Infrared IR spectroscopy is a powerful analytical technique used to identify and study chemical compounds based on their absorption of infrared radiation. When a molecule absorbs infrared radiation, it causes the bonds within the molecule to vibrate at specific frequencies. These frequencies are unique to the functional groups and types of bonds present in the molecule, allowing chemists to identify the molecular structure and functional groups of the compound.A specific example of how IR spectroscopy can be used to distinguish between two isomers is the differentiation between cis and trans isomers of 2-butene C4H8 . Cis-2-butene and trans-2-butene are geometric isomers that differ in the arrangement of their substituents around the carbon-carbon double bond.In the case of cis-2-butene, the two methyl groups CH3 are on the same side of the double bond, whereas in trans-2-butene, the two methyl groups are on opposite sides of the double bond. This difference in the arrangement of the substituents affects the vibrational frequencies of the molecules, which can be detected using IR spectroscopy.For example, the stretching frequency of the carbon-carbon double bond C=C in cis-2-butene is around 1645 cm, while in trans-2-butene, it is around 1670 cm. Additionally, the out-of-plane bending frequency of the hydrogen atoms H-C=C-H in cis-2-butene is around 725 cm, while in trans-2-butene, it is around 970 cm. By analyzing these differences in the IR spectra, chemists can distinguish between the cis and trans isomers of 2-butene.In summary, IR spectroscopy is a valuable tool for identifying compounds and distinguishing between isomers based on their unique vibrational frequencies. In the example provided, IR spectroscopy can be used to differentiate between cis-2-butene and trans-2-butene by analyzing the differences in their C=C stretching and H-C=C-H bending frequencies.