How does proton magnetic resonance reveal the structure of hydrogen-containing compounds?

Proton magnetic resonance (NMR) spectroscopy is a powerful analytical technique used to determine the structure of hydrogen-containing compounds by exploiting the magnetic properties of the proton. Because protons possess spin, they precess in an applied magnetic field; when irradiated with specific radio frequencies, they undergo resonance absorption.12

The structure of a molecule is revealed through three primary features of the NMR spectrum:

• Chemical Shift: Protons in different local electrical environments—influenced by nearby electrons and electronegative atoms—absorb energy at different frequencies. This shift, measured relative to a reference compound like tetramethylsilane, indicates the chemical nature of the bonds surrounding the hydrogen atoms.312
• Integration: The area under each absorption peak is directly proportional to the number of hydrogen atoms contributing to that signal, allowing chemists to determine the relative ratio of different types of hydrogen in the molecule.31
• Spin-Spin Splitting: Nearby non-equivalent hydrogen atoms cause the absorption peaks to split into multiplets (e.g., triplets or quartets). This pattern provides critical information about the connectivity and proximity of hydrogen atoms within the molecular framework.31

By analyzing these data, chemists can deduce the precise arrangement of atoms within a compound.32