This title slide introduces "Infrared (IR) Spectroscopy." It is presented by the Department of Applied Chemistry at Yeshwantrao Chavan College of Engineering for the 2025-26 academic year.

Infrared (IR) Spectroscopy

Yeshwantrao Chavan College of Engineering – Department of Applied Chemistry (2025-26)

Source: Yeshwantrao Chavan College of Engineering – Department of Applied Chemistry (2025-26)

IR Spectroscopy is an analytical technique that measures the absorption of infrared light by molecules, exciting their vibrations. It produces a characteristic absorption spectrum for identifying molecular functional groups.

Introduction to IR Spectroscopy

• Analytical technique measuring absorption of infrared light by molecules.
• IR radiation excites molecular vibrations.
• Produces characteristic absorption spectrum.
• Enables identification of molecular functional groups.

Source: Yeshwantrao Chavan College of Engineering – Department of Applied Chemistry (2025-26)

The IR spectrum slide divides into the Functional Group Region (4000–1500 cm⁻¹), which shows characteristic absorptions for groups like O-H, C=O, and C-H to detect their presence, and the Fingerprint Region (1500–400 cm⁻¹), featuring a unique pattern of peaks for molecule identification. These regions enable functional group confirmation and compound comparison via spectral matching.

Regions of the IR Spectrum

Infrared spectroscopy relies on molecular vibrations at specific frequencies, where IR absorption occurs only if the dipole moment changes during stretching (bond length changes) or bending (scissoring, rocking, wagging altering angles). The key principle is a frequency match between IR light and these molecular vibrations.

Principle of Infrared Spectroscopy

• Vibrational Theory: Molecules vibrate at specific frequencies.
• IR Absorption: Occurs if dipole moment changes during vibration.
• Stretching Modes: Change in bond length interacts with IR.
• Bending Modes: Scissoring, rocking, wagging alter bond angles.
• Key Takeaway: Frequency match between IR light and vibration.

Source: Department of Applied Chemistry, Yeshwantrao Chavan College of Engineering (2025-26)

The slide features a diagram of fundamental vibrations, highlighting symmetric and asymmetric stretching vibrations. It also illustrates bending modes such as scissoring, wagging, twisting, and rocking.

Fundamental Vibrations Diagram

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• Symmetric and asymmetric stretching vibrations.
• Bending modes: scissoring, wagging, twisting, rocking.

Source: Molecular vibration - Wikipedia

This slide features an IR correlation chart mapping functional groups to their characteristic wavenumber ranges in cm⁻¹. It lists O-H stretch (3200-3600), C-H stretch (2800-3300), C=O stretch (1650-1750), and C-O stretch (1000-1300).

Applications & IR Correlation Chart