Indirect or scalar coupling

Indirect or scalar coupling of nuclear spins through covalent bonds causes the splitting of NMR signals into multiplets in high-resolution NMR spectroscopy in the solution state. The direct or... 

The scalar coupling (also called spin-spin, indirect or J-coupling) is a quantum mechanical-based indirect interaction of nuclear moments mediated via the electrons... 

Detection of the NMR spectrum of an organic compound in solution with the single pulse experiment, as described above, is quite feasible. However, were the spectrum acquired in this manner, one would notice that the number of peaks in it exceeds the number of unique carbon environments. Most organics contain protons as well as carbon atoms. These protons are coupled to the carbons through the indirect (or scalar) J coupling, resulting in splitting of the carbon resonances of any carbon with attached protons. 

While the terminology scalar relaxation of the first kind concerns J modulation (J spin spin or scalar or indirect coupling constant) by exchange phenomena, the usual example of the second kind is a spin 1/2 nucleus (7), J coupled to a fast relaxing quadrupolar nucleus (S) with relaxation times Tj and Tf (and spin number /s)- The relevant interaction is of the form... 

In many cases the inorganic chemist will be interested in the NMR spectrum of a nuclide of low sensitivity (denoted S or indirectly detected spin) in a compound containing a high-sensitivity nucleus (denoted I or detector spin). If scalar coupling exists between the two nuclides, then the 2D HMQC and HSQC techniques offer an alternative to direct observation. The distinction between HMQC and HSQC is that TS -magnetization is stored as either multiple... 

In some cases, when a spin-1/2 nucleus such as P, or is coupled to a quadrupolar nucleus, the simulation by a computer program of the unusual lineshape of the spin-1/2 may provide information about the chemical shift anisotropy, the quadrupole coupling constant and the indirect scalar spin-spin coupling constant involving the metal atom. This method has been applied to the P spectra of phosphines bound to cobalt in heteronuclear clusters [17]. 

The coupling mechanism we discussed in this section is known under the following alternative names Spin-spin coupling, Scalar coupling, J-coupling, or Indirect coupling. 

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