NMR spectroscopy
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
The topic on one screen
- 13C NMR: the number of peaks = the number of different carbon environments in the molecule.
- 1H NMR: the number of peaks = the number of different proton (hydrogen) environments.
- Chemical shift (delta, in ppm) places each peak; read the fragment it corresponds to straight off the data booklet.
- Integration (1H only): the ratio of peak areas = the ratio of the numbers of H atoms in each environment.
- Splitting (n+1 rule): a peak split into (n+1) lines means n equivalent H atoms on the ADJACENT carbon. A singlet means no H on the neighbouring carbon.
- TMS is the reference (0 ppm): one sharp peak, inert, non-toxic, volatile; the sample is run in a solvent with no 1H (e.g. CDCl3).
Where students actually lose marks
Only about two-thirds linked the number of 13C peaks to the number of carbon environments. It is the most reliable mark in the topic — count the environments, count the peaks, match them.
June 2023 Paper 2 examiner report (Q05.2)
Explaining why a peak is a singlet was well known (M2), but the corresponding structure was harder. Tie the two together: a singlet = no H on the adjacent carbon, and build the structure to fit.
June 2024 Paper 2 examiner report (Q06.4)
The best structure-determination answers analyse each signal systematically; weaker ones reach the right structure but lose marks for not showing how each spectrum feature supports it. Show your reasoning per peak.
June 2022 Paper 2 examiner report (Q06)
Try it — exam-style
The 13C NMR spectrum of a molecule shows 5 peaks. What does this tell you about the molecule?
A peak in a 1H NMR spectrum is split into a quartet (4 lines). What does this tell you about the hydrogens on the adjacent carbon?
In the 1H NMR spectrum of methyl ethanoate (CH3COOCH3) both peaks are singlets. Explain why.
A 1H NMR spectrum has three peaks with an integration ratio of 3 : 2 : 1. State what this ratio represents and suggest which fragment gives the peak integrating to 3.
State two reasons TMS is used as the reference standard in NMR spectroscopy.
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
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