Ureas, infrared frequencies

In this section, we discuss the identification process and the chemical structures of polymers as obtained from their infrared and Raman spectra. Many polymers have common features, and it is convenient to segregate polymers into groups, such that the characterization of the polymers in a group can be discussed together. A popular method for classifying polymers is by their modes of application. For instance, some polymers, such as polyvinyl acetate, polystyrene, and nylons, are classified as thermoplastics, while urea, melamine, and epoxide resins are classified as thermosets or thermosetting resins. In this chapter we will use a different approach to classify the polymers, based on their similarity of chemical structure. This enables us to utilize the correlation between the functional groups of polymers and their characteristic infrared and Raman frequencies. 

One of the most powerful arguments in favor of A -protonation has been the appearance of a band in the high-frequency carbonyl region in amide salts. However, this band does not undergo an isotope shift (326) in the salts of oxygen-18 labeled urea or propionamide relative to the unlabeled compounds. It is therefore not due to the carbonyl stretching frequency in the salt as had previously been thought. Kumler (214) has also interpreted the infrared spectra of... 

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