Three Pieces of Information
| Feature | What It Tells You |
|---|---|
| Number of peaks | Number of different hydrogen environments |
| Integration (area) | Ratio of H atoms in each environment |
| Splitting pattern | Number of H atoms on adjacent carbons (n+1 rule) |
The n+1 Splitting Rule
Spin-Spin Splitting
The (n+1) Multiplicity Rule
In high-resolution ¹H NMR, an absorption signal is split into \((n+1)\) sub-peaks, where \(n\) is the number of non-equivalent protons on adjacent carbon atoms (separated by 3 bonds):
- \(n = 0\) → Singlet (ratio 1)
- \(n = 1\) → Doublet (ratio 1:1)
- \(n = 2\) → Triplet (ratio 1:2:1)
- \(n = 3\) → Quartet (ratio 1:3:3:1)
Protons on identical environments do not split each other. O–H protons rarely split adjacent C–H protons due to rapid proton exchange.
Chemical Shift Ranges (δ / ppm)
| Environment | δ / ppm |
|---|---|
| R-CH₃ (alkyl) | 0.9-1.0 |
| R-CH₂-R | 1.2-1.4 |
| R-O-CH (near O) | 3.3-4.3 |
| R-CHO (aldehyde) | 9.4-10.0 |
| R-COOH (acid) | 10.0-12.0 |
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