Long-Range J Coupling in ¹H NMR

Long-range J coupling in ¹H NMR describes weak interactions between protons that are separated by four or more bonds. These couplings usually have J values below 1 Hz, so they are often too small to appear in a spectrum. When the bonding path includes multiple bonds, however, the coupling can become observable.

Coupling interactions of nuclei across four or more bonds are usually weak and not observed in spectra.

However, multiple bonds along the coupling pathway can result in observable long-range coupling.

In alkenes, allylic and homoallylic couplings are seen across four or five bonds, respectively, where spin information is communicat...