![]() These waves differ from each other in the length and frequency (Figure 17-1). Due to historical reasons however, we typically discuss IR light in spectroscopy in terms of wavenumbers rather than wavelengths. Electromagnetic spectrum refers to the seemingly diverse collection of radiant energy, from cosmic rays to X-rays to visible light to microwaves, each of which can be considered as a wave or particle traveling at the speed of light. Figure 1: The infrared spectrum of high-density polyethylene (HDPE). The carbonyl stretching absorption is one of the strongest IR absorptions, and is very useful in structure determination as one can determine both the number of carbonyl groups (assuming peaks do not overlap) but also an estimation of which types.Īs with amines, an amide produces zero to two N-H absorptions depending on its type.Īll figures are for the typical case only - signal positions and intensities may vary depending on the particular bond environment. Infrared light is part of the electromagnetic spectrum between visible light and microwaves, with wavelengths ranging from 780 nm to 1 mm. (Note: The absorptions can be seen as several distinct peaks in this region.) H-C-H Asymmetric &. Primary amines produce two N-H stretch absorptions, secondary amides only one, and tetriary none. Hyrdogen-Bonded Hydroxyl Groups" in the Introduction to IR Spectra for more information Typical IR Absorption Frequencies For Common Functional Groups. Alkane C-H bonds are fairly ubiquitous and therefore usually less useful in determining structure.Ībsorption peaks above 3000 cm -1 are frequently diagnostic of unsaturation
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