I have 1H and 13C NMR spectrum data and need help with interpretation. Inability to interpreted is stalling a project and we need expertise. Anybody can point me to the right experts please? Thank you
Have you tried 2D analysis (COSY, HSQC, HMBC)? It should help to better interpret your peaks.
As for your 1H NMR spectra, let's say, you have three multiplets: A, B and C. You can have a pretty good guess about to which moieties these protons belong based on their chemical environment. Alkyl protons appear at low chemical shifts (e.g., 1-3 ppm), protons attached to a double-bonded carbon atom or aromatic protons will have higher chemical shift (e.g., 6-7 ppm), acidic protons (-OH, -NH, etc.) can be even more downfielded (e.g., 9-10 ppm). Note that these protons are typically invisible in the spectra of aqueous solutions.
Once you have a rough estimate on the order, you can calculate the coupling constants (given your spectrum is well-resolved). For instance, your A peak is a doublet, so is C. The distance between the two peaks in Hz gives the coupling constants. If you find the same value for the peaks of C, they are coupled which normally means that protons A and C are next to each other (or they are even located on the same carbon).
If you measure spectra in organic solvent, you can also integrate the multiplets and their ratio is proportional to the ratio of proton numbers. Let's say your peak area of the A doublet is 1, that of B is 2, and for C it's again 1. So the ratio of protons is 1:2:1. If you know your molecule consists of 8 protons in total, then the absolute numbers are 2, 4 and 2.
These analyses of a one-dimensional 1H NMR spectrum should already provide a lot of information. In the next step you can try 2D COSY to see which proton is coupled to which one (if you cannot calculate the coupling constants), and once you assigned all proton peaks, you can measure a HSQC spectrum where you will see which proton is coupled to which carbon, that helps you to assign the carbon atoms.
Hallo,
It might be good to ask your NMR facility manager. Tell him what you know about the molecule or the mixture, and he maybe could tell you which experiments to run. For assignment of small molecules and connection of 13C and 1H chemical shifts, like Bence Kutus said, 2D experiments like COSY, TOCSY, HSQC, HMQC could help. If you have a mixture you could run a DOSY (diffusion ordered spectroscopy) here you could separate different molecules with different diffusion coefficients. For structure elucidation a NOESY helps. Do you have a mass spectrum?
Many greetings
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