16.23: 16-6 DEPT ¹³C NMR Spectroscopy

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Distortions Enhancement by Polarization Transfer (DEPT)

DEPT is used for distinguishing between a CH₃ group, a CH₂ group, and a CH group. The proton pulse is set at 45°, 90°, or 135° in the three separate experiments. The different pulses depend on the number of protons attached to a carbon atom. Fig 11. is an example about DEPT spectrum.

Fig 11. DEPT spectrum of n-isobutlybutrate

While broadband decoupling results in a much simpler spectrum, useful information about the presence of neighboring protons is lost. However, another modern NMR technique called DEPT (Distortionless Enhancement by Polarization Transfer) allows us to determine how many hydrogens are bound to each carbon. For example, a DEPT experiment tells us that the signal at 171 ppm in the ethyl acetate spectrum is a quaternary carbon (no hydrogens bound, in this case a carbonyl carbon), that the 61 ppm signal is from a methylene (CH₂) carbon, and that the 21 ppm and 14 ppm signals are both methyl (CH₃) carbons. The details of the DEPT experiment are beyond the scope of this text, but DEPT information will often be provided along with ¹³C spectral data in examples and problems.

Below are two more examples of ¹³C NMR spectra of simple organic molecules, along with DEPT information.