Advantages of ¹³C NMR:

¹³C nmr provides a signal for each non equivalent carbon atom in a molecule and this gives   direct details about the carbon skeleton. In contrast, ¹H nmr provides details about the carbon skeleton indirectly and provides no information about quaternary carbon atoms like carbonyl carbons. Another advantage of ¹³C NMR is the broad range of chemical shifts. The signals are spread over 200 ppm as compared to 10 ppm for protons. This means that signals are less probable to overlap. Furthermore, each signal is a singlet. This can as well be a disadvantage as information about neighboring groups is lost. Though, there are techniques that can be employed to address this problem. For instance, information about the number of protons attached to each carbon atom can be acquired by off resonance decoupling. In this method, the ¹³C spectrum is run such that all the protons are decoupled apart from those directly attached to the carbon nuclei. Therefore, the methyl carbons (CH₃) appear as a quartet, the methylene carbons (CH₂) appear as a triplet, the methine carbons (CH) appear as a doublet and the quaternary carbons (C) still emerge as a singlet.

Practically, off resonance decoupling is rarely employed nowadays because a technique termed as DEPT is more convenient and easier to analyze. Unfortunately, it is not feasible to cover the theory behind this method here. Though, knowledge of the theory is not essential in order to interpret DEPT spectra. Such type of spectra can be run so that only one type of carbon is detected. Other words, a DEPT spectrum can be run so that just only the methyl signals are detected or the methylene signals, etc. This permits us to distinguish all four types of carbon, but it means which we have to run four different spectra. There is a quicker way of getting similar information via only running two spectra. A DEPT spectrum can be run such that it picks up the methyl and methine carbons as positive (+ive) signals and the methylene carbons as negative (-ive) signals (that is the signals go down from the baseline instead of up). The quaternary carbons are not observed. Hence this one spectrum permits you to identify the quaternary signals by their nonexistence and the methylene signals that are negative. We still have to differentiate between the methyl signals and the methine signals, but this can be done via running one more DEPT spectrum such that it only picks up the methine carbons.