Chemical Shift Calculator

Calculator

Calculation mode Chemical shift from sample and reference frequencies Frequency offset from chemical shift (ppm) Sample frequency from chemical shift and reference frequency

Tip: Use the mode that matches what your spectrum reports.

Spectrometer frequency (nu0)

Enter in MHz (e.g., 400, 500, 600).

Sample frequency (nusample)

Hz kHz MHz

Use the same unit as your peak list.

Reference frequency (nuref)

Hz kHz MHz

Often the internal standard reference line.

Submit Reset

Example data table

Illustrative values for a 400 MHz instrument.

Formula used

Chemical shift is reported in parts per million (ppm) to remove field dependence:

• nusample is the measured sample resonance frequency.
• nuref is the reference resonance frequency (standard).
• nu0 is the spectrometer frequency for that nucleus.

How to use this calculator

1. Select the calculation mode that matches your data source.
2. Enter the spectrometer frequency in MHz (e.g., 400).
3. Provide sample and reference frequencies, or enter delta in ppm.
4. Press Submit to display results directly under the header.
5. Use the CSV/PDF buttons to save results for documentation.

Professional notes on chemical shift calculations

1) What chemical shift represents

Chemical shift describes how the local electronic environment changes a nucleus’s resonance relative to a standard. Shielding moves the resonance upfield, while deshielding moves it downfield. Reporting shift in ppm makes the value comparable across instruments with different magnetic fields.

2) Reference standards and the zero point

The reference line sets the zero position on the chemical shift scale. In many proton experiments, an internal or external standard establishes the reference frequency. The calculator treats the reference as nuref, so the sign of the shift depends on whether the sample peak is above or below that reference frequency.

3) Using frequency differences effectively

Instruments measure frequencies, but spectra are annotated in ppm. The essential step is computing dnu = nusample − nuref. Once dnu is known in hertz, converting to ppm is a scaling operation by nu0. This approach helps when peak picking provides absolute frequencies or when you compare offsets between peaks.

4) Selecting the correct spectrometer frequency

nu0 is the operating frequency for the observed nucleus on your system, commonly entered as 400, 500, or 600 MHz. For other nuclei, nu0 differs and should match the channel used during acquisition. A wrong nu0 scales every ppm value, so confirm it from the experiment header.

5) Interpreting positive and negative shifts

Depending on the referencing convention and the nucleus, shifts can be positive or negative. Negative values often indicate upfield resonances relative to the reference. When comparing datasets, keep the same referencing method and note any digital referencing corrections applied by processing software.

6) Unit handling and conversions

Peak lists may report frequencies in Hz, kHz, or MHz. The calculator converts inputs to Hz internally, then reports both Hz and kHz for the offset. This dual reporting is useful because linewidths and couplings are often discussed in Hz, while offsets may be convenient in kHz for high-field instruments.

7) Quality checks and common pitfalls

If results look too large, check that you did not enter MHz values into a Hz field. Also verify that the reference frequency corresponds to the same nucleus and the same acquisition. For floating references, measure the reference peak each run to avoid systematic drift in chemical shift reporting.

8) Reporting and documentation workflows

Exporting calculated values helps with lab notebooks, method validation, and cross-team review. Use CSV for spreadsheets or pipelines, and PDF for attachments in reports. Store the mode, nu0, and your reference choice together so future comparisons remain traceable and reproducible.

FAQs

1) Why is chemical shift reported in ppm?

ppm removes dependence on magnetic field strength, so the same compound can be compared across instruments. It is a normalized frequency difference relative to the spectrometer frequency.

2) What value should I use for nu0?

Use the operating frequency for the nucleus you observed, typically shown in the experiment header (for example 400 MHz for many proton systems). Enter it in MHz in the form.

3) Can the shift be negative?

Yes. A negative value can occur when the sample resonance is upfield relative to the reference under your referencing convention. Keep conventions consistent when comparing datasets.

4) Which reference frequency should I enter?

Enter the reference peak frequency used to define the chemical shift scale for that spectrum. If your software applies digital referencing, use the referenced peak position it reports.

5) I only have ppm values, not frequencies. What should I do?

Choose the “Frequency offset from chemical shift” mode to convert ppm to an offset in Hz and kHz for your instrument. You do not need absolute frequencies in that mode.

6) How precise are the results?

The calculation is exact for the numbers you enter. Practical precision depends on peak picking, referencing quality, temperature stability, and the accuracy of the spectrometer frequency.

7) Does this apply to nuclei other than hydrogen?

Yes. The same ppm definition applies broadly, but you must use the correct nu0 for that nucleus and a suitable reference standard used in your experiment.