Interpret a proton NMR spectrum by combining the number of signals, chemical shift, integration, and splitting pattern to identify proton environments and deduce the molecular structure. This is IB Chemistry HL content in Structure 3.2.
A Systematic Method
Each signal represents a set of chemically equivalent hydrogen atoms. Work through the evidence in a fixed order rather than identifying the compound from one peak.
| Spectrum feature | What it tells you |
|---|---|
| Number of signals | Number of different proton environments, accounting for molecular symmetry |
| Chemical shift, | Electronic environment and likely nearby functional group; values are measured in ppm |
| Integration | Relative number of protons producing each signal |
| Splitting pattern | Number of equivalent protons on adjacent atoms |
Chemical shift increases when a proton is deshielded by an electronegative atom, a carbonyl group, or a nearby pi-electron system. Compare each shift with the characteristic data provided in the IB Chemistry data booklet rather than memorizing every range.
For simple first-order spectra, apply the rule: a proton environment with equivalent neighboring protons is split into peaks. Thus, zero neighbors give a singlet, one gives a doublet, two give a triplet, and three give a quartet.
