What does spectroscopy tell us?

1 Answer
Jan 14, 2017

It gives us information about the identity and structure of a substance, or the substances present in a mixture and (sometimes) their quantities.


You asked this question under the category of infrared spectroscopy. Infrared spectroscopy gives us information about the bonds present in a substance. Molecules absorb infrared energy at different frequencies, making the bonds in the molecule vibrate. Each frequency corresponds to a specific vibrational mode of the molecule, and is influenced by the strength of the bond and the masses of the bonded atoms or groups. As a result, certain functional groups produce peaks in the infrared spectrum at characteristic frequencies.

For example, the presence of a sharp peak between #1680cm^-1# and #1750cm^-1# would suggest the presence of a carbonyl C=O group in the compound.

The size of the absorptions is related to the amount of the substance present in the sample, so it is possible to make a calibration curve and use infrared spectroscopy to monitor the progress of a reaction, or for quality control.