Coupling of Protons to Other Important Nuclei

Coupling of 13C to several other nuclei, the most important of which are 3IP, 19F, and 2D, may be observed in proton-decoupled spectra. Representative coupling constants are given in Table 4.3. 

The coupling of nuclear spin to electron spin by the Fermi contact interaction is most important for proton spins, but it is not necessarily the most important mechanism for other nuclei. These nuclei may also interact by a dipolar mechanism with the electron magnetic moments and with their orbital motion, and there is no simple way of specifying whether / will be positive or negative. 

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