In the 13C spectrum there are 6 carbon peaks (δ 167.35, 132.41, 131.61, 129.03, 61.63 and 14.14 ppm) as we would expect given the top/bottom symmetry in diethyl phthalate. In the DEPT-45 there are only 4 peaks (suggesting two quaternary and 4 with attached protons). There are only 2 peaks in the DEPT-90 spectrum – so we can easily assign the quaternary aromatic-C (132.41 ppm)) and the primary aromatic-C’s (131.61 & 129.03 ppm). Finally, the DEPT-135 obviously distinguishes between the –CH2– (61.63 ppm) and –CH3 (14.14 ppm) of the ethyl chain.
So Cliffnotes, DEPT really simplifies peak assignments for 13C spectra:
1) CH – positive in DEPT-45, DEPT-90 and DEPT-135
2) CH2 – positive in DEPT-45, negative in DEPT-135, not observed in DEPT-90
3) CH3 – positive in DEPT-45 and 135, and are silent in DEPT-90.
DEPT is a great tool to add to your structural elucidation/peak assignment tool box! Happy structure elucidating!
If you would like a concise reminder of the various experiments discussed in this post, please check out our infographic!
References
[1] Jacobsen, N. E. “NMR Spectroscopy Explained: Simplified Theory, Applications and Examples for Organic Chemistry and Structural Biology” 2007, John Wiley & Sons, Inc.: Hoboken, Chapter 7.