Calculator Inputs
Formula Used
When the frequency difference is entered in Hz and the spectrometer frequency is entered in MHz, the formula directly returns chemical shift in ppm.
Use this equivalent form when sample, reference, and carrier frequencies are all handled in the same absolute frequency unit.
This shielding relation is an approximation. It is useful for quick comparisons when a reference shielding value is already known.
How to Use This Calculator
- Select the calculation mode that matches your available data.
- Choose the nucleus or enter a custom label.
- Enter the spectrometer frequency in MHz.
- Provide sample and reference frequencies, an offset, or a target ppm value.
- Optionally add uncertainties and reference shielding for deeper analysis.
- Press the calculate button to view the result, graph, and export options.
Example Data Table
| Nucleus | Spectrometer (MHz) | Reference (MHz) | Sample (MHz) | Offset (Hz) | Shift (ppm) |
|---|---|---|---|---|---|
| 1H | 400.0000 | 400.130000 | 400.132850 | 2850 | 7.1250 |
| 13C | 100.0000 | 100.620000 | 100.633500 | 13500 | 135.0000 |
| 19F | 376.5000 | 376.200000 | 376.196235 | -3765 | -10.0000 |
| 31P | 161.9000 | 161.000000 | 161.001619 | 1619 | 10.0000 |
Frequently Asked Questions
1. What does chemical shift measure?
Chemical shift measures how far a nucleus resonates from a chosen reference signal. It reflects local electronic shielding and is usually reported in parts per million.
2. Why is ppm used instead of absolute frequency?
PPM normalizes the shift to spectrometer frequency. That makes values easier to compare across instruments with different field strengths.
3. What sign convention does this tool use?
The calculator uses sample minus reference. A positive result means the sample frequency is above the reference. A negative result means it is below the reference.
4. Can I calculate shift from offset only?
Yes. Choose the offset mode, enter the offset and spectrometer frequency, and the calculator converts that offset directly into ppm.
5. What does the shielding estimate represent?
It gives an approximate sample shielding value using the relation σsample ≈ σreference − δ. Use it for quick comparisons, not rigorous ab initio analysis.
6. Why can my result be negative?
A negative result appears when the sample resonance lies upfield from the reference under the selected sign convention. That is physically reasonable in many systems.
7. How is uncertainty estimated here?
The tool combines sample and reference frequency uncertainties in quadrature, then divides by spectrometer frequency to estimate uncertainty in ppm.
8. Can I export the calculated results?
Yes. After calculation, use the CSV button for spreadsheet-friendly output or the PDF button for a compact report you can save or share.