¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)

When carbon-13 spectra are simplified by broadband proton decoupling, structural information regarding the attached hydrogens is lost.

Distortionless enhancement by polarization transfer, or DEPT, is a double resonance technique that distinguishes carbons by the number of attached protons.

The DEPT experiment utilizes a complex pulse sequence, where the pulse delay and flip angle are varied.

Now, methyl, methine, and methylene carbons yield distinct signals, whereas quaternary carbons produce no signal.

Observe that the broadband-decoupled carbon-13 spectrum for isopentyl acetate represents the chemical shifts of all nonequivalent carbons.

While signals from all protonated carbons appear in the DEPT-45 spectrum, the DEPT-90 spectrum shows peaks only from the methine carbons.

Finally, in the DEPT-135 spectrum, methyl and methine carbons appear as positive peaks,  while methylene carbons appear as negative peaks.

Taken together, the DEPT spectra provide a valuable tool for structure elucidation.