Infrared IR spectroscopy is a powerful analytical technique that allows us to identify the functional groups present in an unknown compound and determine its chemical structure. It works by measuring the absorption of infrared radiation by the molecules in a sample, which causes the vibrational transitions of the chemical bonds within the molecule. Different functional groups have characteristic absorption bands in the infrared region, which can be used as a fingerprint to identify them.Here's a step-by-step guide on how to use infrared spectroscopy to identify functional groups and determine the chemical structure of an unknown compound:1. Obtain the IR spectrum of the unknown compound: First, prepare a suitable sample of the compound, either as a thin film, a mull, or a KBr pellet. Then, record the IR spectrum using an infrared spectrometer. The resulting spectrum will display the absorbance or transmittance of the sample as a function of wavenumber cm .2. Identify the characteristic absorption bands: Examine the IR spectrum and look for the characteristic absorption bands associated with different functional groups. These bands are usually found in specific wavenumber regions, such as: - O-H stretch: 3600-3200 cm alcohols, carboxylic acids - N-H stretch: 3500-3300 cm amines, amides - C-H stretch: 3100-2800 cm alkanes, alkenes, alkynes, aromatics - C=O stretch: 1850-1650 cm ketones, aldehydes, carboxylic acids, esters, amides - C=C stretch: 1680-1620 cm alkenes, aromatics - CC and CN stretch: 2260-2100 cm alkynes, nitriles - C-N stretch: 1350-1000 cm amines, amides, nitro compounds 3. Analyze the fingerprint region: The fingerprint region 1500-500 cm contains many absorption bands that are specific to individual compounds. Comparing the fingerprint region of the unknown compound with those of known compounds can help confirm the presence of certain functional groups and provide additional information about the chemical structure.4. Combine the information from the absorption bands: Once you have identified the characteristic absorption bands and analyzed the fingerprint region, combine this information to deduce the functional groups present in the unknown compound. This will help you determine its chemical structure.5. Confirm the structure using other analytical techniques: Infrared spectroscopy is a valuable tool for identifying functional groups and determining chemical structures, but it is often necessary to use additional analytical techniques, such as nuclear magnetic resonance NMR spectroscopy or mass spectrometry, to confirm the structure of the unknown compound.By following these steps, you can use infrared spectroscopy to identify the functional groups present in an unknown compound and determine its chemical structure.