NMR coupling constant ($J$)

The frequency spacing $J$ of a first-order multiplet, expressed in hertz. For a spectrum at ${\nu }_0$ MHz, $J/\mathrm{Hz}=(\Delta \delta /\mathrm{ppm})({\nu }_0/\mathrm{MHz})$. A bond-count superscript, such as ${}^{3}J$, specifies the coupling path.