Ultraviolet-visible UV-Vis spectroscopy is a widely used analytical technique that involves the study of the absorption of ultraviolet and visible light by molecules. It can be used to identify the presence of specific functional groups in a given compound by analyzing the characteristic wavelengths or absorption bands associated with these functional groups.When a molecule absorbs light in the UV-Vis region, it undergoes electronic transitions, promoting electrons from lower energy levels ground state to higher energy levels excited state . Different functional groups in a molecule have distinct energy levels and electronic transitions, resulting in unique absorption patterns.To identify the presence of specific functional groups using UV-Vis spectroscopy, one can follow these steps:1. Prepare a sample solution of the compound in a suitable solvent.2. Record the UV-Vis spectrum of the sample solution using a UV-Vis spectrophotometer.3. Analyze the spectrum for characteristic absorption bands associated with specific functional groups.4. Compare the observed absorption bands with known reference data or literature values to confirm the presence of the functional groups.Here are some common functional groups and their characteristic absorption bands in the UV-Vis region:1. Conjugated -systems: Compounds with conjugated double bonds, such as dienes, polyenes, and aromatic systems, typically absorb in the range of 200-400 nm. The more extended the conjugation, the longer the wavelength of absorption.2. Carbonyl groups C=O : Aldehydes, ketones, and carboxylic acids usually exhibit absorption bands in the range of 170-190 nm for the n* transition and 270-290 nm for the * transition.3. Nitro groups NO2 : Nitro-containing compounds show strong absorption bands in the range of 300-600 nm due to the charge-transfer transition between the nitro group and the rest of the molecule.4. Amino groups NH2 : Amines and amides exhibit absorption bands in the range of 190-230 nm for the n* transition and 280-300 nm for the * transition.5. Sulfur-containing groups: Thiols, sulfides, and disulfides show absorption bands in the range of 250-300 nm due to the n* transition.It is important to note that the exact position of the absorption bands may vary depending on the molecular environment and the presence of other functional groups in the molecule. Additionally, UV-Vis spectroscopy is often used in conjunction with other analytical techniques, such as infrared IR spectroscopy and nuclear magnetic resonance NMR spectroscopy, to provide a more comprehensive understanding of the molecular structure and functional groups present in a compound.