Functional groups infrared absorptions

Infrared spectroscopy is an extremely useful tool for detecting the presence and type of functional group. Strong absorption bands are characteristic of various classes of monosaccharides containing a carbonyl group. 

Table 10.1 Correlation Chart in the mid-infrared between functional groups and absorption bands 4000 3500 3000 2500 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700...

An infrared spectrum can be divided into two areas. The area on the left (4(XX)—1400 cm ) is where most of the functional groups show absorption bands. This is called the fimctional group region. 

Infrared spectroscopy identifies functional groups. IR absorptions are reported in wavenumbers ... 

Polyatomic molecules vibrate in a very complicated way, but, expressed in temis of their normal coordinates, atoms or groups of atoms vibrate sinusoidally in phase, with the same frequency. Each mode of motion functions as an independent hamionic oscillator and, provided certain selection rules are satisfied, contributes a band to the vibrational spectr um. There will be at least as many bands as there are degrees of freedom, but the frequencies of the normal coordinates will dominate the vibrational spectrum for simple molecules. An example is water, which has a pair of infrared absorption maxima centered at about 3780 cm and a single peak at about 1580 cm (nist webbook). 

The two most useful supplementary techniques for the light microscope are EDS and FTIR microscopy. Energy dispersed x-ray systems (EDS) and Eourier-transform infrared absorption (ETIR) are used by chemical microscopists for elemental analyses (EDS) of inorganic compounds and for organic function group analyses (ETIR) of organic compounds. Insofar as they are able to characterize a tiny sample microscopically by PLM, EDS and ETIR ensure rapid and dependable identification when appHed by a trained chemical microscopist. 

As indicated above, the penetration depth is on the order of a micrometer. That means that in ATR, absorption of infrared radiation mostly occurs within a distance 8 of the surface and ATR is not as surface sensitive as some other surface analysis techniques. However, ATR, like all forms of infrared spectroscopy, is very sensitive to functional groups and is a powerful technique for characterizing the surface regions of polymers. 

Infrared absorption spectra of heteropyrans have been used mainly for the identification of functional groups. Assignments of the bands belonging to heterocyclic bond vibrations (C=C, C—S, C—Se, C—Te) have not been common. As a rule, 4W-heteropyrans exhibit maxima at higher wave numbers than 2//-isomers. Typical IR absorption maxima for heteropyrans are shown in Table X. 

Fan, L., Ziegler, T., 1992, Application of Density Functional Theory to Infrared Absorption Intensity Calculations on Main Group Molecules , J. Chem. Phys., 96, 9005. 

Analysis of infrared spectra, in which molecules that share structural features, such as a common functional group, give rise to spectra with spectral similarities. ANNs can be used to link spectral features, such as strong absorption at a particular energy, with molecular structure and, thus, help in the interpretation of spectra. 

We have already met one tool that can be used to investigate the links that exist among data items. When the features of a pattern, such as the infrared absorption spectrum of a sample, and information about the class to which it belongs, such as the presence in the molecule of a particular functional group, are known, feedforward neural networks can create a computational model that allows the class to be predicted from the spectrum. These networks might be effective tools to predict suitable protective glove material from a knowledge of molecular structure, but they cannot be used if the classes to which samples in the database are unknown because, in that case, a conventional neural network cannot be trained. 

Functional groups in the substituent at the carbon atom can take part in the formation of new tautomeric forms, as in 115, [Eq. (92)] (87IZV2118 89IZV946 90IZV1133). Infrared spectra of 121 in solvent contain absorption bands for the hydroxyl groups and the N+—H fragment, the former... 

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