DEPT stands for Distortionless Enhancement by Polarization Transfer. It is a specialized technique used in ^13C NMR spectroscopy to distinguish different types of carbon atoms according to the number of hydrogen atoms directly attached to them. Conventional broadband-decoupled ^13C NMR spectra generally show one signal for each chemically non-equivalent carbon atom, but they do not directly indicate whether a carbon is a CH₃, CH₂, CH, or quaternary carbon. DEPT spectroscopy overcomes this limitation by using polarization transfer from ^1H nuclei to ^13C nuclei. Thus, DEPT is particularly useful for determining the carbon–hydrogen framework of an organic molecule and for assigning ^13C NMR signals. The basic principle of DEPT involves the transfer of nuclear magnetization from protons to carbon-13 nuclei. Since ^1H has a much higher gyromagnetic ratio and is naturally more sensitive than ^13C, polarization transfer can considerably enhance the intensity of carbon signals. Radiofrequency pulses are applied to both ^1H and ^13C nuclei in a carefully controlled sequence. The resulting spectrum depends on the pulse angle used in the DEPT experiment. Different pulse angles produce different responses from CH₃, CH₂ and CH groups. A carbon atom without a directly attached hydrogen atom, that is, a quaternary carbon, does not give a DEPT signal because there is no proton from which polarization can be transferred. One of the important features of DEPT is therefore its ability to differentiate protonated carbon atoms. In a normal ^13C{^1H} spectrum, CH₃, CH₂, CH and quaternary carbons can all appear as positive signals. In DEPT spectra, however, the phase and presence or absence of signals depend on the number of attached hydrogens. This makes DEPT a powerful complementary technique to ordinary ^13C NMR. The most commonly used DEPT experiments are DEPT-45, DEPT-90 and DEPT-135. The number associated with each experiment refers approximately to the flip angle of the final proton pulse used in the pulse sequence. Each type has characteristic signal behaviour. In DEPT-45, the final pulse angle is approximately 45°. Signals from all protonated carbons, namely CH, CH₂ and CH₃, are observed. Quaternary carbons are absent because they have no directly bonded proton. In the usual phase convention, CH,