J, or scalar, coupling

One particular type of internuclear coupling is called J, or scalar, coupling. Such couplings are prominent features of ¹H spectra, leading to splittings which provide clues to the structure of the sample. However, they can be difficult to interpret, particularly if signal overlap becomes a problem. ¹³C data are usually presented as decoupled spectra, in which ¹H-¹³C interactions have been removed by irradiation at the ¹H frequency. The distance between any two peaks in a J-split multiplet is called the coupling constant, J_XY, where X and Y indicate the coupled nuclides. The coupling constant, usually given in Hz, is independent of magnetic field, so overlap is reduced at higher fields.