IR Spectroscopy

Principle, table,  use

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IR spectroscopy involves the interaction of infrared radiation with matter and is used to determine the structure of both organic and inorganic substances.

It is also known as vibrational spectroscopy and it is based on the absorption of spectroscopy and determines the functional group.

Infrared radiation in the range from about 10000 cm−1 to 100 cm−1 is absorbed and converted by an organic molecule into the energy of molecular vibration.

IR spectroscopy is important spectroscopy that gives sufficient information about the structure of a compound.

This technique can be used to identify the given compound by comparing spectra with known compounds.

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Principle of IR spectroscopy

When IR radiation is absorbed by the molecules, excitation of molecules from a lower to a higher vibrational level occurs.

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All bonds in a molecule are not capable of absorbing infra-red energy but only those bonds which are accompanied by a change in dipole moment will be absorbed in the infra-red region.

Since each vibrational energy level is quantized, only a definite wave number of IR light is absorbed by the molecules.   Each bond will absorb a characteristic frequency or wave number which allows us to determine the functional group.

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When IR light is passed through compounds, the energy is absorbed by bonds and undergoes various types of vibration.

1. Stretching 2. Bending

The various stretching and bending vibrations of a bond occur at a certain quantized level and the bending vibrational occurs at a lower wavenumber than the stretching vibration because the bending vibration requires lesser energy.

Fingerprint and functional group region

The region ranging from 4000 cm-1 to 1300 cm-1, the high-frequency region, is called the functional group region. Similarly, the region of the spectrum ranging from 1300 cm-1 to 900 cm-1 is called the fingerprint region.

Application of Infrared spectroscopy

Infrared spectroscopy can be used in both qualitative and quantitative analysis.

1. Determines the functional groups 2. Determination of  the molecular weight of polymers. 3. Used in determining the purity of the sample, and so on

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