What To Look for When Examining Infrared Spectra

7 WHAT TO LOOK FOR WHEN EXAMINING INFRARED SPECTRA 

The strong absorption at 1715 cm that corresponds to the carbonyl group (C=0) is quite intense. In addition to the characteristic position of absorption, the shape and intensity of this peak are also unique to the C=0 bond. This is true for almost every type of absorption peak both shape and intensity characteristics can be described, and these characteristics often enable the chemist to distinguish the peak in potentially confusing situations. For instance, to some extent C=0 and C=C bonds absorb in the same region of the infrared spectrum  

However, the C=0 bond is a strong absorber, whereas the C=C bond generally absorbs only weakly (Fig. 2.5). Hence, trained observers would not interpret a strong peak at 1670 cm- to be a C=C double bond, nor would they interpret a weak absorption at this frequency to be due to a carbonyl group. 

FIGURE 2.4 The infrared spectrum of 3-methyl-2-butanone (neat liquid, KBr plates). 

The shape and fine structure of a peak often give clues to its identity, as well. Thus, although the N—H and 0—H regions overlap, 

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What to Look for When Examining Infrared Spectra... 

B. Fourier Transform Spectrometers 25 Preparation of Samples for Infrared Spectroscopy 26 What to Look for When Examining Infrared Spectra 26 Correlation Charts and Tables 28... 

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