Carbonyl group infrared absorption bands

Table 13.1 Infrared Absorption Band Positions ofVarious Carbonyl Groups...

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. 

The carbonyl group (C=0) gives infrared absorption bands in 1750-1735 cm . The C—H stretching vibrations produce bands in 1300-1180 cm . Aliphatic and aromatic esters may conveniently be analyzed by GC nsing flame ionization detector. A column snch as 10% SP-1000 or 5% FLAP on Chro-mosorb W-HP is suitable for the purpose. 

Esters are usually readily identified by their spectroscopic properties (70). Among these, infrared spectroscopy (ir) is especially useful for identifying the carbonyl of the ester group that has characteristic absorption bands. The C=0 absorption is very strong in the ir at 1750-1735 cm in addition,... 

Except in simple cases, it is very difficult to predict the infrared absorption spectrum of a polyatomic molecule, because each of the modes has its characteristic absorption frequency rather than just the single frequency of a diatomic molecule. However, certain groups, such as a benzene ring or a carbonyl group, have characteristic frequencies, and their presence can often be detected in a spectrum. Thus, an infrared spectrum can be used to identify the species present in a sample by looking for the characteristic absorption bands associated with various groups. An example and its analysis is shown in Fig. 3. 

Fourier transform infrared spectroscopy (FTIR) was also used to study the anisotropic structure of polyimide films. This work was based on the fact that there are characteristic absorptions associated with in-plane and out-of-plane vibrations of some functional groups, such as the carbonyl doublet absorption bands at 1700-1800 cm . The origin of this doublet has been attributed to the in-phase (symmetrical stretching) and out-of-phase (asymmetrical stretching) coupled... 

Morrissey 53) used transmission infrared spectroscopy to study protein adsorption onto silica particles in a heavy water (DzO) buffer. By observing the shift in the amide I absorption band, he could deduce the fraction of protein carbonyl groups involved in bonding to the silica surface. He found that bovine IgG had a bound fraction of 0.20 at low bulk solution concentrations, but only about 0.02 at high solution concentrations. However, neither prothrombin nor bovine serum albumin exhibited a change in bound fraction with concentration. Parallel experiments with flat silica plates using ellipsometry showed that the IgG-adsorbed layers had an optical thickness of 140 A and a surface concentration of 1.7 mg/m2 at low bulk solution concentration — in concentrated solutions the surface amount was 3.4 mg/m2 with a thickness of 320 A (Fig. 17). 

The infrared spectra of a-amino acids in the solid state or in solution do not show a carbonyl absorption band at 1720 cm"1 characteristic of a carboxyl group. Rather, they show a strong absorption near 1600 cm"1 typical of the carboxylate anion. The N—H stretch appears as a strong, broad band between 3100-2600 cm"1 ... 

Infrared spectral studies on molybdenum hexacarbonyl-alumina were reported by Davie, Whan, and Kemball 78). Without any activation procedure they obtained a sharp carbonyl frequency corresponding to unchanged hexacarbon-yl on the support. This material was not active for disproportionation. After treatment for one hour under vacuum at 373 °K the catalyst had lost the sharp carbonyl band but showed two wider and broader bands and was active for dis-proportionating propylene. The authors stated that the active catalyst clearly had a lower symmetry than the hexacarbonyl and must have lost one or more of the carbonyl groups. After exposure of the activated catalyst to air, the catalyst was inactive and showed no absorption in the carbonyl region. 

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