1H NMR Chemical Shift Calculator
Look up expected 1H NMR chemical shifts for common functional group environments.
What Determines Chemical Shift
A proton's resonance position depends on the electron density around it. Electrons shield the nucleus from the applied field, so electron-rich protons resonate upfield at low ppm. Anything withdrawing electron density deshields the proton and shifts it downfield.
| Environment | δ (ppm) | Why |
|---|---|---|
| TMS reference | 0 | Highly shielded by silicon |
| Alkane CH3 | 0.9 | Baseline |
| Allylic / next to C=O | 2.0–2.7 | Mild deshielding |
| Next to O (ether, ester) | 3.3–4.5 | Strong electronegativity effect |
| Vinyl | 4.5–6.5 | sp² plus anisotropy |
| Aromatic | 6.5–8.5 | Ring current — not just electronegativity |
| Aldehyde | 9.5–10.5 | Carbonyl plus anisotropy |
| Carboxylic acid | 10–13 | Strongest deshielding |
Aromatic protons deserve special mention. They appear far downfield not because of electronegativity but because of the ring current: circulating π electrons generate a local magnetic field that reinforces the applied field at the ring edge. Protons above an aromatic ring experience the opposite and appear unusually upfield — sometimes at negative ppm.
Multiplicity and Coupling
The n+1 rule: a proton with n equivalent neighbours appears as n+1 peaks. Three neighbours give a quartet, two give a triplet. Intensities follow Pascal's triangle — 1:2:1 for a triplet, 1:3:3:1 for a quartet.
The coupling constant J, measured in hertz, is independent of field strength — unlike chemical shift in ppm, which is deliberately field-independent but appears at different hertz values on different instruments. J values are diagnostic of geometry: typical vicinal coupling is 6–8 Hz, while trans alkene coupling reaches 12–18 Hz and cis is 6–12 Hz.
Worked Examples
Common Mistakes
The dominant effect is the ring current from circulating π electrons, not inductive withdrawal. This is why protons above a ring appear upfield instead.
The n+1 rule applies to equivalent neighbours. Different neighbours with different J values produce more complex multiplets.
Exchangeable protons often appear as broad singlets because rapid exchange averages out the coupling. Their shift also varies with concentration and solvent.
Chemical shift in ppm is field-independent, which is why it is used. Coupling constants in hertz are also field-independent, but the same peak separation in hertz corresponds to different ppm on different instruments.
Frequently Asked Questions
Formula Explorer connections
Interpretation: This analytical relationship converts an instrument signal, separation measure or optical response into concentration, identity or performance. Assumption: Calibration, blank correction, linear range, path length, matrix effects and instrument settings must match the sample and method.