Structural Analysis of Organic Molecules

Infrared and Raman Spectroscopy

Overview

Infrared (IR) and Raman spectroscopy are essential techniques for analyzing molecular structures through vibrational modes. Visualizing these modes greatly facilitates spectral interpretation.

Fundamental Vibrational Modes

Symmetrical Stretching (ν_s)

Asymmetrical Stretching (ν_as)

Bending (Scissoring / Rocking)

Out-of-plane Bending (Wagging / Twisting)

Example: Acetone

C=O Symmetrical Stretching

Normal Modes of CH₂Cl₂

Symmetrical Stretching

Asymmetrical Stretching

Scissoring

Rocking

Wagging

Twisting

Simple Molecules

HCl: Stretching

H₂O: Symmetrical Stretching

H₂O: Asymmetrical Stretching

H₂O: Bending

N₂: Symmetrical Stretching

CO₂: Symmetrical Stretching

CO₂: Asymmetrical Stretching

CO₂: Bending (Mode 1)

CO₂: Bending (Mode 2)