Question

Discuss absorption bands in IR spectroscopy with examples in one to two paragraphs.

Answer 1

When the light ( having frequencies in the IR region) is passed through a sample, acertain frequeinces are absorbed by the sample which gives absorption bands in IR spectroscopy. In the IR spectrum, a garph of absorbance (on y axis) vs frequency (or wavelength) on x axis is plotted. Instead of absorbacne, we can also plot transmittance on y axis.

Different functional groups absorb lights of different regions.
For example O-H stretch of alcohol is in the region 3200-3550 cm-1.
it is a strong, broad peak.
For alkyl cyanides, the -C \equiv N stretch is in the region 2210 - 2260 cm-1.

Thus by knowing the region in which the absorbption appears, we can predict which functional group is present.