Coupling between ¹³C and ¹H nuclei:

Even though ¹³C-¹³C coupling is not seen, it is possible to see coupling among the ¹³C nuclei and ¹H nuclei. This might appear strange as we have already said that ¹H signals are not observed in the ¹³C spectrum. Though, it is perfectly logical to see coupling between ¹³C and ¹H nuclei even if we don't notice the ¹H signals. This is since the ¹H nuclei will still take up two possible orientations in the applied magnetic ?eld, each of which generates their own secondary magnetic ?eld. Practically, such type of coupling makes the interpretation of ¹³C nmr spectra difficult and thus ¹³C spectra are generally run with ¹³C-¹H coupling eliminated. This is completed by continuously resonating all the proton nuclei whereas the ¹³C spectrum is being run such that the signal for every non-equivalent carbon atom appears like a singlet. This results in a extremely simple spectrum which immediately permits you to identify the number of non-equivalent carbon atoms in the molecule from the number of signals present. This process is termed as proton decoupling. One drawback of this technique is that it distorts the intensity of signals and thus integration cannot be employed to determine the number of carbon atoms accountable for each signal. This distortion is specifically marked for signals due to quaternary carbons that are much weaker than signals for other types of carbons.