NMR Spectra: Counting Environments · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Counting neighbours in NMR

Science · Chemistry · ages 17-18
Name ______________________   Date ____________

  1. A proton spectrum shows one signal split into 2 lines and one split into 7 lines, in the ratio 6 to 1. Which fragment fits?

    • (CH3)2CH
    • CH3CH2
    • CH3CH2CH2

  2. A carbon 13 spectrum shows 3 signals. How many carbon environments does the molecule have?

    • 1
    • 3
    • 6

  3. TMS is the inert reference whose single peak defines zero on the NMR scale.

    Circle one:   True   False

  4. Hydrogens with 2 neighbours on the next carbon split into how many lines?

    Answer: ______________

  5. In an ethyl group, CH3CH2, why is the CH2 signal a quartet?

    • It has 3 neighbours on the CH3
    • It has no neighbours at all
    • It sits in a deuterated solvent

  6. Why is the NMR solvent deuterated?

    • To add extra proton peaks
    • To avoid swamping the sample signal
    • To shift TMS away from zero

  7. Where does the triplet and quartet splitting come from in an ethyl group?

    • Carbon 13 isotopes in the solvent
    • The TMS reference wobbling
    • Neighbour hydrogens coupling across carbons

  8. A student predicts a singlet for CH3 sitting next to CH2. What is wrong?

    • The CH3 has 2 neighbours, so it must split
    • Singlets only appear in carbon spectra
    • TMS blocks all singlets
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Answer key

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

Counting neighbours in NMR W1-mt_JquoiaxOMu-s1

  1. (CH3)2CH · Six equivalent CH3 hydrogens with 1 neighbour give 2 lines, and one CH hydrogen with 6 neighbours gives 7 lines: (CH3)2CH.
  2. 3 · Each set of equivalent carbons gives exactly one signal.
  3. True · Every shift is measured away from the TMS zero.
  4. 3 · Two plus one gives 3 lines, a triplet.
  5. It has 3 neighbours on the CH3 · Three neighbours split a signal into four lines.
  6. To avoid swamping the sample signal · Deuterium gives no proton signal where your sample reads.
  7. Neighbour hydrogens coupling across carbons · Splitting records how many hydrogens sit on the neighbouring carbon.
  8. The CH3 has 2 neighbours, so it must split · Hydrogens on the next carbon split the signal, so a singlet for that CH3 breaks the n plus one rule.
Worksheet · LightMySky