IR

IR Absorbances of Common Functional Groups

The infrared spectrum of benzyl alcohol displays a broad, hydrogen-bonded -OH stretching band in the region 3400 cm^-1, a sharp unsaturated (sp²) CH stretch at about 3010 cm^-1 and a saturated (sp³) CH stretch at about 2900 cm^-1; these bands are typical for alcohols and for aromatic compounds containing some saturated carbon. Acetylene (ethyne) displays a typical terminal alkyne C-H stretch, as shown in the second panel.

Saturated and unsaturated CH bands also are shown clearly in the spectrum of vinyl acetate (ethenyl ethanoate). This compound also shows a typical ester carbonyl at 1700 cm^-1 and a nice example of a carbon-carbon double bond stretch at about 1500 cm^-1. Both of these bands are shifted to slightly lower wave numbers than are typically observed (by about 50 cm^-1) by conjugation involving the vinyl ester group.