Structure characteristic infrared frequencies

Hantzsch s proposal is consistent with characteristic infrared vibration frequencies of syn- and a fr-diazoates, suitably labeled with 15N, measured by Kiibler and Liittke (1963) and by an X-ray structure determination of a sy -diazoate by Alcock et al. (1980b). It is appropriate, therefore, to replace the syn/anti by the (Z/E) nomenclature for isomers (Sec. 7.1)... 

Other than the chloro derivative, 2, the drum and ladder compounds are prepared in high yield, > 70%. All are soluble in organic solvents and show characteristic infrared spectra. The drum compounds and A exhibit a symmetrical doublet for the carboxylate stretching frequency, Vqqq, centered near 1550 cm 1 and a single Sn-0 stretch, v Q, near 600 cm-1. In contrast, the open-drum structures, 2 and 3, show an unsymmetrical vcoo doublet in the same region as that for the drums and the presence of two Sn-0 stretches near 600 cm. ... 

The widespread use of infrared spectroscopy at that time was probably due to the observation that many chemical groups absorb in a very narrow range of frequency. Furthermore, within this frequency range, the observed frequency may be correlated to specific chemical structures. For example, aldehydes can be differentiated from ketones by the characteristic stretching frequency of the carbonyl group near 1700 cm-1, and the spectral pattern may be likened to a molecular fingerprint. ... 

By comparisons among the spectra of large numbers of compounds of known structure, it lias been possible to recognize, at specific positions in the spectrum, bands which can be identified as characteristic group frequencies associated with the presence of localized units of molecular structure in the molecule, such as methyl, carbonyl, or hydroxyl groups. Many of these group frequencies differ in the Raman and infrared spectra. 

Does the tentative structure explain each of the characteristic stretching frequencies in the infrared spectrum Does it account for any shifting of frequencies from their usual positions ... 

Infrared (IR) absorption spectroscopy, especially measured by FTIR, is a powerful technique for the physical characterization of pharmaceutical solids.When the structural characteristics of a solid perturb the pattern of vibrational motion for a given molecule, these alterations can be used as a means to study the solid-state chemistry of the system. FTIR spectra often are used to evaluate the type of polymorphism that exists in a drug substance and can be very useful to study the water contained within hydrate species. Solid-state IR absorption spectra often are obtained on powdered solids through the combined use of FTIR and diffuse reflectance detection, and interpreted through conventional group frequency compilations. ... 

Colthup spectra-structure coaelation charts for infrared frequencies in the 4000-600 cm region from Lin-Vien, D., N. B. Colthup, W. G. Fateley, and J. G. Grasselli, The Handbook of Infrared and Raman Characteristic Frequencies of Organic Molecules, Academie Press, New York, 1991. 

Spectra by the Thousands 575 Infrared Spectra 576 Characteristic Absorption Frequencies Ultraviolet-Visible (UV-VIS) Spectroscopy Mass Spectrometry 584 Molecular Formula as a Clue to Structure 589 Summary 590 Problems 593... 

Characteristic absorption frequencies The regions of the infrared (IR) spectrum where peaks characteristic of particular structural units are normally found. 

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. 

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