Infrared Spectroscopy
A technique that identifies functional groups from the infrared frequencies a molecule absorbs as its bonds vibrate.
Formula / equation
ν̃ = (1/2πc)√(k/μ)
Unit
cm⁻¹
In depth
A bond absorbs infrared radiation only if the vibration changes the molecular dipole moment, which is why symmetric molecules such as N₂ are transparent. Absorption frequency rises with bond strength and falls with the reduced mass of the vibrating atoms.
Examples in the real world
A broad O–H band near 3300 cm⁻¹ for alcohols; a sharp C=O stretch near 1700 cm⁻¹ for carbonyls.