Distortionless enhancement by polarization transfer (DEPT) is an NMR method used for determining the presence of primary, secondary and tertiary carbon atoms. The DEPT experiment differentiates between CH, CH and CH groups by variation of the selection angle parameter (the tip angle of the final H pulse): 135° angle gives all CH and CH in a phase opposite to CH; 90° angle gives only CH groups, the others being suppressed; 45° angle gives all carbons with attached protons (regardless of number) in phase.
Signals from quaternary carbons and other carbons with no attached protons are always absent (due to the lack of attached protons).
The polarization transfer from H to C has the
secondary advantage of increasing the sensitivity over the normal C
spectrum (which has a modest enhancement from the nuclear overhauser effect (NOE) due to the H decoupling).