2. Basic NMR parameters

The samples on which the NMR experiment is based are made up of atoms, ions or molecules, isolated or assembled. The nuclei are surrounded by an electron cloud and, in most cases, bound to other atoms. For any type of nucleus (e.g. ¹ H), the single line of the isolated nucleus will be replaced by a spectrum of single or multiple lines. The decisive interactions are :

• interaction between nucleus and electronic environment. The associated parameter is the dimensionless screen constant σ ;

• indirect interaction, relayed by bonding electrons, between nuclei separated by a small number of bonds. The associated parameter is the scalar coupling constant J (Hz) ;

• direct interaction between spatially close nuclei. The associated parameter...