Spectroscopic techniques are powerful tools used by chemists to identify the functional groups present in organic compounds. These techniques involve the interaction of electromagnetic radiation with matter, providing information about the structure and properties of molecules. Some common spectroscopic techniques used to identify functional groups in organic compounds include infrared IR spectroscopy, nuclear magnetic resonance NMR spectroscopy, and ultraviolet-visible UV-Vis spectroscopy.1. Infrared IR Spectroscopy: Infrared spectroscopy measures the absorption of infrared radiation by a molecule as a function of its frequency or wavelength. Different functional groups have characteristic absorption bands in the IR region due to their specific vibrational modes. By analyzing the absorption spectrum, one can identify the functional groups present in the compound. For example, carbonyl groups C=O typically show a strong absorption band around 1700 cm-1, while hydroxyl groups O-H have a broad absorption band around 3200-3600 cm-1.2. Nuclear Magnetic Resonance NMR Spectroscopy: NMR spectroscopy is based on the interaction of nuclear spins with an external magnetic field. It provides information about the chemical environment of specific nuclei mainly 1H and 13C in a molecule. By analyzing the chemical shifts, coupling constants, and splitting patterns in the NMR spectrum, one can deduce the functional groups and their connectivity in the compound. For example, an aldehyde group R-CHO typically shows a 1H NMR signal around 9-10 ppm for the aldehydic proton, and a 13C NMR signal around 190-200 ppm for the carbonyl carbon.3. Ultraviolet-Visible UV-Vis Spectroscopy: UV-Vis spectroscopy measures the absorption of ultraviolet or visible light by a molecule as a function of its wavelength. It is particularly useful for identifying chromophores or conjugated systems in organic compounds. The presence of specific functional groups can be inferred from the absorption maxima max and molar absorptivity values in the UV-Vis spectrum. For example, an ,-unsaturated carbonyl compound R-CH=CH-C=O typically shows an absorption band around 200-300 nm due to the -* transition in the conjugated system.Example: Suppose we have an unknown organic compound and want to determine its functional groups using spectroscopic techniques.1. IR Spectrum: We observe a strong absorption band around 1710 cm-1 and a broad absorption band around 3300 cm-1. This suggests the presence of a carbonyl group C=O and a hydroxyl group O-H in the compound.2. 1H NMR Spectrum: We observe a singlet signal around 9.8 ppm, indicating the presence of an aldehydic proton R-CHO . This is consistent with the carbonyl group observed in the IR spectrum.3. 13C NMR Spectrum: We observe a signal around 195 ppm, which corresponds to the carbonyl carbon of an aldehyde group R-CHO .Based on the combined information from the IR, 1H NMR, and 13C NMR spectra, we can conclude that the unknown compound contains an aldehyde functional group R-CHO and a hydroxyl group O-H .