ABSTRACT
Commonly, nuclear spins in a sample placed into external magnetic eld B0 for observation of NMR are not isolated. They are capable of interacting with their environments. These interactions can be with the same or different types of nuclei and with electrons, which can be paired or unpaired. Interactions with the closest environments through chemical bonds or through space give rise to the phenomena of chemical shift, spin-spin coupling (homonuclear and heteronuclear), quadrupolar coupling, and dipolar coupling. Independently of the objects and their nature-a solution or a solid (crystalline or amorphous, homogeneous or heterogeneous)— chemical shifts and internuclear couplings are always a focus of researchers as they are the main factors affecting NMR spectra, along with the number of resonances and their line shapes. These parameters should be decoded in structural terms by application of the relevant relationships: spectrum/chemical structure, chemical shift/electron distribution, splitting/neighboring spins, etc., which can be rationalized on the basis of the theoretical considerations presented in this chapter.
