Infrared absorptions associated with

Table 3.10 Infrared Absorptions Associated with Hydrogen Bonding...

Besides confirming the types of infrared absorption associated with a and P forms, which have been described for other proteins and polypeptides (2, 31) the spectra of Fig. 14C demonstrate an a-type phase which is more difficult to transform by stretching than the crystalline phase. It corresponds to the K3 phase of wool keratin (6) the 8-type absorption at 1630 cm. arises from the crystalline phase K2 and possibly some Ki phase which transforms along with or before the crystalline material. 

This reduces to Ai + E. Ai has the same symmetry as the Cartesian coordinate z and is therefore IR active. E has the same symmetry as the x and y coordinates together and is also IR active. It represents a degenerate pair of vibrations, which appear as one absorption band, as shown in Figure 4.28. Infrared absorptions associated with specific bonds are commonly designated as vlXY), where XY is the bond that contributes most significantly to the vibrational modes responsible for the absorptions. In Figure 4.28, the v(CO) spectrum features absorptions at 1920 and 1790 cm". ... 

We now need to take up the vibrational contributions to the absorption and the Raman correlation functions. Ordinarily, the motion associated with a normal mode is not appreciably coupled either with the orientation of the molecule, or with other normal modes in the same molecule or in other molecules. (Treatments of this coupling do exist, but are too advanced for present purposes.) When these assumptions are made, the spectral time-correlation functions simplify greatly. For example, for the infrared case, the pure rotational part is augmented by a series of terms, one for each normal mode. We can consider these separately since, as mentioned above, they usually correspond to vibration-rotation bands which in favorable cases are isolated spectral features that can be Fourier transformed or otherwise analyzed independently from the other bands. The time-correlation function for the infrared absorption associated with the Vth normal mode is thus written as... 

Figure 13.22 Infrared absorption associated with the carbonyl stretching band showing dichroism due to uniaxial orientation along the director (0°).

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... 

The 1036 cm 1 absorption band together with the 1041 cm"1 absorption associated with the trans isomer appear to provide a particularly reliable measure of relative cis versus trans concentrations281"12. Only by disregarding the k, value based on the 1036 cm"1 absorption data and by passing over probable systematic errors in the estimation of k, from infrared data at 846 cm 1 was it possible to conclude that kn is very much greater than k and that the double rotation mechanism predominates by a substantial factor. 

In their original paper (2) on the structure of Fe5C(CO)l5, Dahl and co-workers assigned two bands in the infrared spectrum of hydrocarbon solutions of the cluster, at 790 and 770 cm-1, to vFeC modes. This assignment has been confirmed by a recent study of the infrared spectra of the series M5C(CO)15, (M = Fe, Ru, Os) (78). The room temperature spectra of the compounds (Table II) in the solid state are quite similar to each other, comprising three bands assigned as the a, and e modes (split in the solid state) expected for the C4 symmetry of the isostructural clusters. At low temperature the ruthenium and osmium clusters exhibit five absorptions associated with M-C stretches, whereas the iron cluster retains its room temperature spectrum. This is ascribed to the presence of two types of cluster molecule in the crystal lattices of the ruthenium and osmium clusters which are isostructural with, but not isomorphous with, the iron analog in which all the molecules are identical. 

Fig. 15.4 Infrared spectrum of the carbonyl region for Fe(CO)j showing the absorptions associated with the AJ and E stretching vibrations.

The distinctive absorptions associated with the ds-Re02 grouping appear at 923 (s) and 843 (s) cm in the infrared spectrum of the complex (Nujol mull). The PNMR spectrum exhibits a single resonance at -f 4.57 ppm (relative... 

Partial desilylation does not seem to be associated with the formation of 2-4 linkages in the polymer chains. The IR absorption spectra of both polymers pSiTh-1 and pSiTh-2 do not show a vc h vibration at 3100cm", characteristic of the presence of an hydrogen atom at the a carbon of the thiophene ring (Schemes 14.33 and 14.34). This was further confirmed by an examination of the infrared spectrum of a pSiTh-3 polymer obtained from a monomer with a deuterium at the 2 position (Scheme 14.33). No absorption associated with the vc-d vibration (2200 cm" ) was observed. This, together with the absence of absorption at 569 cm" due to the yc-o vibrational mode, is... 

The sp -hybridi2ed C—H bonds in saturated hydrocarbons such as octane (Figure 2.10a) absorb infrared radiation in the 2850—3000 cnr region. The sp -hybridized C—H bonds in alkenes such as 1-octene absorb energy at 3080 cnr . This peak appears separately from the absorptions associated with the sp -hybridized C—H bonds in this molecule (Figure 2.10b). The isomeric cyclooctane would not have the 3080 cm" absorption. An sp-hybridized C—H bond in a molecule such as 1-octyne (Figure 2.10c) absorbs infrared radiation at 3320 cm". An isomeric bicyclic hydrocarbon with no multiple carbon-carbon bonds, and hence no sp - or sp-hybridized carbon atoms, would have absorptions only in the 2850-3000 cm" region. 

Infrared. It can be seen from Fig. 4 that infrared radiation is of an energy suitable for the stimulation of vibrational absorption that occurs within a single electronic level. For gas-phase samples, vibrational bands can be divided into a series of closely spaced absorptions associated with molecular rotational energy levels however, these are not usually observed. Even so, the infrared absorption spectrum for most solid and liquid samples is complex and contains many sharp maxima and minima associated with well-defined vibrational energy levels. 

Infrared The absorptions of interest m the IR spectra of amines are those associated with N—H vibrations Primary alkyl and arylammes exhibit two peaks m the range 3000-3500 cm which are due to symmetric and antisymmetric N—H stretching modes... 

Infrared absorption studies have shown that correlates with an absorption at 3 p.m associated with an OH-stretching frequency (20). Indeed, infrared absorption provides a useful tool for evaluation in rapid production quaUty control. Infrared and other studies show that degradation is caused by proton inclusion in the grown quartz. 

Infrared spectroscopy can also be used incisively to identify the six main varieties of asbestos fibers. Specific absorption bands in the infrared spectmm can be associated with the asbestos fibers, first in the 3600 3700 cm range (specific hydroxyl bands) and, second, in the ranges 600—800 and 900 1200 cm (specific absorption bands for various siUcate minerals (10)). 

If we further assume that the vibrational wavefunctions associated with normal mode i are the usual harmonic oscillator ones, and r = u + 1, then the integrated intensity of the infrared absorption band becomes... 

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