(16) IR Spectroscopy | Introduction to Infrared (IR) Spectroscopy | Instrumental Method of Analysis

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Infrared (IR) spectroscopy is a technique used to analyze the molecular composition and structure of compounds based on their interaction with infrared radiation. This method is widely employed in chemistry, biochemistry, and materials science for identifying functional groups in molecules and elucidating their structures.
Principles of IR Spectroscopy:
Molecular Vibrations: Molecules consist of atoms held together by chemical bonds. When these bonds absorb infrared radiation, they undergo vibrational transitions, causing them to stretch, bend, or twist.
Infrared Radiation: The infrared region of the electromagnetic spectrum lies between visible light and microwaves. It includes wavelengths ranging from about 0.78 to 1000 micrometers.
Absorption Spectra: When IR radiation passes through a sample, certain wavelengths get absorbed by the molecules, leading to characteristic absorption patterns based on the vibrational modes of the bonds present in the molecule.
Key Components of IR Spectroscopy:
IR Source: Emits a broad spectrum of infrared radiation.
Sample Compartment: Where the sample is placed for analysis.
Detector: Measures the intensity of transmitted or absorbed IR radiation.
Interferometer: In Fourier-transform infrared (FTIR) spectroscopy, an interferometer is used to modulate the IR beam and capture the interferogram, which is converted into the IR spectrum.
Modes of Vibration:
1. Stretching Vibrations: Occur when the distance between two atoms increases or decreases along the bond axis.
2. Symmetrical Stretching (ν): Both atoms move away or toward the central atom simultaneously.
Asymmetrical Stretching (ν): One atom moves while the other remains stationary.
3. Bending Vibrations: Involve a change in the angle between two bonds, resulting in a bending motion.
Scissoring (δ): Movement resembling a pair of scissors.
Rocking (ρ): A rocking motion.
Wagging (ω): A pendulum-like motion.
Twisting (τ): Rotation about the bond axis.
Applications:
1. Compound Identification: IR spectra serve as fingerprints, aiding in the identification of functional groups and molecular structures in compounds.
2. Quality Control: Used in industries to assess the purity of substances and monitor chemical reactions.
3. Forensic Analysis: Helps in identifying unknown substances in forensic investigations.
4. Pharmaceuticals: Used to characterize drug compounds and ensure their purity.
5. Material Sciences: Determines the composition and properties of materials, including polymers and ceramics.
IR spectroscopy is a powerful analytical technique that provides valuable information about the molecular composition and structure of various compounds, making it an essential tool in research and industrial laboratories.
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