Fingerprint regions

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... 

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

A further aid to identification comes from the fact that a molecule commonly has complex series of absorptions spanning a range of wavelengths. This fingerprint region of the spectrum may be too difficult to analyze in detail, but its presence enables us to recognize the substance by comparing the spectrum to an atlas of spectra. 

Figure 3. Fingerprint region of the COSY spectrum of RpII in H O showing the amide to a proton connectivities. Cross peaks are labeled with the identity of the amino acid in the sequence from which they arise.

Techniques for differentiating between amorphous and crystalline are (i) sharp melting point, (ii) sharp peaks in the solid state infrared fingerprint region, (iii) optical birefringence observed when solid is viewed in a phase contrast microscope and (iv) sharp peaks in the powder X-ray diffraction pattern. 

Because much smaller differences are anticipated at the strain level, strain-level differentiation and spectral reproducibility have received much attention. A 1998 work from Riley s group21 is representative of a common approach to this issue. In Riley s studies E. coli strains shared many peaks in common but also showed strain-unique ions as well. Many of these ions fell in the fingerprint region near 3630, 3850, 4170, 4780, 5100, 5380, 7280, 8320,... 

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. 

In one application, Raman spectroscopy was used to identify and quantitate various drugs present in polymer matrices [21]. In Fig. 2, Raman spectra obtained within the fingerprint region for diclofenac, sodium alginate, and a 20% dispersion of diclofenac in sodium alginate are shown. It is evident in the spectra... 

Infrared spectroscopy is an excellent tool in iminoborane chemistry, which readily permits, to distinguish between iminoboranes and nitrile-borane adducts and to identify monomeric and dimeric forms of iminoboranes. This event is due to the fact that the i>CN of CN multiple bonds absorbs outside the fingerprint region and can be considered to be a valuable group frequency even when mixed with other vibrational modes. In some cases other vibrations like NH, BH, B-halogen or B-S stretching modes are helpful for determining the structure of iminoboranes. 

The fingerprint region (1500-500 cm 1), where all single bonds between carbon and elements such as nitrogen, oxygen, sulfur and halogens absorb... 

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