13.11 : תחום התדירות ב-IR: אזור טביעת אצבע

The IR spectrum can be divided into two main regions: The diagnostic region and the fingerprint region.

Bands in the diagnostic region arise from stretching absorptions of the bonds connected to hydrogen, and different types of triple bonds and double bonds.

The fingerprint region is the complex region in the IR spectrum between 1500 and 450 cm⁻¹, showcasing a large number of absorptions resulting from stretching and bending vibrations of various single bonds.

Each compound has a unique pattern of peaks in the fingerprint region which is useful for distinguishing molecules that have identical functional groups.

For instance, 2–butanol and 2–propanol exhibit identical C–H and O–H signals in the diagnostic region and are, therefore, indistinguishable. However, they have a different pattern of peaks in the fingerprint region, making them easily distinguishable.