Group Frequencies
Detailed information about the infrared absorptions observed for various bonded atoms and groups is usually presented in tabular form. The following table provides a collection of such data for the most common functional groups. Following the color scheme of the chart, stretching absorptions are listed in the blue-shaded section and bending absorptions in the green shaded part. More detailed descriptions for certain groups (e.g. alkenes, arenes, alcohols, amines & carbonyl compounds) may be viewed by clicking on the functional class name. Since most organic compounds have C-H bonds, a useful rule is that absorption in the 2850 to 3000 cm^-1 is due to sp³ C-H stretching; whereas, absorption above 3000 cm^-1 is from sp² C-H stretching or sp C-H stretching if it is near 3300 cm^-1.

To illustrate the usefulness of infrared absorption spectra, examples for five C₄H₈O isomers are presented below their corresponding structural formulas. The five spectra may be examined in turn by clicking the "Toggle Spectra" button. Try to associate each spectrum (A - E) with one of the isomers in the row above it. When you have made assignments check your answers by clicking on the structure or name of each isomer.