Why should the proton nuclei in different compounds behave differently in the NMR experiment ?

Question

Emilia Alvarez · Accepted Answer

Because the different nuclei in different compounds are in different chemical environments.

The protons (or nuclei) should respond (and do) differently in the NMR experiment if they are in different chemical environments, which implies that they are in different magnetic environments. I can think of 1 example where different nuclei give rise to the the same chemical shift. If your compound has an active hydrogen (i.e. an alcoholic proton or an enolizable proton), it could be replaced by the deuterium isotope, #D#. This hydrogen will no longer appear in the proton NMR spectrum (because it is no longer a proton nucleus). It should appear in the corresponding deuterium NMR spectrum at the same chemical shift. Such labelling studies are relatively easy to perform, especially as deuterium, as heavy water, is dirt cheap.

Carter Allen · Answer

undefined The behavior of proton nuclei in different compounds in NMR experiments is influenced by their chemical environment, which affects their resonance frequency. This is due to the electron distribution around the nuclei, which can shield or deshield the protons, altering their resonance frequencies. Factors such as electronegativity, molecular structure, and nearby functional groups all contribute to these chemical shifts, resulting in different behaviors for proton nuclei in different compounds during NMR experiments.