Infrared spectrum fingerprint region

Fingerprint region (Section 13 20) The region 1400-625 cm of an infrared spectrum This region is less character istic of functional groups than others but varies so much from one molecule to another that it can be used to deter mine whether two substances are identical or not Fischer esterification (Sections 15 8 and 19 14) Acid cat alyzed ester formation between an alcohol and a carboxylic acid... 

Figure 12.15 The four regions of the infrared spectrum single bonds to hydrogen, triple bonds, double bonds, and fingerprint.

Fingerprint region (Section 12.7) The complex region of the infrared spectrum from 1500 to 400 cm-1. 

The next most useful is vibrational spectroscopy but identification of large molecules is still uncertain. In the laboratory, vibrational spectroscopy in the infrared (IR) is used routinely to identify the functional groups in organic molecules but although this is important information it is not sufficient to identify the molecule. Even in the fingerprint region where the low wavenumber floppy vibrational modes of big molecules are observed, this is hardly diagnostic of structure. On occasion, however, when the vibrational transition can be resolved rotationally then the analysis of the spectrum becomes more certain. 

The fingerprint region lies between 1300-400 cm-1 which is considered to be the most valuable component of the spectra and mainly comprises of a specifically large number of unassigned vibrations. Therefore, IR-spectroscopy aids in the identification of unknown compound by comparing its spectrum with a standard spectra recorded under exactly similar experimental parameters. Thus, pharmaceutical substances that exhibit the same infrared spectra may be inferred as identical. 

FIGURE 2.6 Infrared absorption spectrum obtained in the fingerprint region for clopidogrel bisulfate, Form-I. 

Know the meaning of the functional group region and fingerprint region of an infrared spectrum, and tell what kind of information can be obtained from each. 

Figure 8. Fingerprint region of the attenuated total reflectance infrared spectrum of etodolac.

Fingerprint region (Section 13.9) The region below 1500 cm-1 in the infrared spectrum that contains numerous absorptions due to single bond stretches and a variety of bending vibrations. Because of the large number of bands, this is the region where comparison of the spectrum of an unknown to that of a known compound can establish the identity of the unknown. 

It is highly unlikely that the IR spectra of two different compounds (except enantiomers) will show the same frequencies for all their various complex vibrations. For this reason, the infrared spectrum provides a fingerprint of a molecule. In fact, the region of the IR spectrum containing most of these complex vibrations (600 to 1400 cm-1) is commonly called the fingerprint region of the spectrum. 

Infrared spectroscopy can provide conclusive proof that two compounds are either the same or different. The peaks in the fingerprint region depend on complex vibrations involving the entire molecule, and it is highly improbable for any two compounds (except enantiomers) to have precisely the same infrared spectrum. 

Infrared spectroscopy can be applied to V. the characterization of polymeric materials at various levels of sophistication. As most commonly used, it is a rapid and easy method for the qualitative identification of major components through the use of group frequencies and distinctive patterns in the fingerprint region of the spectrum. Let s look at a couple of examples. 

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