Functional groups: chemical identification

Fourier transform IR spectroscopy Vibrational frequencies of chemical bonds, qualitative and quantitative identification of functional groups Chemical changes during gelation, drying, and firing... 

The two most useful supplementary techniques for the light microscope are EDS and FTIR microscopy. Energy dispersed x-ray systems (EDS) and Eourier-transform infrared absorption (ETIR) are used by chemical microscopists for elemental analyses (EDS) of inorganic compounds and for organic function group analyses (ETIR) of organic compounds. Insofar as they are able to characterize a tiny sample microscopically by PLM, EDS and ETIR ensure rapid and dependable identification when appHed by a trained chemical microscopist. 

Solvent selection ana screening approaches can be divided into two levels of analysis. The first level focuses on identification of functional groups or chemical famihes that are hkely to give favorable solvent-key component molecular interactions. The second level of analysis identifies and compares individual-candidate solvents. The various methods of analysis are described briefly and illustrated with an example of choosing a solvent for the methanol-acetone separation. 

Until the second half of the twentieth century, the structure of a substance—a newly discovered natural product, for example—was determined using information obtained from chemical reactions. This information included the identification of functional groups by chemical tests, along with the results of experiments in which the substance was broken down into smaller, more readily identifiable fragments. Typical of this approach is the demonstration of the presence of a double bond in an alkene by catalytic hydrogenation and subsequent determination of its location by ozonolysis. After-considering all the available chemical evidence, the chemist proposed a candidate structure (or structures) consistent with the observations. Proof of structure was provided either by converting the substance to some already known compound or by an independent synthesis. 

Chemical separations may first be accomplished by partitioning on the basis of polarity into a series of solvents from non-polar hexane to very polar compounds like methanol. Compounds may also be separated by molecular size, charge, or adsorptive characteristics, etc. Various chromatography methods are utilized, including columns, thin layer (TLC) gas-liquid (GLC), and more recently, high pressure liquid (HPLC) systems. HPLC has proven particularly useful for separations of water soluble compounds from relatively crude plant extracts. Previously, the major effort toward compound identification involved chemical tests to detect specific functional groups, whereas characterization is now usually accomplished by using a... 

UV/VIS spectrophotometry can be used to determine many physico-chemical characteristics of compounds and thus can provide information as to the identity of a particular compound. Although UV/VIS spectra do not enable absolute identification of an unknown, they are frequently used to confirm the identity of a substance through comparison of the measured spectrum with a reference spectrum. However, UV spectrophotometry is not highly specific, and can obviously only be applied to polymer additives which are absorbers of UV radiation, i.e. contain chromophoric groups. Both UV and IR monitor functional entities rather than the entire molecular structure. A functional group s proximity to other electropositive or electronegative structures in a molecule affects the absorbance spectrum, allowing one to infer some details of molecular structure. 

Peak position Chemical shift S (ppm) (absolute Hz) Functional group identification... 

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

The subject of this article is the discussion of the functional groups on various surfaces, their chemical identification, and possible chemical reactions with these groups. 

Feldman HJ, Dumontier M, Lng S et al. (2005) CO a chemical ontology for identification of functional groups and semantic comparison of small molecules. FEES Lett 579 4685-4691... 

One of the main routine uses of infrared spectroscopy is identification of specific functional groups present in an unknown molecule and, as a result, further characterization of the unknown. By far the most common example involves the carbonyl group. Location of a strong band in the infrared in the vicinity of 1730cm is almost certain proof that carbonyl functionality is present. This confidence is based on the fact that the characteristic frequency (the CO stretch in this case) is isolated, that is to say, it is sufficiently far removed from the other bands in the infrared spectrum to not be confused with them. It also assumes that carbonyl groups in different chemical environments will exhibit similar characteristic... 

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