How Do You Determine Proton NMR Shifts?
Proton NMR (nuclear magnetic resonance) shifts incorporate magnetism and quantum physics. Protons respond to a magnetic field with two distinct energies, depending on proton spin direction. An induced magnetic field further influences energy levels. Nearby atoms deplete (de-shield) or add to the influential electron cloud around a given proton. Chemical shift can be calculated in terms of ppm (parts per million). Signals often split because of asymmetrical protons interacting with each other. The area on an NMR graph enclosed by a given NMR signal is proportional to how many protons resonate at a given frequency–therefore, at a given PPM value. Although NMR signals look like vertical lines, they are in fact (narrow) bell curves that enclose a finite area. Understand how protons respond to magnetic fields. Protons aligning with a magnetic field are in a lower energy state than those “facing” it. The concept is similar to swimming with the current–it takes far less energy than swimming
