Carbon-13 NMR - DEPT Spectra

DEPT Spectra

DEPT stands for Distortionless Enhancement by Polarization Transfer. It is a very useful method for determining the presence of primary, secondary and tertiary carbon atoms. The DEPT experiment differentiates between CH, CH₂ and CH₃ groups by variation of the selection angle parameter (the tip angle of the final 1H pulse):

• 135° angle gives all CH and CH₃ in a phase opposite to CH₂
• 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 1H to 13C has the secondary advantage of increasing the sensitivity over the normal 13C spectrum (which has a modest enhancement from the NOE (Nuclear Overhauser Effect) due to the 1H decoupling).