Group frequencies , near infrared

A further development in the characterization resulted from a study of the near infrared region, by Washburn and Mahoney who showed that the first overtone of the cyclopropyl C-H stretching frequency absorbs at 6097 cm with a combination band also present at ca. 4465 cm . The overtone band is sharp though weak and separated from the first overtone of the saturated aliphatics. Any possible ambiguity with terminal methylene groups can be removed in infrared spectroscopic terms by analysis of the fundamental of the methylene. 

The interpretation of infrared spectra requires practice, but the task is eased with the help of correlation charts of group frequencies [2, 3]. Such a chart is shown in Figure 8.10, pp. 118-19. Other charts are available that document group frequencies in the near infrared and the far infrared. 

Once an infrared spectrum has been recorded, the next stage of this experimental technique is interpretation. Fortunately, spectrum interpretation is simplified by the fact that the bands that appear can usually be assigned to particular parts of a molecule, producing what are known as group frequencies. The characteristic group frequencies observed in the mid-infrared region are discussed in this chapter. The types of molecular motions responsible for infrared bands in the near-infrared and far-infrared regions are also introduced. 

A similar behaviour, as the one from C PyBr, has already been reported for surfactants with a silane head-group adsorbed on smooth silicon surfaces, using FT-IR [34] or vibrational sum-frequency generation [35]. After observing the same relative band ratios for excitation in the visible and in the near infrared spectral range, it can be... 

Raman spectroscopy is a vibrational spectroscopic technique which can be a useful probe of protein structure, since both intensity and frequency of vibrational motions of the amino acid side chains or polypeptide backbone are sensitive to chemical changes and the microenvironment around the functional groups. Thus, it can monitor changes related to tertiary structure as well as secondary structure of proteins. An important advantage of this technique is its versatility in application to samples which may be in solution or solid, clear or turbid, in aqueous or organic solvent. Since the concentration of proteins typically found in food systems is high, the classical dispersive method based on visible laser Raman spectroscopy, as well as the newer technique known as Fourier-transform Raman spectroscopy which utilizes near-infrared excitation, are more suitable to study food proteins (Li-Chan et aL, 1994). In contrast the technique based on ultraviolet excitation, known as resonance Raman spectroscopy, is more commonly used to study dilute protein solutions. 

Infared Analysis. The molecule is 4-chlorobenzaldehyde.The infrared spectrum of this aromatic aldehyde (Fig. 6.18, page 182) is rich and interesting.The aromatic aldehyde macro group frequency train (see Strategies for Interpreting Infrared Spectra) consists of peaks near 3090, 3070, 2830 and 2750, 1706, 1602, 1589, and 1396 cm ... 

Characteristic group frequencies of alkenes are shown in Figure 11. In alkenes, the =CH stretching vibration generally occurs above 3000 cm". In symmetrical irans or symmetrical tetrasubstituted double-bond compounds, the C=C stretching frequency near 1640cm, usually a medium intensity band, is infrared inactive because, in this... 

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