Page 75 - Practical-organic-3
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✓ Infrared spectroscopy or vibrational spectroscopy is concerned with the study of absorption of
infrared radiation which results in vibrational transitions.
✓ Every bond or part of a molecule or functional group requires different frequency for
absorption.
✓ Absorption of IR light causes excitation of the vibrational motions available of a molecule.
These include bond stretching vibrations and bond bending vibrations.
✓ The vibrational modes of a molecule are quantized, so they occur only at specific
frequencies which correspond to the frequency of IR light.
▪ Modes of molecular vibration:
A. Stretching
• Symmetric.
• Asymmetric.
B. Bending
• In-plane bending: Scissoring & Rocking.
• Out-of-plane bending: Wagging & Twisting.
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