Multiplet Detection in Coupled or Decoupled 13C

DEPT : Distortionless Enhancement by Polarization Transfer

The DEPT experiment is in fact an improved version of the INEPT experiment. It results also in an enhancement of the intensity of the X-nuclei by a factor of . One of the nicest improvement of this sequence as compared with the INEPT, is that the DEPT experiment does not have to deal with a variable refocusing delay. Indeed, the magnetization from the X-nuclei multiplet is enhanced but "in phase" at the end of the pulse sequence. The intensity of the X nuclei is dependent on the length of the last proton pulse. Therefore, the DEPT experiment is less sensitive to a misset delay (but is very sensitive to proton pulse calibration). As the multiplet behavior of the X-nuclei is created by the last proton pulse, coupled Carbon-13 spectra can be obtained with DEPT enhancement.

The starting point of the DEPT pulse sequence is, as we can see, a 90` pulse on proton. This means the the recycle delay is controlled (like in INEPT) by the proton relaxation rate. The tau delay (1/2J) is chosen to maximize the antiphase components of the proton doublet but unlike INEPT, multiple quantum magnetization is created by the 90` pulse on the X heteronuclei. The second delay serves as a refocusing period for proton chemical shifts.

The proton pulse transform the multiple quantum coherence into observable single quantum coherence. The 180` pulse applied to the X-nuclei ensures proper chemical shift on the X-nuclei. at the end of the third delay, the in-phase magnetization can then be detected (with the proton decoupler turned ON or OFF. The intensity of the X-nuclei signal depends on the lenght of the pulse controls and on the number of protons coupled to to the X-nuclei.

To distinguish the various multiplicity patterns in carbon-13 NMR, three DEPT spectra are acquired:

The three spectra can be combined to provide pure CH, CH2 and CH3 sub-spectra. This is called "ADEPT" editing.

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