Infrared Spectroscopy



The electromagnetic spectrum encompasses electromagnetic waves from gamma rays to radio waves. The waves with the highest frequency, smallest wavelength, and most energy are gamma rays. The waves with the lowest frequency, largest wavelength, and least energy are radio waves. Visible light is a very small section of the electromagnetic spectrum that humans can see with their eyes. The visible light range goes from violet to red light. Waves that have a longer wavelength and less energy than red light on the spectrum are infrared light. Infrared light interacts with organic compounds, causing the covalent bonds to vibrate, stretch, and bend. An infrared spectrometer will interpret the vibrating, stretching, and bending to determine the functional groups in an organic compound.

At A Glance

  • Light can behave as both a wave and a particle. The energy and frequency of light are directly related to each other but inversely related to the wavelength.
  • Infrared (IR) spectroscopy measures the interaction between organic molecules and infrared light and is used to determine the functional groups present in an organic compound.
  • When infrared (IR) light interacts with organic molecules, it is too weak to fragment the bonds but instead just makes them vibrate, which can translate to stretching or bending of the covalent bonds.
  • Infrared (IR) spectra tables show the common absorbances of different functional groups. Additionally, the shape and intensity of the stretch can give information about the functional group.
  • An infrared (IR) spectrometer works by shining IR light on a sample. In modern Fourier-transform infrared spectroscopy (FT-IR), all frequencies are scanned at once and either the light absorbed or the light transmitted is measured.
  • By using the infrared (IR) spectra data table and the IR spectrum of a compound, the functional groups in a molecule can be determined and compounds containing different functional groups can be distinguished from one another.