Infrared spectrum means that molecules can selectively absorb infrared rays with a certain wavelength, causing the transition of vibration energy level and rotation energy level in molecules. The infrared absorption spectrum of a substance can be obtained by detecting the absorption of infrared rays, which is also called molecular vibration spectrum or vibration rotation spectrum.
In organic molecules, atoms that make up chemical bonds or functional groups are in a state of constant vibration, and their vibration frequency is equivalent to that of infrared light. Therefore, when organic molecules are irradiated with infrared light, chemical bonds or functional groups in the molecules can be absorbed by vibration.
Different chemical bonds or functional groups have different absorption frequencies and will be in different positions in the infrared spectrum, so that the information of which chemical bonds or functional groups are contained in the molecule can be obtained.
This technique is specially used for valence bond analysis. If the sample has few infrared active bonds and high purity, the obtained spectrum will be quite clear and the effect will be very good. More complex molecular structure will lead to more bond absorption, thus obtaining complex spectra. However, this technique is still used for the qualitative study of very complex mixtures.
Advantages of infrared spectrum
1, fast: infrared spectroscopy can quickly analyze samples, especially for some automatic sample preparation and analysis, which can greatly improve the analysis efficiency.
2. No sample pretreatment: Compared with other analytical methods such as chromatography and nuclear magnetic resonance, infrared spectroscopy usually does not need complicated sample pretreatment, which saves time and effort.
3. Multifunctional: Infrared spectrum can be used for both qualitative analysis and quantitative analysis, and can also infer the structural information of compounds.
4. Wide application: infrared spectroscopy can be applied to many fields, such as material science, chemistry, biology and so on. This is a very general analysis method.