Scalar Couplings in Nuclear Magnetic Resonance, General
Nuclear Magnetic Resonance and Electron Spin Resonance Spectroscopy
Published Online: 15 SEP 2006
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
Lee, J. W. 2006. Scalar Couplings in Nuclear Magnetic Resonance, General. Encyclopedia of Analytical Chemistry.
- Published Online: 15 SEP 2006
Indirect spin coupling refers to the magnetic interaction operative between a pair of magnetic nuclei in a molecule that is mediated by bonding electrons. The anisotropic part of this interaction averages out to zero when the internuclear vector connecting the two nuclei randomly changes its orientation in the isotropic fluid state as does the direct magnetic dipolar interaction between the same pair of nuclei which operates through space. The isotropic part, which is usually called the scalar spin coupling, survives such random modulations of the internuclear vector in the fluid state to give rise to splitting of the nuclear magnetic resonance (NMR) lines which would otherwise represent a mere collection of individual absorption lines corresponding to the chemical shift of each constituent spin. Adequate analysis of the multiplet structure of the NMR spectrum arising from a given set of nuclear spins can provide knowledge of the scalar coupling between each pair of nuclear spins which in turn yields a wealth of information on molecular structure as well as molecular processes occurring in the system.