, which makes sense, but there are some other peaks and I'm not sure whether they're doublets or singles. If they are singles, then the total number of peaks is 6, which works because there are 6 different types of protons. However, for 4 singlet peaks you need 4 protons with no adjacent protons, and this doesn't happen. If the peaks are 2 doublets, then there needs to be 2 protons with 1 adjacent proton, and this doesn't happen either because the COOH proton definitely has no adjacents.

This is really confusing! Anyone know what I'm doing wrong?


-Cheers, Pyridine ;)
 
Physics news on Phys.org
  • #2
Giving us a picture of the Hydrogen NMR would be useful. I've got my org. chem book open to NMR, and I could really use a picture.
 
  • #3
hey Char Limit, I can't find one on the internet anywhere and I don't have a scanner :(
 
  • #4
Could you at least describe the locations of the remaining peaks?
 
  • #5



Hello Pyridine,

It sounds like you are on the right track with your analysis of the proton NMR for cinnamic acid. However, it's important to remember that the chemical shifts and peak patterns can vary depending on the specific instrument and conditions used for the NMR experiment. It's possible that the peaks you are seeing are due to impurities or other factors that are affecting the spectrum.

I would recommend double checking your analysis and also consulting with your lab instructor or a more experienced colleague for guidance. It may also be helpful to compare your results with published NMR spectra of cinnamic acid to see if there are any discrepancies.

In general, NMR can be a challenging technique to interpret, so don't get discouraged! Keep practicing and seeking help when needed, and you will become more confident in reading proton NMR spectra. Good luck!
 

1. What is proton NMR and why is it important in scientific research?

Proton nuclear magnetic resonance (NMR) is a technique used to study the structure and composition of molecules. It is important in scientific research because it provides valuable information about the chemical and physical properties of a substance, which can aid in the identification and characterization of compounds.

2. Why do I have trouble interpreting my proton NMR spectra?

Interpreting proton NMR spectra can be challenging because it requires a strong understanding of chemical shifts, integration, and coupling patterns. Additionally, factors such as sample purity, instrument settings, and solvent choice can also affect the spectra and make interpretation difficult.

3. How can I improve my skills in reading proton NMR spectra?

The best way to improve your skills in reading proton NMR spectra is through practice and familiarizing yourself with the basic principles of NMR spectroscopy. You can also seek guidance from experienced researchers or attend workshops and courses on NMR interpretation.

4. What are some common mistakes to avoid when reading proton NMR spectra?

Some common mistakes to avoid when reading proton NMR spectra include misidentifying peaks, not considering the chemical shifts of solvent and impurities, and overlooking coupling patterns. It is important to carefully analyze the spectra and take into account all relevant factors to avoid misinterpretation.

5. Are there any online resources available for learning about reading proton NMR spectra?

Yes, there are many online resources available for learning about reading proton NMR spectra. These include tutorials, videos, and interactive tools that can help you understand the basics of NMR spectroscopy and practice interpreting spectra. Some popular resources include websites from universities and scientific organizations, as well as online databases and software programs.

Similar threads

  • Biology and Chemistry Homework Help
Replies
5
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
1
Views
736
  • Biology and Chemistry Homework Help
Replies
1
Views
5K
  • Biology and Chemistry Homework Help
Replies
1
Views
2K
  • Special and General Relativity
Replies
30
Views
1K
  • Chemistry
Replies
1
Views
2K
  • Biology and Chemistry Homework Help
Replies
1
Views
3K
  • Cosmology
Replies
1
Views
737
Replies
1
Views
2K
  • Biology and Chemistry Homework Help
Replies
4
Views
3K
Back
Top