Coupling between ¹³C nuclei:

Not like the ¹H nmr where spin spin coupling is observed between different protons, coupling among the different carbon nuclei is not observed in ¹³C NMR. This is because of the low natural abundance of ¹³C nuclei. There is just only 1.1% chance of any particular carbon in a molecule being present as the ¹³C isotope. For several medium sized molecules encountered through organic chemists, this effectively means that there will just only be one ¹³C isotope present in a molecule. The chances of comprising two ¹³C isotopes in the same molecule are very small, and the chances of two ¹³C isotopes being on neighboring carbons are even smaller, so much that is why they are negligible.