DEPT (Distortionless Enhancement by Polarization Transfer)
NMR spectroscopy is a technique used in nuclear magnetic resonance (NMR)
spectroscopy to provide information about the types of protons (hydrogen atoms)
directly bonded to carbon atoms in a molecule. DEPT is especially valuable for
determining the presence and multiplicity of proton environments in carbon-13
(^13C) NMR spectra.
The primary goal of DEPT NMR spectroscopy is to
differentiate between carbon environments that are directly bonded to zero,
one, two, or three protons. It achieves this by applying polarization transfer
techniques during the NMR experiment, resulting in distinctive spectral
features. DEPT spectra are often easier to interpret compared to conventional
^13C NMR spectra, which directly observe carbon nuclei without information
about their proton environment.
There are three common types of DEPT NMR experiments:
DEPT-90, DEPT-135, and DEPT-135 with decoupling (DEPTQ):
- DEPT-90:
In DEPT-90, carbon signals that are directly bonded to at least one proton
appear as positive peaks, while carbon signals without directly bonded
protons appear as suppressed or negative peaks. This allows
differentiation between quaternary carbons (C), methine carbons (CH), and
methylene carbons (CH2).
- DEPT-135:
DEPT-135 provides similar information as DEPT-90 but with increased
sensitivity to quaternary carbons. In DEPT-135, quaternary carbons appear
as positive peaks, methine carbons as positive peaks, and methylene
carbons as suppressed peaks.
- DEPTQ:
DEPTQ (DEPT-135 with decoupling) combines DEPT-135 with proton decoupling
during acquisition, resulting in sharp peaks for all carbon types. This
makes it easier to distinguish between different carbon environments.
In summary, DEPT NMR spectroscopy is a powerful tool for
extracting valuable information about the types of protons directly bonded to
carbon atoms in a molecule. By providing insights into the proton-carbon
connectivity, DEPT spectra aid in the determination of molecular structure and
the identification of functional groups in complex organic molecules.