If the energy difference between the a and p spin states of a proton nucleus (AE) depends only on the H NMR magnetogyric ratio(y=2.6753 x 10 radians sec .gauss )and the magnetic field (H), then won,' t all of the protons in a molecule absorb radiation of the exact same energy? Luckily no! We wouldn' t be able to obtain any structural information from a H NMR spectrum if that were the case Remember, nuclei are surrounded by clouds of negatively charged electrons In the presence of an applied magnetic field(Ho), these electrons move in such a way that their motion induces their own small magnetic field (H) At the nucleus, the induced magnetic field(H)opposes the applied magnetic field(Ho). Therefore, the nucleus experiences a magnetic field (H) slightly less than the applied magnetic field (Ho) ced magne e H=H-H applied etic electrons fied(H)∵ This phenomenon is called diamagnetic shielding. Protons with a lot of electron density around them are well-shielded and experience a reduced magnetic field. As a result, there is a smaller energy difference between the two spin states, and lower energy radiation is required to flip the spin from a to p In other words, protons in different electronic environments experience different amounts of shielding and absorb radiation of different frequencies. These differences are referred to as chemical shifts• If the energy difference between the α and β spin states of a proton nucleus (∆E) depends only on the 1 H NMR magnetogyric ratio (γ = 2.6753 x 104 radians·sec–1·gauss–1) and the magnetic field (H), then won't all of the protons in a molecule absorb radiation of the exact same energy? • Luckily, no! We wouldn't be able to obtain any structural information from a 1 H NMR spectrum if that were the case. • Remember, nuclei are surrounded by clouds of negatively charged electrons. In the presence of an applied magnetic field (H0), these electrons move in such a way that their motion induces their own small magnetic field (H'). • At the nucleus, the induced magnetic field (H') opposes the applied magnetic field (H0). Therefore, the nucleus experiences a magnetic field (H) slightly less than the applied magnetic field (H0). 0) 0 induced magnetic field (H') electrons applied magnetic field (H H = H – H' • This phenomenon is called diamagnetic shielding. Protons with a lot of electron density around them are well-shielded and experience a reduced magnetic field. As a result, there is a smaller energy difference between the two spin states, and lower energy radiation is required to flip the spin from α to β. • In other words, protons in different electronic environments experience different amounts of shielding and absorb radiation of different frequencies. These differences are referred to as chemical shifts. 5