Carbonyl stretching mode

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). 

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 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)... 

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. 

Carbonyl stretching modes and their frequencies for Fe(CO)5. Note that only one component is shown for vioCEO-... 

Diels-Alder reactions have also been studied via the fundamental and the first overtone absorptions of carbonyl stretching modes. Absorbance spectra measured during the cycloaddition of 2 (with R = CCI3) and 3 in CH2CI2 solution at 1000 bar and 95 °C are shown in Fig. 6.7-18. 

The stability of these species (XL a can be sublimed in vacuo at 180 C without decomposition ) is certainly due, in large part, to the bulkiness of the substituted phosphole ring. This bulkiness is well evidenced by the IR spectra of XLb and XLc which show four strong and well resolved metal carbonyl stretching modes indicating that the formal C4 symmetry is lost together with the usual degeneracy of the E mode. 

The carboxylic acid carbonyl frequency is shifted to lower frequency by 1 to 6 percent in carboxylic acid dimers, which is much less than the relative shifts of The mechanical splitting of the symmetric and antisymmetric carbonyl stretching modes is evident in the difference between the Raman and IR spectra of formic acid. Of course the average of these two is of interest, but often only one is measured. 

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

The studies by Miyazawa, Shimanouchi, and Mizushima (1422, 1424) have already been mentioned in the discussion of vt, the in-plane N—H bending mode. The amide I band, a carbonyl stretching mode, shifts downward with Av/v = - -0.028, whereas the amide II band, a mixture of i j(CN) and r6(NH), shifts upward with Av/v = —0.045. Although this upward shift is in the direction expected for Vb, Mizushima et al. feel that the shift should be attributed in part to double bond character induced in the C—bond when the H bond is formed. ... 

IR carbonyl stretching mode, acetone in CHgOH, CHCU, CCI4, hexane. 

Salts were filtered ofiF and the filtrate was concentrated. Recrystallization from pentane at -20°C gave analytically pure orange-yellow crystals of 1 suitable for an X-ray crystallographic study (Figure 1). The infrared spectrum of 1 shows two carbonyl stretching modes at 1908 and 1963 cm, as expected for compounds of the type (ti -C5Me4Et)Fe(CO)2L. The NMR data of 1 are in agreement with the proposed structure (Table 1) and the observations are in accordance with other experimental results [4],... 

TABLE I Carbonyl Stretching Modes (cm-1) (Calibrated against polystyrene)... 

Fig. 4.18 (a) Infrared absorbance spectra measured in the carbonyl-stretching-mode region during the reaction of the phthalimidobutenone 1 with propenylmethylether 2 at a temperature of 50°C and a pressure of 500 bar. (b) Infrared absorbance difference spectra, derived from the absorbance spectra in (a) (see text). 

Group III acceptors are present in the majority of compounds containing I—CO— carbonyls (3,8,31-41). Rare earth acceptors interact similarly with terminal oxygen atoms of carbonyls (9, 53-56). Compounds of these types are presented in Table IV. As with previous examples cited in this article, one of the most diagnostic features of these adducts is the low frequency carbonyl stretching modes characteristic of the E —CO— array (42). 

Other types of data that have been used, though less extensively, to verify the multiple nature of M—CO bonds are the intensities of carbonyl stretching modes,3 the frequencies of metal—carbon stretching modes,4 equilibrium constants for ligand exchange reactions,5 molecular-orbital calculations6 and electronic spectra.7... 

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

Turro, George, and co-workers [70] have also observed and studied an acyl radical in solution by TRIR methods in their investigation of the photochemistry of (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (Scheme 2.4). More recently, Vasenkov and Frei [71, 72] reported the generation of the acetyl radical by photolysis of 1-naphthyl acetate (Scheme 2.5) or pinacolone (Scheme 2.2 R = Me, R = f-Bu) in zeolite NaY. Through the use of step-scan FTIR spectroscopy, they observed a carbonyl stretching mode at 2125 cm , interestingly... 

The carbonyl C=0 stretch mode gives rise to one of the most intense absorption peaks in IR. From the virtual absence of spectral peaks in the C=0 position, it may be concluded that the amount of physical adsorption is small in the present cases. A small shoulder at 1685 cm" was observed for benzaldehyde adsorbed on alumina and was attributed to the carbonyl stretching mode in that instance (19). Some physical adsorption might occur by hydrogen bonding to the hydrated alumina surface (Al-O-H... 0==C0H-) or to benzoate ions on the surface (-COO"... HO-CO-). 

For reliable data, the concentration of the components of the mixture must be determined. Measuring peak Intensities and then relating these values to the amount of each component present is practically impossible by standard analytical techniques for this system. In order to do quantitative analysis, first, frequencies must be found that are unique to each component and, second, Intermolecular Interactions must be at a minimum. Re-examining Figure 3, reveals that only the carbonyl stretching mode at 1685 cm" may be free of overlap. The difficulty presented by these systems (natural rubber-peroxide and polybutadlene-peroxlde) provides a test of the sensitivity of the FTIR spectrometer. 

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

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