Infrared spectroscopy (IR) involves the interaction of infrared radiation with matter. Functional groups can behave (vibrate and stretch, flex or wiggle around) at various ranges of the spectrum based on kind of functional group. This is used to study and identify chemical compounds.

The width and location of the peak within an IR is a sign of the functional group is responsible for the peak. Alcohol and carboxylic acid peaks are very broad verses carbonyl peaks which are very narrow and sharp. The benzene rings that are substituted have peak that are in line with the pattern of substitution (Mono para, meta and so on) in the overtone and fingerprint region of IR.