Shielding constant and Coupling constant:

i) Shielding constant:  The electrons circulating around the nucleus induce a magnetic field that opposes the applied field or shields the nucleus from the applied field. The shielding constant σ is a measure of the extent of shielding of the nucleus by the electrons around it.

ii) Anisotropy of chemical bond: The chemical shift is dependent on the orientation of the NMR active nucleus with respect to the neighbouring bonds especially the π-bonds. The circular motion of π electrons in the presence of applied magnetic field generates induced magnetic field which opposes the applied field for certain parts of the molecule and for other parts it augments the applied field. This differential field strength of the induced field in different directions is called anisotropy of the bond.

iii) Larmor frequency: When placed in an external field, the magnetic moment of the spinning nuclei interacts with the field and the resulting torque makes the nuclear magnetic moment vector to precess around the direction of the applied field. The frequency of this precession motion is called Larmor frequency.

iv) Coupling constant: The interaction of neighbouring protons in the molecule causes the signals of the interacting protons to split. The magnitude of splitting is proportional to the strength of the interaction. The separation of these peaks in frequency units is called coupling constant and is independent of the strength of the applied magnetic field.