Infrared spectroscopy is one of the most useful tools at the disposal of the inorganic chemist. While the theory of the absorption of infrared radiation is well understood, the degree of difficulty in predicting the complete vibrational spectra is usually prohibitive for complex molecules. Fortunately, it is found empirically that certain functional groups give rise to characteristic absorptions in narrow frequency ranges. These frequencies are tabulated in Group Frequency tables. However, caution must be exercised when using these tables. Assignments of bands should be in conjunction with additional chemical data to avoid error, i.e., quite different functional groups can give absorptions in the same region. Perhaps the most common error is the tendency to assign too many of the peaks found. The "fingerprint" region from 1400-700 cm-1 often contains a wealth of bands, many that result from complicated
bending and deformation modes of vibration - assignment of such bands is difficult and, most often, a fruitless task.
Infrared spectroscopy is one of the most useful tools at the disposal of the inorganic chemist. While the theory of the absorption of infrared radiation is well understood, the degree of difficulty in predicting the complete vibrational spectra is usually prohibitive for complex molecules. Fortunately, it is found empirically that certain functional groups give rise to characteristic absorptions in narrow frequency ranges. These frequencies are tabulated in Group Frequency tables. However, caution must be exercised when using these tables. Assignments of bands should be in conjunction with additional chemical data to avoid error, i.e., quite different functional groups can give absorptions in the same region. Perhaps the most common error is the tendency to assign too many of the peaks found. The "fingerprint" region from 1400-700 cm-1 often contains a wealth of bands, many that result from complicatedbending and deformation modes of vibration - assignment of such bands is difficult and, most often, a fruitless task.
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