NMR Frequency, Larmor Frequency, or Resonant Frequency

Each NMR-active nuclide resonates at a particular frequency, which is proportional to the magnetic field strength of the spectrometer; the proportionality constant is the magnetogyric ratio. Because of this dependence, it is not possible to give a specific frequency that is characteristic of a nuclide on all instrument systems. However, if a system on which the ¹H nuclide resonates at 100 MHz is taken as a reference point, the NMR frequency for a nucleus X can be calculated by multiplying its frequency factor by the ¹H frequency of the instrument system of interest. Thus, if the factor is 0.2514, as it is for ¹³C, it is trivial to calculate that this nuclide will resonate at around 25.14 MHz on a system whose ¹H frequency is 100 MHz, and at 100.58 MHz on a spectrometer whose ¹H frequency is 400 MHz.