[ostudent]

Hi all,

I'm having a hard time understanding what's going on in C13 NMR.
For proton NMR, it makes sense that the spectra allows determination of protons in a molecule. The protons are already there.

However, the C13 isotope isn't present in any natural compounds, right?
So, then, how would you detect it in C13 NMR? I read in text that C13 atoms almost never occur together in the same molecule.

Or is there an underlying assumption that you could theoretically synthesize a molecule like butane but with one C13 and the others remain as C12.

sorry for the inconvenience of explaining this. I think there's something fundamentally missing in my understanding this whole NMR thing^^

[Corribus]

However, the C13 isotope isn't present in any natural compounds, right?

No, natural change of 13C is on the order of 1%.

[Enthalpy]

Humans purify ¹³C and put the atoms where desired in the observed molecule - when this is wanted and worth the effort. You can for instance search the web for:
13C "Sigma Aldrich"

"Almost never" is an exaggeration. The natural abundance of ¹³C being 1.08%
https://www.webelements.com/carbon/isotopes.html
18% of glycerol trioleate molecules C₅₇H_xO_y, a natural vegetable oil, contain two ¹³C at random locations.

[Babcock_Hall]

@OP, So if 1.1 % of C-13 nuclei have a second C-13 nuclei next to them, then what does this suggest about observing lines that originate from one-bond carbon-carbon coupling?