Carbonyl stretching 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... 

Infrared Intensities of Metal Carbonyl Stretching Vibrations, 10, 199 Infrared and Raman Studies of w-Complexes, 1, 239 Insertion Reactions of Compounds of Metals and Metalloids, 5, 225 Insertion Reactions of Transition Metal-Carbon o-Bonded Compounds I Carbon Monoxide Insertion, 11, 88... 

Two other publications on Ir (73 keV) Mossbauer spectroscopy of complex compounds of iridium have been reported by Williams et al. [291,292]. In their first article [291], they have shown that the additive model suggested by Bancroft [293] does not account satisfactorily for the partial isomer shift and partial quadrupole splitting in Ir(lll) complexes. Their second article [292] deals with four-coordinate formally lr(l) complexes. They observed, like other authors on similar low-valent iridium compounds [284], only small differences in the isomer shifts, which they attributed to the interaction between the metal-ligand bonds leading to compensation effects. Their interpretation is supported by changes in the NMR data of the phosphine ligands and in the frequency of the carbonyl stretching vibration. 

The polyamides and polyureas exhibited broad, intense N-H stretches around 3300 cm- , a very strong carbonyl stretching vibration was present at 1630 cm- . The amide II band was evident near 1540 cm- . jn addition, sp C-H stretches occurred around 3100 cm- an(j asymmetric and symmetric sp3 c-H stretches at 2950 and 2860 cm- , respectively. The polyurethane showed the carbonyl absorption near 1700 cm-1 and C-0 stretches in the vicinity of... 

Thus, the region 2100-1830 cm 1 can be covered. This allows us to monitor CO(v,J) by resonance absorption and various M(CO)n [n = 3-6] as a result of near coincidences between the CO laser lines and the carbonyl stretching vibrations of these species. The temporal response of the detection system is ca. 100 ns and is limited by the risetime of the InSb detector. Detection limits are approximately 10 5 torr for CO and M(CO)n. The principal limitation of our instrumentation is associated with the use of a molecular, gas discharge laser as an infrared source. The CO laser is line tuneable laser lines have widths of ca. lO cm 1 and are spaced 3-4 cm 1 apart. Thus, spectra can only be recorded point-by-point, with an effective resolution of ca. 4 cm 1. As a result, band maxima (e.g. in the carbonyl stretching... 

Table 9.7 Effect of substituents on the wavenumber of the carbonyl stretching vibration ...

The IR spectrum of the pseudo-geminal 46) 4-acetyl-13-bromo[2.2]para-cyclophane (18) shows a band for the carbonyl stretching vibration at 1663 cm-1. This frequency lies outside the range of frequencies (1666—1668 cm-1) found for the absorption of other isomers and has been attributed by Reich and Cram to transannular Br...C=0 interactions. 

Ultraviolet spectra of benzoic acid in sulphuric acid solutions, published by Hosoya and Nagakura (1961), show a considerable medium effect on the spectrum of the unprotonated acid, but a much smaller one in concentrated acid. The former is probably connected with a hydrogen-bonding interaction of benzoic acid with sulphuric acid which is believed to be responsible for a peculiarity in the activity coefficient behaviour of unprotonated benzoic acid in these solutions (see Liler, 1971, pp. 62 and 129). The absence of a pronounced medium effect on the spectra in >85% acid is consistent with dominant carbonyl oxygen protonation. In accordance with this, Raman spectra show the disappearance in concentrated sulphuric acid of the carbonyl stretching vibration at 1650 cm (Hosoya and Nagakura, 1961). Molecular orbital calculations on the structure of the carbonyl protonated benzoic acid have also been carried out (Hosoya and Nagakura, 1964). 

The additional structure C, which cannot be drawn for an unconjugated carbonyl derivative, implies that the carbonyl band in an enone has more single bond character and is therefore weaker. The involvement of a carbonyl group in hydrogen bonding reduces the frequency of the carbonyl stretching vibration by about 10 cm-. This can be rationalised in a manner analogous to that proposed above for free and H-bonded 0-H vibrations. 

Box 3.2 Carbonyl Stretching Vibrations in Different Functional Groups... 

Co2(CO)6(tppts)2 is a brown-colored solid which is moderately stable in air, but is best handled and stored under an inert gas atmosphere. The compound is very soluble in water and insoluble in organic solvents like toluene or hexane. It exhibits in the 31P NMR (109.3 MHz, D20, 5°Q a singlet at 5 68.8 ppm. The IR displays a strong carbonyl stretching vibration at 1954 cm-1. The significant SO-absorptions are detectable at 1224 (sh, vst), 1200 (vst), 1039 (vst), and 623 (vst) cm-1. The compound has been used for carbonylation of phenyl ethyl bromide21 and on supported aqueous phase catalysts for the hydroformylation of olefins.22... 

The carbonyl stretching vibrations are in agreement with the local CAv symmetry of the M(CO)4 moiety. 

The absorption maxima of the carbonyl-stretching vibration is shifted by 40 to 50 cm-1 to lower wave numbers by introducing a 13C label, which prevents overlap of the two carbonyl bands. 

A specific example concerns the kinetic resolution of 1-phenylethyl acetate, previously used to illustrate the NMR-based ee assay (see Section 9.3.2). The optimal way to proceed is to apply 13C labeling in the carbonyl moiety, i. e., to prepare a pseudo racemate comprising a 1 1 mixture of (.S)-13C-4 and (R)-4 (Section 9.3). Figure 9.7 shows part of the FTIR spectrum of a 1 1 mixture of (R)-4 and (.S)-13C-4, illustrating the anticipated shift of the respective carbonyl-stretching vibration, which allows quantification of the pseudo enantiomers [22]. 

To apply the Lambert-Beer law in calculation of the concentrations of the pseudo-enantiomeric substances, the molar coefficients of absorbance need to be determined. For this purpose, solutions of (R)-4 and (S)-13C-4 in cyclohexane at different concentrations have to be prepared. After measuring the corresponding absorbances at the absorption maxima of the carbonyl-stretching vibration, the molar coefficients of absorbance are calculated by applying the Lambert-Beer law E = e c d (Figure 9.8). 

After preparation of a stock solution (0.200 M) of (R)- 1-phenylethyl acetate ((i )-4) and (S)-( 1 -phenylethyl)-1 -13C-acetate ((b1)-l3C-4) in cyclohexane, the solutions are diluted with cyclohexane to concentrations of 0.180, 0.160, 0.140, 0.120, 0.100, 0.080, 0.060, 0.040, and 0.020M (total volume lmL). The absorbance of the resulting samples is measured with a FTIR spectrometer at the corresponding absorption maxima of the carbonyl-stretching vibration ((i )-4 1751 cm-1 (S)-13C-4 1699 cm-1) with a thickness of the layers of 25.0 pm, performing 32 scans at a resolution of 4 cm-1. The molar coefficients of absorbance are determined by linear regression, with correlation coefficients >0.995. Analysis of synthetic mixtures of the pseudo enantiomers of 1-phenylethyl acetate is performed under the same conditions at a concentration of 0.10 M. 

The monoketone 8 and the diketone 9 are characterized11 by a carbonyl stretching-vibration band at 1765 cm-1 (KBr and acetonitrile). 

A characteristic feature of the infrared spectra of cyclopropanones is the unusual position of the carbonyl stretching vibration. Whereas simple ketones absorb in the region 1725—1705 cm-1 67>, three-membered cyclic ketones exhibit bands in the 1875—1796 cm-1 range (Table 8). 

In the following years, further investigations were conducted on these compounds until, in 1958, the correct formulas (3 and 4) were at last established almost simultaneously by taking into account the carbonyl stretching vibration of 44 and an X-ray structural determination of 3 (R = R = CH3).5... 

Compatible and incompatible polyester - PVC blends have been considered. Examples include systems, poly-X-caprolactone (PCL)/PVC which are compatible [5,28], in the melt and exhibit partial compatibility in solid state and poly-P-propiolactone (PPL)/PVC blends which are known to be incompatible [5, 28]. Figure 5.9 shows the infrared spectra of the carbonyl stretching vibration (in the range 1600-1800 cm-1) for the different blends. 

Specific interactions between PCL and PVC are clearly indicated. In the solid state (Figure 5.9a) the spectrum of neat PCL indicates the presence of crystalline (1724 cm 1) and amorphous (1737 cm"1) bands. At mole ratios up to 2 1 of PVC to PCL, the spectra indicate that in the solid state the blends consist of crystalline and amorphous phases. As the PVC concentration increases, a parallel increase of the intensity of the amorphous band is observed. Moreover, the frequency shifts observed for both the crystalline and amorphous bands as a function of the composition of the blend suggests that specific interactions between the two polymers occur. No shift is observed in the carbonyl stretching vibration of PPL/PVC blends, in the molten state or in the solid state over the entire range of compositions and the two polymers are incompatible [28]. 

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