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What information can a spectrum provide about a molecule’s structure?

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Learn about the use of gamma-ray spectroscopy to identify the quarry that was the source of granite found in ancient Roman ruins — spectroscopy See how gamma-ray spectroscopy is used to identify the quarry that was the source of granite found in ancient Roman ruins.

Spectroscopy is an essential instrumental process for determining molecular structure by analyzing how molecules interact with electromagnetic radiation through absorption, emission, or scattering. Because molecular energy levels are quantized, measuring the specific wavelengths of radiation absorbed or emitted allows chemists to correlate these values with structural details.12

Different spectroscopic techniques provide distinct types of structural information:

Infrared (IR) Spectroscopy: By measuring vibrational motions—such as bond stretching and bending—IR spectra reveal the presence of specific functional groups. Because these vibrations are unique to specific molecular entities, the resulting spectrum acts as a "fingerprint" for identification.34
Nuclear Magnetic Resonance (NMR) Spectroscopy: This technique provides the most detailed structural information by measuring the magnetic environment of atomic nuclei, particularly hydrogen and carbon-13, within a molecule.5
Visible and Ultraviolet (UV) Spectroscopy: These methods help characterize electron distributions and are particularly useful for identifying chromophores or conjugated systems.6
Mass Spectrometry: While not dependent on electromagnetic radiation, this technique identifies the number and type of atoms present by measuring the mass and abundance of molecular fragments, helping to establish the molecular formula.17

Together, these techniques allow scientists to decipher the architecture of complex molecules.7