Practice question

Infrared spectrum divides into functional group region above 1500 cm-1 and fingerprint region below. The fingerprint region, commonly cited as approximately 1200 to 700 cm-1 though sometimes extended to 1500-400 cm-1, contains dense pattern of single-bond stretches, in-plane and out-of-plane bending, and combination vibrations highly sensitive to molecular skeleton and substitution pattern. Even close structural isomers generate different fingerprints. Because absorption here is unique to overall molecular framework, comparison of this region with spectral libraries allows definitive identification of small metabolites and confirmation of protein side-chain modifications after functional groups assignment.