Qualitative Analyses and Structural Determination by Mid-IR Absorption Spectroscopy

Qualitative Analyses and Structural Determination by Mid-IR Absorption Spectroscopy 

The value to qualitative analysis of prior knowledge about the sample cannot be overemphasized. Before trying to interpret an IR spectrum, it is important to find out as much as possible about the sample, For example, to identify the products of an organic reaction, it is very valuable to have information about the materials that were present before the reaction started, the compounds the reaction was expected to produce, the possible degradation products that may come about after the reaction, and so on. Armed with as much of this information as possible, we may be able to identify the molecules in the sample from their IR spectra. 

The region 1300-910 cm is called the fingerprint region because the complex absorption patterns are really what make the IR spectrum unique—a molecular fingerprint . These absorptions are not easily interpreted because they arise from interactions between vibrations. There are some very important bands in this region, especially the 

C—C—O band of alcohols and the C—O—C band of esters. These should be confirmed in conjunction with the appropriate bands (OH or C=0) in the functional group region of the spectrum. 

00 A at the bottom of the y-axis, resulting in the peaks pointing up to the top of the plot. This is the inverse of the traditional %T spectmm. One reason for this is that Raman spectra are plotted with peak intensity increasing from bottom to top of the plot having the complementary IR spectmm in the same format may make comparisons 

Before trying to interpret an IR spectrum, there are some things the analyst should note. The method of collecting the spectrum should be stated—mull, thin film, KBr pellet, solution, and the solvent—because the appearance of the spectrum may change as has been discussed earlier. The 

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