8: Distortionless Enhancement by Polarization Transfer (DEPT) Spectroscopy
- Page ID
- 332808
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- You can tell how many hydrogens are present on a particular carbon in a 13C NMR spectroscopy by measuring the height of the peaks. [ True or False ].
- The 13C isotope has [ low or high ] abundance.
- The abundance of 13C means that the sensitivity of 13C NMR spectroscopy is [ low or high ].
APT and DEPT
Both the APT (Attached Proton Test) and (DEPT) Distortionless Enhancement by Polarization Transfer are both experiments used for determining the number of protons attached to each carbon in a 13C spectrum. Both experiments yield 13C NMR spectra where the number of attached protons (the multiplicity) is encoded in the phase of the 13C NMR signals.
- APT spectra have quaternary carbons, and methylene carbons phased negative and methine and methyl carbons phased positive.
- DEPT-135 spectra show no quaternary carbons and have methylene carbons phased negative and methine and methyl carbons phased positive.
DEPT is an NMR experiment that involves the transfer of polarization from an excited nucleus to another – most commonly 1H → 13C.
- This is helpful because the abundance of 1H is [ greater or lower ] 13C so the transfer of polarization can increase the sensitivity.
DEPT Spectroscopy Analysis*
* All spectra are either from SDBS (Japan National Institute of Advanced Industrial Science and Technology) or simulated.
The DEPT experiment differentiates between CH, CH2 and CH3 groups by variation of the selection angle parameter:
- 45° angle gives all carbons with attached protons
- 90° angle gives only CH groups, the others being suppressed
- 135° angle gives CH and CH3 peaks pointing up with CH2 peaks pointing down
- Signals from quaternary carbons and other carbons with no attached protons are always absent.
For example, consider the spectrum of 4-methyl-2-pentanone.
- Draw a predicted 13C peaks with chemical shifts of this compound.
- Draw a predicted DEPT 135 spectrum of this compound.
Examples of DEPT Data
Sometimes you will get a series of all DEPT angles for your compound.
For example, here is the DEPT spectra for 4- methyl-2-pentanone.
- Which carbon is represented by the only peak in the DEPT 90?
- Which carbon is represented by the peak is pointing down in the DEPT 135?
- What peak is missing compared to the 13C NMR?
Often, you will only get the DEPT 135.
- Why do you think that people often only obtain the DEPT 135?
DEPT Application Problems
Part 1. Propose a structure for these compounds based on the molecular formula and the 13C spectra.
a. C8H10
b. C10H12O2
c. C5H10
c. C6H10
Practice DEPT & IR Problems
Suggest a structure for a compound that would fit with the spectra and molecular formula given.
1. C6H10O2
2. C6H12O2
