BRAINCAKEInfrared Spectroscopy
Infrared (IR) spectroscopy is an analytical technique used to identify the bonds, and so the functional groups, present in an organic molecule.
A beam of infrared radiation covering a range of frequencies is passed through a sample. Covalent bonds absorb IR radiation at particular frequencies. A detector measures how much radiation passes through at each frequency, and a computer plots the IR spectrum.
An IR spectrum plots percentage transmittance (vertical axis) against wavenumber (horizontal axis). Wavenumber is 1 ÷ wavelength, measured in cm−1, and is proportional to frequency: a higher wavenumber means higher-frequency, higher-energy radiation. Spectra usually run from 4000 cm−1 on the left down to about 500 cm−1 on the right.
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Key terms in this lesson
- functional group
- A group of atoms in a molecule responsible for its characteristic chemical reactions.
More in Analytical Techniques
- Bond Vibrations and IR Absorption
- Characteristic IR Absorptions
- Interpreting IR Spectra
- IR in Breathalysers and Pollution Monitoring
- Mass Spectrometry of Organic Compounds
- The Molecular Ion Peak
- The M+1 Peak
- Fragmentation
All 10 lessons in Analytical Techniques · All OCR AS-level Chemistry topics