Carbonyl vibrations, infrared

The initial observation is that PMMA is essentially completely degraded to monomer by heating to 375°C in a sealed tube while heating a mixture of red phosphorus and PMMA under identical conditions yields a solid, non-deqraded, product as well as a lower yield of monomer. One may observe, by 3C NMR spectroscopy, that the methoxy resonance is greatly decreased in intensity and methyl, methoxy phosphonium ions are observed by 31P NMR. Additional carbonyl resonances are also seen in the carbon spectrum, this correlates with a new carbonyl vibration near 1800 cm 1 in the infrared spectrum and may be assigned to the formation of anhydride. The formation of anhydride was also confirmed by assignment of mass spectra obtained by laser desorption Fourier transform mass spectroscopy, LD-FT-MS. 

The situation with 7V-acyloxy-/V-alkoxyureas and carbamates is similar although infrared data were mostly determined by liquid film or condensed phase (KBr/nujol mull).52,131 However, the limited data for V-acyloxy-TV-alkoxyureas (Table 2, entries 69-72) give amide carbonyl frequencies ca. 1730 cm-1 that are raised by some 37-40 cm-1 by acyloxylation. Values for carbamates (Table 2, entries 73-77) are higher (mostly 1780 cm-1) but are raised to a lesser extent (10-20 cm-1) relative to their parent carbamates. Clearly, carbonyl vibrational frequencies will be influenced strongly by the adjacent amino or alkoxyl group in both analogues. 

The infrared (IR) spectra recorded throughout irradiation show an increase in absorbance due to the formation of oxidized products. Because PS presents initial absorption bands in the carbonyl vibration region (1900-1500 cm-1), a subtraction of spectra has to be carried out in order to observe the shape of the carbonyl envelope due to the formation of the photoproducts (Figure 30.1). Several maxima or shoulders are observed in the carbonyl region at 1515, 1690, 1698, 1732 and 1785 cm-1. Another band with amaximumaround 1605 cm-1 isalsoobserved,even if the initial absorption of PS at 1603 cm-1 interfered in the subtraction. In the hydroxyl region, bands and shoulders at 3250,3450 and 3540 cm-1 are observed. 

Acetamido-5-deoxy-D-threo-pentulose and 5-acetamido-5-deoxy-L-erythro-pentulose (204) are obtainable by the bacterial oxidation of 1-acetamido-l-deoxy-D-arabinitol and 1-acetamido-l-deoxy-D-ribitol, respectively. Both ketoses are crystalline, and show a strong carbonyl vibration in their infrared spectra. Accordingly, they exist in the acyclic form. Their isopropylidene acetals are likewise acyclic. Furthermore, 5-acetamido-5,6-dideoxy-L-xylo-hexulose (205), obtainable by bacterial oxidation, shows a great tendency to assume the acyclic structure. 5-Acetamido-5-deoxy-L-xi/io-hexulose (206) may be obtained by the bacterial oxidation of 2-acetamido-2-deoxy-D-glucitol it assumes, exclusively, the sterically more-favored pyranose form. ... 

The most important infrared absorption of carboxylic acids and their derivatives is the result of the C=0 stretching vibration. Infrared spectroscopic data for these derivatives and the other carbonyl-containing compounds are summarized in Table 12.7. 

Ibillty of spectroscopic characterization [76]. In the orthopedics community infrared spectroscopy has been the chosen analytical tool for the quantification of oxidation. Figure 3 shows two Infrared spectra from UHMWPE, one unirradiated and the other highly oxidized. Note that in the highly oxidized sample there is absorbance in the wave number range of 1680-1800 cm wbicb is known to be due to carbonyl containing chemical species, such as ketones, esters, aldehydes, and acids [84]. Calculating the area under the vibrational peak can provide quantification of the carbonyl vibration. This value is normalized to obtain a dimensionless number. 

An infrared (IR) spectrum of MA is shown in Fig. 1-5. The most characteristic anhydride bands appear at -- 1780 and 1850 cm The exact position of these bands is slightly dependent on the nature of the sample as well as the solvent used. This doublet is usually ascribed to mechanical coupling of carbonyl vibrations. Thus, the high-frequency band is produced by the symmetric (in-phase) stretching mode whereas the low-frequency band is produced by the asymmetric (out-of-phase) mode. The 1780-cm band is very strong and can be conveniently used to estimate the amount of MA in a mixture by quantitative IR ( 1%). The method is quite useful when solutions are examined by IR. In solutions such as chloroform, benzene, etc., MA has been studied in detail and assignments have been made. In the presence of other anhydrides,particularly polyesters,this could be a valuable method. Of course, all standard methods and limitations of quantitative IR determination apply. Infrared spectra of gaseous MA and Raman spectra are also reported. 

Infrared-Active Carbonyl Vibrations in Octahedral Complexes... 

These compounds have infrared spectra that are greatly complicated by harmonics and combination bands in the region of carbonyl group vibrations. 

Infrared IR spectroscopy is quite useful in identifying carboxylic acid derivatives The, carbonyl stretching vibration is very strong and its position is sensitive to the nature of IKT the carbonyl group In general electron donation from the substituent decreases the double bond character of the bond between carbon and oxygen and decreases the stretch mg frequency Two distinct absorptions are observed for the symmetric and antisym metric stretching vibrations of the anhydride function... 

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