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I have a molecule and an NMR spectrum, and I need to assign the NMR peaks to each of the carbons to the molecule:

13C NMR, CDCl3, 100 MHz, ethyl 2-oxo-3,4-dihydrochromene-3-carboxylate

I know that the 14.19 ppm and the 61.94 ppm correspond respectively to the carbon 12 and 11. However, I struggle for the other peaks especially between 116.76 and 148.51 ppm. I just know that it corresponds to the aromatic ring. Finally, I think that the 156.65 ppm and 155.15 ppm are respectively the carbon 9 and 10.

I also have the 1H NMR for this molecule:

enter image description here

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  • $\begingroup$ The name of the compound and your numbering are not consistent. $\endgroup$ – Mathew Mahindaratne Feb 2 at 21:54
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    $\begingroup$ It is, for all intents and purposes, impossible, or at least extremely difficult to assign a bare 13C NMR of a moderately complicated molecule with no other information. You should at the very least get a 1H spectrum and HSQC, and perhaps after that a HMBC for your quaternaries. In the absence of that, the best you can do for this compound is to circle a bunch of peaks in the 110–160 ppm region and mark them as "aromatic". $\endgroup$ – orthocresol Feb 2 at 22:15
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    $\begingroup$ In addition to @orthocresol comments, I'd say $\pu{155.2 ppm}$ is definitely not $\ce{C}$-10. $\endgroup$ – Mathew Mahindaratne Feb 2 at 22:43
  • $\begingroup$ No, the 1H alone isn't enough: you need a HSQC too, or else you can't work out which proton belongs to which carbon. Given that you have five quaternaries which won't show up on a HSQC, I'd actually upgrade the HMBC from a "perhaps you need it" to a "you definitely need it", if you want to unambiguously assign every 13C peak. $\endgroup$ – orthocresol Feb 3 at 12:32

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