Counting neighbours in NMR

Science · Chemistry · ages 17-18

Name ______________________ Date ____________

A proton spectrum has a triplet and a quartet in the ratio 3 to 2. Which fragment fits?
- CH3 CH2
- CH3 CH3
- CH2 CH2
A carbon 13 spectrum shows 3 signals. How many carbon environments does the molecule have?
- 1
- 3
- 6
TMS is the inert reference whose single peak defines zero on the NMR scale.
Circle one: True False
Hydrogens with 2 neighbours on the next carbon split into how many lines?
Answer: ______________
In that ethyl pattern, 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
Why is the NMR solvent deuterated?
- To add extra proton peaks
- To avoid swamping the sample signal
- To shift TMS away from zero
Where does the triplet quartet splitting come from in ethyl?
- Carbon 13 isotopes in the solvent
- The TMS reference wobbling
- Neighbour hydrogens coupling across carbons
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

Answer key

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

CH3 CH2 · Only ethyl gives 3H against 2H with that triplet quartet pair.
3 · Each set of equivalent carbons gives exactly one signal.
True · Every shift is measured away from the TMS zero.
3 · Two plus one gives 3 lines, a triplet.
It has 3 neighbours on the CH3 · Three neighbours split a signal into four lines.
To avoid swamping the sample signal · Deuterium gives no proton signal where your sample reads.
Neighbour hydrogens coupling across carbons · Splitting records how many hydrogens sit on the neighbouring carbon.
The CH3 has 2 neighbours, so it must split · Neighbours always split, so a singlet there breaks the n plus one rule.