Page 77 - Practical-organic-3
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Important note:
Not all covalent bonds are capable of absorbing IR energy or display bands in the IR spectrum.
Only polar bonds, that have a change in dipole moment, are capable to absorb IR radiation.
These are referred to as IR active. The intensity of the bands depends on the magnitude of
the dipole moment associated with the bond, where the larger the dipole change, the stronger
the intensity of the band in an IR spectrum:
• Strongly polar bonds such as carbonyl groups (C=O) produce strong bands.
• Medium polarity bonds and asymmetric bonds produce medium bands.
• Weakly polar bond and symmetric bonds produce weak or non-observable bands.
• Compounds do not absorb in IR region: O2, H2, N2, Cl2.
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