Fundamentals of Infrared Spectroscopy and Spectrum Analysis

Infrared Spectroscopy (IR) is an experimental technique which is widely used in the fields of chemistry, biology, and material science. The basic principle is that the chemical bonds in molecules absorb infrared radiation at certain frequencies, causing bond vibrations. The Infrared spectroscopy graph shows the specific frequencies at which a material absorbs infrared radiation.

 

Basic Steps and Key Points for Interpreting an Infrared Spectroscopy Graph

1. Identifying the Major Peaks

First, it identifies the major absorption peaks on the graph, which correspond to certain specific chemical bonds or functional groups.

 

2. Matching Known Frequencies

Using infrared spectroscopy handbooks or databases to match the observed absorption peaks with the known absorption frequencies of chemical bonds or functional groups.

 

3. Paying Attention to the Shape and Intensity of Peaks

In addition to frequency, the shape and intensity of the peaks are also important sources of information. For example, broad and weak peaks might be caused by hydroxyl (OH), while sharp, intense peaks might be due to carbon double bonds (C=C).

 

4. Considering Possible Functional Groups

Certain functional groups usually show absorption peaks within specific frequency ranges. For example, hydroxyl usually shows peaks between 3200-3600 cm⁻¹, and the C=O bond of a ketone shows peaks between 1700-1750 cm⁻¹.

 

5. Combining with Other Information

Infrared spectroscopy is often used in conjunction with other spectroscopy methods (such as nuclear magnetic resonance or mass spectroscopy) to obtain more comprehensive information about the structure of a compound.

 

6. Noting the Types of Molecular Vibrations

The basic types of vibrations include stretching vibrations, bending vibrations, and twisting vibrations. Different types of vibrations will produce absorption peaks in different frequency ranges.

 

7. Considering Possible Impurities or Solvent Peaks

During graph interpretation, possible impurities or solvents in the sample that might also produce absorption peaks on the graph should be taken into account.

 

Interpreting an infrared spectroscopy graph requires some experience and a deep understanding of chemical structures. For beginners, it's recommended to reference infrared spectroscopy handbooks or databases and combine data from other spectroscopy techniques.