page_title: J-coupling
section_title: Vector model and manifestations for chemical structure assignments
hierarchical_section_title: J-coupling / Vector model and manifestations for chemical structure assignments
caption_attribution_description: English: energy diagram illustrating J-coupling (probably will be improved and replaced in near future)
context_page_description: In nuclear chemistry and nuclear physics, Scalar or J-couplings are mediated through chemical bonds connecting two spins. It is an indirect interaction between two nuclear spins which arises from hyperfine interactions between the nuclei and local electrons. In NMR spectroscopy J-coupling contains information about relative bond distances and angles. Most importantly, J-coupling provides information on the connectivity of chemical bonds. It is responsible for the often complex splitting of resonance lines in the NMR spectra of fairly simple molecules.
  J-coupling is a frequency difference that is not affected by the strength of the magnetic field, so is always stated in Hz.
context_section_description: The origin of J-coupling can be visualized by a vector model for a simple molecule such as hydrogen fluoride (HF). In HF, the two nuclei have spin . Four states are possible, depending on the relative alignment of the H and F nuclear spins with the external magnetic field. The selection rules of NMR spectroscopy dictate that ΔI = 1, which means that a given photon (in the radio frequency range) can affect ("flip") only one of the two nuclear spins.
   
  J-coupling provides three parameters: the multiplicity (the "number of lines"), the magnitude of the coupling (strong, medium, weak), and the sign of the coupling.
caption: Energy diagram showing the effects of J-coupling for the molecule hydrogen fluoride.
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