The presence of a magnetic field can significantly affect the energy levels and magnetic properties of a molecule. This influence can be observed through the changes in magnetic susceptibility and nuclear magnetic resonance NMR parameters.1. Magnetic susceptibility: Magnetic susceptibility is a measure of how a substance responds to an external magnetic field. When a molecule is placed in a magnetic field, its electrons can either be diamagnetic opposing the applied field or paramagnetic aligning with the applied field . The presence of a magnetic field can cause changes in the energy levels of the electrons, leading to a shift in their distribution. This shift can result in an alteration of the magnetic susceptibility of the molecule. In general, molecules with unpaired electrons e.g., radicals or transition metal complexes exhibit higher magnetic susceptibility due to their paramagnetic nature.2. Nuclear magnetic resonance NMR parameters: NMR is a powerful technique used to study the magnetic properties of atomic nuclei in a molecule. The presence of a magnetic field affects the energy levels of the nuclei, leading to changes in their resonance frequencies. This effect is known as the Zeeman effect. The energy level splitting depends on the strength of the magnetic field and the magnetic properties of the nucleus e.g., its magnetic moment and spin quantum number .In NMR spectroscopy, the chemical shift is a crucial parameter that provides information about the electronic environment surrounding a nucleus. The presence of a magnetic field can cause changes in the electron distribution around the nucleus, which in turn affects the shielding of the nucleus from the external magnetic field. This change in shielding leads to variations in the chemical shift values.Additionally, the presence of a magnetic field can also influence other NMR parameters such as coupling constants which provide information about the interaction between nuclei and relaxation times which are related to molecular motion and dynamics .In summary, the presence of a magnetic field can significantly affect the energy levels and magnetic properties of a molecule, leading to changes in magnetic susceptibility and NMR parameters. Understanding these effects is essential for the accurate interpretation of experimental data and the development of theoretical models to describe molecular behavior in the presence of magnetic fields.