Carbon-13, DEPT and Coupling Constants · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading carbon spectra and couplings

Science · Chemistry · ages 20-21
Name ______________________   Date ____________

  1. Can carbon peak heights count carbons?

    • Yes, always exactly
    • Only on Mondays
    • No, integrals are unreliable

  2. Why does a routine carbon spectrum show singlets?

    • Proton splitting is removed
    • Carbons never couple
    • The sample holds one carbon

  3. What does a DEPT experiment classify?

    • The solvent brand
    • Each carbon by its attached protons
    • The magnet strength

  4. Cis and trans candidates show couplings of 8 and 15 hertz. Which fits trans?

    • Neither fits anything
    • Both fit both
    • The 15 hertz one

  5. A carbon signal is missing in DEPT but present in the carbon spectrum. What is it?

    • A carbon with no attached protons
    • A broken detector
    • A proton with no carbon

  6. A coupling constant reports on geometry, not just on neighbours.

    Circle one:   True   False

  7. A student counts carbons from carbon peak heights. That reading is safe.

    Circle one:   True   False

  8. Two isomers differ only at one double bond. Carbon data fits both, but one coupling is far larger. How do you rule one out?

    • Assign the larger coupling to trans and discard cis for that bond
    • Discard the carbon spectrum
    • Pick the prettier structure
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Reading carbon spectra and couplings W1-mt_9K6GkAkqq1-s1

  1. No, integrals are unreliable · Heights cannot be trusted for counting in carbon spectra.
  2. Proton splitting is removed · Decoupling collapses each carbon to a single line.
  3. Each carbon by its attached protons · DEPT sorts CH3, CH2, CH, and silent quaternary carbons.
  4. The 15 hertz one · The larger coupling argues for trans geometry.
  5. A carbon with no attached protons · Silent in DEPT plus present in carbon means quaternary.
  6. True · Its size in hertz argues cis against trans.
  7. False · Heights mislead in carbon spectra; count signals and DEPT instead.
  8. Assign the larger coupling to trans and discard cis for that bond · The coupling is the deciding signal when carbon fits both.
Worksheet · LightMySky