In Magnetic resonance, nuclei with spin angular momentum other than zero are used, such as $^1H$ and $^{13}C$. However, the resonance frequencies are not the same for all hydrogen or carbon nuclei, they depend on the chemical environment that surrounds each nucleus. This is due to the fact that the electrons surrounding each nucleus generate a magnetic field that opposes the applied one, it is said that the nuclei are shielded, where $\sigma$ is the shielding constant. \begin{equation}\label{ec11} B_{eff}=B_0-\sigma B_0=(1-\sigma)B_0 \end{equation} $B_{ef}$ is the net magnetic field acting on the proton; $B_0$ is the applied magnetic field; $\sigma$ is the screening constant, independent of the applied field. Under this new situation, with the nuclei shielded by the surrounding electron density, the resonance frequency becomes \begin{equation}\label{ec12} \nu=\frac{\gamma}{2\pi}(1 -\sigma)B_0 \end{equation} Nuclei with different chemical environments have a different screening constant, generating different signals in the NMR spectrum.