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How does nuclear magnetic resonance spectroscopy use radio waves and magnetic fields?

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Nuclear magnetic resonance (NMR) spectroscopy utilizes magnetic fields and radio waves to analyze the molecular structure of substances by interacting with specific atomic nuclei that possess magnetic properties.12

The Role of Magnetic Fields

When a sample is placed in a powerful, stationary magnetic field, nuclei with unpaired protons or neutrons—which act like tiny magnets—align themselves with the field. This strong field causes these nuclei to undergo Larmor precession, tracing out a cone-shaped path at a specific natural frequency.123

The Role of Radio Waves

To probe the sample, a weak, oscillating radio wave field is applied. When the frequency of these radio waves matches the natural precession frequency of the nuclei, the system reaches resonance. At this point, the nuclei absorb energy from the radio waves and "flip" into a higher-energy orientation.132

Because nuclei in different chemical environments within a molecule require different, discrete frequencies to flip, scientists can correlate these absorbed frequencies to identify specific structural groups and atoms present in the material.42