Carbonyl Stretching Modes of

A notable case in which the region of the spectmm to be dealt with is known is that of carbonyl ligands in transition metal complexes. The carbonyl ligand stretching modes occur in the range 2100-1700 cm. This region is usually not shared with other functional 

The set of total characters form a reducible representation which is summarized in the first row of Table 5.7. These are obtained by considering an example operation from each class in turn  

The identity operator, as always, leaves all basis vectors unchanged, and we simply count the number in the basis to arrive at a character of 5. 

The C3 axis contains the two basis vectors on the axial carbonyl ligands, and so these remain in place after any C3 rotation. However, the equatorial ligands are moved by either 

The horizontal mirror plane contains the three equatorial ligands, and so reflection simply exchanges fei and bs, giving a total character of 3. 

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The intensities of the infrared-active carbonyl stretching mode of the hexacarbonyl cations [Mn(CO)6] and [Re(CO)6] + have been measured (77). The absolute intensities of the hexacarbonyl cations are in the order [M(CO)6]+ < M(CO)6 < [M(CO)6]-, which corresponds to the reduction of 77-back-bonding from metal to carbonyl as the positive charge on the metal is increased. (34)... 

TABLE 3-XXIV The Effect of the H Bond on the Carbonyl Stretching Mode of Carboxylic Acids... 

Figure 6.4c shows the carbonyl stretching mode of PS after interaction with the P2 protein found in the nervous system. 

In a study of dirithromycin, Stephenson etal. [53] demonstrate how the position of the carbonyl stretching mode of the lactone moiety may be used... 

Ng and Shurvell [108] have applied factor analysis to deconvolve the complex Raman spectra of acetic acid in aqueous solution. As can be appreciated in Fig. 6, up to five different components can be fitted. These were assigned by the authors in the following manner carbonyl stretching mode of the monomer, symmetric C=0 stretch of the cyclic dimer, terminal and hydrogen-bonded carbonyl group from linear dimer and/or polymer, and water bending band. The monomer-cyclic dimer equilibrium constant was calculated as 0.06 mol Vdm at concentrations below 7 M,... 

Figure 7.1.18. The frequency of carbonyl stretching mode of PEEK vs. temperature. [Adapted, by permission, from B H Stuart, D R Williams, Polymer, 36, No.22, 4209-13 (1995).]...

On the other hand, the adsorption of formic acid at a gold electrode gives two bands, one around 1325 cm" and the other one around 1720 cm" The first one can be attributed, for the same reasons as above, to a formate adsorbed species (HCOO)ads, and the second one to adsorption of molecular formic acid, because 1720 cm is the wavenumber of the carbonyl stretching mode of formic acid. 

A -Acyloxy-A -alkoxyamides are characterised by two high frequency double bond absorptions corresponding to the stretching modes of the ester and amide carbonyls. 

The carbonyl stretching frequency of both the keto and enol tautomers can be recognized in the vibrational spectrum of pentane-2,4-dione. The enol has v(C=0) at 1618cm" , generally the dominant peak in the spectrum and more intense than the in- and out-of-phase v(C=0) stretching modes of the keto form, which are found at 1727 and 1707 cm" , respectively. These are identified by their Raman counterparts at 1719 cm" (polarized) and 1697 cm" (depolarized) (Ernstbrunner, 1970). The ratio of absorbances of the enol and the out-of-phase keto bands in the ir was used as an early method of analysis of the keto/enol equilibrium in different solvents (Le Fevre and Welsh, 1949). 

In this second case, the results of the calculations were in good agreement with the experimental data . The organolithium compound with the RC=0 coordinated in the proposed /rs fashion may now explain the significant shift of the carbonyl stretching mode from 2047 cm in n-BuLi—CO to 1635 cm in w-Bu—C(0)Li (equation 1). 

The IR and Raman spectra of esters derived from peroxycarboxylic and peroxycarbonic esters show a band near 860 cm, assigned to a stretching mode of the OO gronp. The band of the carbonyl gronp in these componnds is shifted to higher frequencies by 30-40 cm , as compared to ordinary esters . ... 

FTIR has been mainly used to obtain structural details of films and to monitor intercalation of metal ions into the film structure and the subsequent reactions of the films with dihydrogen chalcogenides. Both transmission (FTIR-T) and reflection-absorbance (FTIR-RA) modes have been utilized. For the most part these studies have involved films of fatty acids with divalent metal ions. The key features of the FTIR spectra of these films include the asymmetric and symmetric stretching modes of the carboxylate group vs(C02-) and va(C02 ), associated with the M2+/carboxylate complex, and the carbonyl stretching mode v(C=0) of the proton-ated fatty acid. The disappearance of the v(C02 ) (1500-1600 cm-1) and appearance of the v(C=0) bands (—1700 cm-1), concurrent with the formation of the metal chalcogenide and regeneration of the fatty acid, have been used to evaluate... 

The geometry of the tricarbonyl cations [Co(CO)3L2]+ has been established, from the infrared-active carbonyl stretching modes [L = PPh3 (240)] and the proton NMR [L = Tdp (158)], to be trigonal bipyramidal with the phosphines disposed trans in the axial positions. 

Alkyl and aryl peroxides display C—C—O absorption in the 1198-1176 cm 1 region. Acyl and aroyl peroxides display two carbonyl absorption bands in the 1818-1754 cm-1 region. Two bands are observed because of mechanical interaction between the stretching modes of the two carbonyl groups. 

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