Tests infrared spectrum

Testing the purity of a compound. If the spectrum of a sample of known purity is available, the presence of impurities in another sample can be detected from the additional bands in its infrared spectrum. 

The progress of the photolysis can be followed either by observing the disappearance of the typical nitrite bands between 1600 and 1680cm (6.25 and 5.95 ju) in the infrared spectrum or by disappearance of the diphenyl-amine-sulfuric acid spot plate test. 

The hydrochloride of (3) holds water rather tenaciously, and the infrared spectrum indicates that the water is covalently bound. Mild oxidation of the cation (3) gives 4-hydroxyquinazoline in high yield and ring-chain tautomerism is excluded on the grounds that quinazo-line does not give a positive aldehyde test in acid solution, 2-Methyl-quinazoline also has an anomalous cationic spectrum and a high basic strength (see Table I), but 2,4-dimethylquinazoline is normal in both these respects, which supports the view that abnormal cation formation entails attack on an unsubstituted 4-position. ... 

Normally, after this time, the /-butyl perbenzoate is completely reacted. It is advisable, however, to check for its presence because distillation of a crude product containing some perester can lead to an explosion. /-Butyl perbenzoate absorbs strongly in the infrared at 5.65-5.70 ju, and examination of the infrared spectrum of the benzene solution is a sufficiently sensitive test. No difficulty has ever been encountered during reactions with norbomadiene. However, unreacted /-butyl perbenzoate has caused a minor explosion with another, less reactive olefin. 

The trapped product gave an immediate test with KI in acetic acid. Its infrared spectrum was similar to that of 3-butene-2-ol with major absorption peaks at 3, 8.7, 9.5, 10.3, and 10.8 microns and minor peaks at 6.3, 7.2, 7.7, 11.6, 12.4, and 12.6 microns. There was no absorption arising from carbonyl. In a 25% solution of hydroperoxide in carbon tetrachloride, the hydroperoxide proton gave rise to a broad band at 8.7 p.p.m. (referred to TMS) in the NMR spectra. 

We conclude this chapter by presenting several examples of deconvolution of real data. Most of these examples represent deconvolutions of data that were used as part of a spectral analysis rather than generated as deconvolution examples or tests. The examples include high-resolution grating spectra, tunable-diode-laser (TDL) spectra, a Fourier transform infrared spectrum (FTIR), laser Raman spectra, and a high-resolution y-ray spectrum. 

As a result, the depth of penetration, or effective pathlength, will be higher the greater X or the smaller the frequency. Therefore, an interferogram (raw infrared spectrum) is a measure of the attenuation of a trans fat test sample of the totally internally reflected infrared light. The interferogram of a reference background material (trans-free fat) is similarly measured. These are subsequently used to obtain an absorption spectrum. 

With these compounds the presence of the halogen will have been detected in the tests for elements. Most acid halides undergo ready hydrolysis with water to give an acidic solution and the halide ion produced may be detected and confirmed with silver nitrate solution. The characteristic carbonyl adsorption at about 1800 cm -1 in the infrared spectrum will be apparent. Acid chlorides may be converted into esters as a confirmatory test to 1 ml of absolute ethanol in a dry test tube add 1 ml of the acid chloride dropwise (use a dropper pipette keep the mixture cool and note whether any hydrogen chloride gas is evolved). Pour into 2 ml of saturated salt solution and observe the formation of an upper layer of ester note the odour of the ester. Acid chlorides are normally characterised by direct conversion into carboxylic acid derivatives (e.g. substituted amides) or into the carboxylic acid if the latter is a solid (see Section 9.6.16, p. 1265). 

The simpler examples are readily hydrolysed in aqueous solution, and therefore react with sodium hydrogen carbonate and also give the ester test they may be confirmed by applying the hydroxamic ester test (Section 9.5.3, p. 1222). Carbonyl adsorption is apparent in the infrared spectrum at about 1820 cm-1 and at about 1760cm-1. It should be noted that aromatic anhydrides and higher aliphatic anhydrides are not readily hydrolysed with water and are therefore effectively neutral (Section 9.5.3, p. 1218). The final characterisation of the acid anhydride is achieved by conversion into a crystalline carboxylic acid derivative as for add halides. 

These compounds are suggested if sulphur is present. If nitrogen is also present the compound may be an aminosulphonic acid. The infrared spectrum will show absorption at 3400-3200 cm -1 (OH str.) and 1150 and 1050 cm-1 (S=0 str. in a sulphonic add) or at 1090cm-1 (S=0 str. in a sulphinic acid). For derivative preparations for sulphonic acids see Section 9.6.26, p. 1284. The presence of an aromatic sulphinic add may be further confirmed by dissolving in cold concentrated sulphuric add and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to formation of a para-substituted aromatic sulphoxide. The reaction is ... 

If the unknown compound gives a positive test with 2,4-dinitrophenylhydrazine it then becomes necessary to decide whether it is an aldehyde or a ketone. The infrared spectrum of the compound should be very informative both aldehydes and ketones show strong absorption at 1740-1700cm-1 (C=0 str.), but only aldehydes exhibit two absorption bands at about 2720 and 2820 cm-1... 

The methoxylation can be carried out by reacting silica with methanol vapor at 300-400°C, or by refluxing silica in methanol (21,36). Because the infrared spectrum of the modified surface is well understood (36) we chose to use this system as a model to test the feasibility of using Raman spectroscopy (21 ) for studying such surface modification procedures. 

The infrared spectrum of a sample in a potassium bromide pellet may be used as an identity test. In such cases, the infrared spectrum of the sample should compare favorably with the moxalactam disodium reference spectrum over the range of 2.5 to 16 microns. 

The infrared spectrum of oxyphenbutazone in nujol mull is presented in Figure 2. An interpretation of the spectrum is given below. The infrared absorption spectrum of oxyphenbutazone is used as an identification test by the B.P. and U.S.P. 

Infrared spectral analysis9 is employed as a check for other impurities which might be present in the molybdenum(IV) chloride. Molybdenum oxychlorides can be easily identified by their characteristic absorptions in the 900-1000-em.-1 region, which is typical of Mo—O groups. In addition, an examination of the far infrared spectrum should show only the characteristic bands of molybdenum(IV) chloride at 404, 350, and 268 cm.-1. These can be distinguished from those of other molybdenum halide species. A test for the presence of molybdenum (III) chloride, which often occurs as a side product in other preparations of molybdenum(IV) chloride, is treatment with 6 N hydrochloric acid. Complete solubility indicates the absence of this chloride. 

Traditionally, data was a single numerical result from a procedure or assay for example, the concentration of the active component in a tablet. However, with modem analytical equipment, these results are more often a spectrum, such as a mid-infrared spectrum for example, and so the use of multivariate calibration models has flourished. This has led to more complex statistical treatments because the result from a calibration needs to be validated rather than just a single value recorded. The quality of calibration models needs to be tested, as does the robustness, all adding to the complexity of the data analysis. In the same way that the spectroscopist relies on the spectra obtained from an instrument, the analyst must rely on the results obtained from the calibration model (which may be based on spectral data) therefore, the rigor of testing must be at the same high standard as that of the instrument... 

Identification The infrared spectrum of a melted sample on a potassium bromide plate exhibits relative maxima at the same wavelengths as those of a typical spectrum as shown in the section on Infrared Spectra, using the same test conditions as specified therein. 

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