What does infrared spectrum show in an IR?

1 Answer
Jul 14, 2015


The infrared spectrum tells us what functional groups are present in a molecule.


The bonds in molecules are vibrating, and the vibrational energy is quantized.

The bonds can stretch and bend only at certain allowed frequencies.

A molecule will absorb energy from radiation that has the same energy as its vibrational modes.

This energy is in the infrared region of the electromagnetic spectrum.

Each functional group has vibrational frequencies in a small region of the IR spectrum, so IR spectra give us information about the functional groups that are present.

Here is a table that lists the characteristic vibrational frequencies of some functional groups.

Table 2
(from www.chromatographytechniques.com)