DEPT Practice: Classify Every Carbon
DEPT experiments sort carbons by their attached hydrogens. Here you get the three spectra an organic chemist actually compares: the broadband-decoupled ¹³C spectrum on top, DEPT-90 (CH only), and DEPT-135 (CH and CH₃ up, CH₂ down). Read them against each other and classify every lettered signal as CH₃, CH₂, CH, or quaternary. Note that no structure is shown — DEPT classification is evidence you extract before you know the structure, and that is exactly how it is used in real structure determination.
¹³C spectrum (reconstructed from experimental data)
DEPT-90 — CH only
DEPT-135 — CH/CH₃ up, CH₂ down
Common Questions
Why do quaternary carbons disappear in DEPT spectra?
DEPT builds its signal by transferring polarization from attached hydrogens to the carbon. A carbon with no attached hydrogen has nothing to transfer from, so it gives no DEPT signal at all. That absence is useful information: a line that appears in the plain ¹³C spectrum but in neither DEPT spectrum must be a quaternary carbon (or a carbonyl with no attached H).
How do I tell CH from CH₃ when both point up in DEPT-135?
Use DEPT-90, which shows only CH carbons. A signal that points up in DEPT-135 and also appears in DEPT-90 is a CH; a signal that points up in DEPT-135 but is absent from DEPT-90 is a CH₃. CH₂ carbons need no tiebreak — they are the ones pointing down in DEPT-135.
Why are quaternary carbon peaks so short in the regular ¹³C spectrum?
Two reasons: quaternary carbons relax slowly, so they recover less magnetization between scans, and they gain little NOE enhancement because the NOE comes from decoupling nearby attached protons. Both effects shrink the peak. The reconstructed spectra here draw quaternary lines short on purpose to match what you see on a real spectrometer.
Reconstructed from published data: assigned shifts from nmrshiftdb2 (CC BY-SA 4.0) · DEPT panels derived from each carbon's attached-H count.