Interpret AQA proton NMR using hydrogen environments, integration ratios and simple singlet, doublet, triplet and quartet patterns.
Three questions for each signal
Ask: where is the signal, how much area does it have, and how is it split? Chemical shift suggests the local environment; integrated area gives the relative number of hydrogens; splitting gives information about neighbouring inequivalent hydrogens. These are different pieces of evidence.
A triplet is one signal split into three lines, not three different hydrogen environments. Peak height is not integration: use the area or the given integration trace. Equivalent protons contribute to the same signal and do not split one another in the simple model.
Read proton shifts with the supplied table
Hydrogens on carbons near electronegative atoms or electron-withdrawing groups often occur at larger δ than ordinary alkyl hydrogens. Use the specific environment and the supplied ranges rather than saying that every CH3 has the same shift.
| Environment | Range |
|---|---|
| RCH3 | 0.7–1.2 |
| R2CH2 | 1.2–1.4 |
| R3CH | 1.4–1.6 |
| C–H on carbon adjacent to C=O | 2.1–2.6 |
| C–H in R–O–C–H | 3.1–3.9 |
| CH2 bonded to Cl or Br | 3.1–4.2 |
| C–H in RCOO–C–H | 3.7–4.1 |
| Alkene C–H | 4.5–6.0 |
| Aldehyde –CHO | 9.0–10.0 |
| Carboxylic acid –COOH | 10.0–12.0 |
| Alcohol OH | 0.5–5.0 |
| Amine NH2 | 1.0–4.5 |
Turn relative areas into hydrogen counts
Original example: an unknown with eight hydrogens has three integrations 1.5 : 1.0 : 1.5. Divide by 0.5 to obtain 3 : 2 : 3. These account for all eight hydrogens. A ratio of 3 : 2 : 3 alone does not tell you which signal is next to oxygen: use the shifts.
Integration values may already represent numbers of hydrogens, or may be arbitrary relative areas. Use the molecular formula to choose the scale. Exchangeable OH/NH signals can be broad or give less reliable areas in real samples; follow the information provided.
The n + 1 rule and its limits
For the simple aliphatic examples in this course, a set of protons coupled to n equivalent neighbouring protons on an adjacent carbon is split into n + 1 lines. Count the neighbouring hydrogens, not the hydrogens in the signal you are assigning.
If neighbouring protons form different sets, the pattern can be more complicated than one n + 1 multiplet. Do not add unlike sets blindly. Proton exchange often removes observable coupling to OH or NH hydrogens, so they are usually treated as unsplit in the standard A-Level examples; this is condition-dependent rather than a universal law.
| Equivalent neighbouring H | Pattern | Ideal relative line intensities |
|---|---|---|
| 0 | Singlet | 1 |
| 1 | Doublet | 1 : 1 |
| 2 | Triplet | 1 : 2 : 1 |
| 3 | Quartet | 1 : 3 : 3 : 1 |
Diagram placeholder
Diagram placeholder — four simple proton multiplets
Labels to include:
- Singlet: one line
- Doublet: two lines of equal ideal intensity
- Triplet: three lines with 1:2:1 ideal intensity
- Quartet: four lines with 1:3:3:1 ideal intensity
- Bracket each whole multiplet as one environment
- Integration refers to the total area of that bracket
Draw separated model patterns at arbitrary shifts, explicitly labelled as schematic. Do not make the number of lines look like the number of different environments.
Worked assignment: ethyl ethanoate
Ethyl ethanoate is CH3COOCH2CH3. It has three proton environments with integration 3 : 2 : 3. These idealised teaching shifts and patterns are mutually consistent with the structure.
A quartet and triplet with areas 2 : 3 support an ethyl fragment, but the quartet’s shift indicates what the CH2 is attached to. In ethyl ethanoate it is bonded to the ester oxygen. In methyl propanoate, CH3CH2COOCH3, the CH2 is beside C=O instead. Those molecules share a formula and the same broad pattern count but have different assignments.
| Group | Approximate δ / ppm | Integration and pattern | Reason |
|---|---|---|---|
| CH3–C=O | 2.1 | 3 H, singlet | The adjacent carbonyl carbon has no H |
| –O–CH2–CH3 | 4.1 | 2 H, quartet | The neighbouring CH3 has three equivalent H |
| –CH2–CH3 | 1.2 | 3 H, triplet | The neighbouring CH2 has two equivalent H |
OH signals and alcohol examples
For ethanol in the usual simplified spectrum, CH3 gives a triplet, CH2 a quartet and OH an often broad, unsplit signal. The areas are 3 : 2 : 1. Do not count the OH proton when predicting the usual CH2 quartet under rapid exchange conditions.
As an optional diagnostic extension, adding D2O can make an exchangeable OH or NH proton signal disappear because hydrogen is exchanged for deuterium. This does not remove the carbon-bound proton signals and does not on its own distinguish every OH-containing functional group.
Propan-2-ol has a six-hydrogen methyl doublet because both equivalent methyl groups neighbour the same CH. Its CH multiplet is more complex than the quartet limit used in the basic AQA exercises; do not mislabel it as a triplet merely because it is next to two carbon atoms.
Tie each explanation to the correct observation
AQA June 2023 Paper 2 Q05.4 separately assesses splitting and shift reasoning. “Two hydrogens” explains an integration of 2, while “three neighbouring hydrogens” explains a quartet. Neither is a substitute for identifying the oxygen-related environment that causes a shift near 4 ppm.
When the data lack integration or contain overlapping multiplets, state the resulting limitation rather than inventing missing information. Q05.6 and the associated report make this distinction in a specific spectrum.
Quick checks
Original Finesse questions. Reveal the indicative worked solutions after attempting each question; these are not official AQA mark allocations.
Q1. A signal integrates to 3 H and is a doublet. What do the area and splitting tell you separately?Show answer
The signal represents three equivalent hydrogens. In the simple n + 1 model, the doublet indicates coupling to one neighbouring hydrogen.
Q2. Why is the CH3CO signal of ethyl ethanoate a singlet?Show answer
The adjacent carbonyl carbon has no attached hydrogen. The three hydrogens within that methyl group are equivalent and do not split one another.
Q3. Integrations are 6 : 4 : 6 and the molecule has eight hydrogens. Convert the integrations to H counts.Show answer
Divide each integration by 2 to obtain 3 : 2 : 3, which sums to eight.
Q4. Why does a 2 H quartet near 4.1 ppm support OCH2CH3 more strongly than CH2CH3 alone?Show answer
The quartet and area support CH2 next to CH3. Its larger chemical shift additionally supports CH2 attached to oxygen, in the appropriate ester range.
Q5. Does every OH hydrogen always give a sharp singlet at the same shift?Show answer
No. Exchange and hydrogen bonding affect its width, position and sometimes coupling. An unsplit OH signal is a useful standard model, not an unconditional rule.
Sources
Sources and examiner guidance (reviewed 2 October 2026)
- AQA 7405 organic chemistry specification — 3.3.15 coverage and required skills.
- Chemrevise: NMR Spectroscopy — Coverage checklist; explanations, data exercises and quick checks on this page are original Finesse material.
- AQA June 2023 Paper 2 mark scheme — Q05 (pp22–24) and examiner report p4: environments, shift versus splitting, overlap and missing integration.
- AQA June 2023 Paper 2 examiner report — Read alongside the question-specific marking guidance; not a universal wording checklist.
- AQA June 2022 Paper 2 mark scheme — Q06.1 (p25) and report pp5–6: coherent combined IR, 1H and 13C interpretation.
- AQA June 2022 Paper 2 examiner report — Read with the matching question context described in the mark-scheme source.
- AQA Chemistry data booklet — Page 3: infrared and NMR ranges. Worked spectra here use original, idealised teaching data.
Finesse Tuition is not endorsed by AQA or Chemrevise. All explanations and examples here are our own.