Raman frequencies of carbonyl bands

TABLE 7.33 Raman Frequencies of Carbonyl Bands Continued)... 

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). 

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 . ... 

Although not all bands can be assigned in the 300-700 cm region of these complex systems, certain bands can still be associated with the appropriate symmetry species. For instance, the e bands of many carbonyl compounds were split in the solid state spectra and could consequently be identified (5, 25, 80). Also, where Raman data were available, e.g., for the derivatives Ni(CO)4 L , the ai fundamentals were readily identified from polarization measurements (31, 35, 43, 131, 222). Finally, correlation curves of the MC-stretching frequencies of the derivatives Ni(CO)4 L have also been plotted and, in an analogous way to those for the CO-stretching frequencies, used to establish certain assignments (35, 43, 131, 222). 

Hydantoins show two bands in the carbonyl region at about 1720 and 1780 cm-1. However, their interpretation has been the subject of controversy. The low-frequency band has been attributed both to the C-4168 and the C-2 carbonyl group.169 Infrared and Raman spectra have also been interpreted in terms of carbonyl coupling similar to that found in imides.170 Other studies have confirmed this coupling.171... 

Q What would be the wavelength of the Raman band corresponding to a carbonyl group frequency of 1650 cm , assuming a laser wavelength of 546.0 nm ... 

Physical Properties.—In a comparative study of the i.r. and Raman spectra of oxazolidine- (322 X = O), thiazolidine- (322 X = S) and selenazo-lidine-2,4-diones (322 X = Se), the observations are interpreted in terms of coupling between the carbonyl groups, identical to that shown by cyclic imides such as hydantoins (323), The carbonyl band of low frequency... 

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