Chemical shift normalizes frequency displacement; the corresponding hertz separation changes with the frequency basis.
Keep the reference in chemical shift
NMR chemical shift expresses a frequency difference relative to a reference frequency, commonly displayed in parts per million. The reference convention belongs to the reported value. A displacement on the ppm axis and a displacement in hertz are related quantities rather than identical numbers. Primary reference: IUPAC: chemical shift.
When the frequency basis is expressed in MHz, multiplying a ppm displacement by that MHz value gives the corresponding hertz displacement. This numerical convenience follows the factors of one million. It does not eliminate the need to state the frequency basis or reference.
Calculate an original field-basis pair
For a fictional signal located 2 ppm from its reference, a 400 MHz basis gives a frequency displacement of 800 Hz. A 600 MHz basis gives 1200 Hz for the same 2 ppm displacement. The normalized coordinate remains 2 ppm while its hertz displacement changes.
Conversely, a fixed 800 Hz difference is 2 ppm at 400 MHz but about 1.33333 ppm at 600 MHz. These are coordinate calculations, not claims that every sample retains the same shift under changed conditions or that a new spectrometer produces a specific chemical observation.
Build a frequency-reference worksheet
Enter reference identity, frequency basis in MHz, measured difference in Hz, calculated ppm and the sign convention. Recalculate one result using the dimensionless ratio before applying the million multiplier. Keep absolute frequencies distinct from their differences.
When comparing spectra, inspect the reference and sample conditions rather than comparing unlabeled numbers. A chemical-shift value can contribute to interpretation but cannot establish a structure alone. This worksheet concentrates on the frequency normalization and makes no assignment, purity determination or instrument capability claim.
Customer Questions
What is 2 ppm at 400 MHz?
Its defined displacement is 800 Hz.
Is 800 Hz always 2 ppm?
The frequency basis affects the conversion.
Does this arithmetic assign a structure?
It only converts a defined coordinate.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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