Infrared spectrum characteristics

Besides local geometries, the intelligent sketchpad can contain any local properties, including bond types and strengths, chromophore optical spectra, and nuclear magnetic resonance and infrared spectra characteristic of a local chemical environment. 

This reaction is general and proceeds smoothly and quantitatively in light petroleum at room temperature each triple bond of a diync reacts independently. The complexes are diamagnetic, and show bands in their infrared spectra characteristic of terminal carbonyl groups, but no bands due to bridging carbonyl groups or a C C stretching vibration. 

Characterization of the structures of these products is facilitated by the study carried out on the model compounds. In the infrared spectra, characteristic N—H absorptions are found at 3320 cm.-1 and of C=0 at 1705 cm.-1, with a shoulder at 1650 cm.-1 (C=C). The NMR spectrum in CC14 confirms the unsaturated nature of the products through the existence of a mass of peaks at t = 5.0 probably caused by the superposition of Structures E. The presence of the structural units E4 cannot be confirmed with certainty because of the unsatisfactory quality of the NMR spectrum. However, the infrared spectrum of the product reduced with LAH shows the presence of C=CH2. This reduced product is slightly soluble in aqueous acids from which it precipitates on adding ammonia its solubility in organic solvents is very much less than that of the previous product, and it was not possible to study it by NMR. 

Iododiborane(6) condenses in a vacuum system as a colorless liquid. It hydrolyzes rapidly and should be kept out of contact with light and mercury. It should be stored at -196°. The vapor pressure of B2HSI is 70 torr at 0°. Both B2HSI and B2DSI are best characterized by their infrared spectra. Characteristic infrared bands (cm ) are as follows ... 

The peptide structure of proteins is indicated by many lines of evidence hydrolysis of proteins by acids, bases, or enzymes yields peptides and finally amino acids there are bands in their infrared spectra characteristic of the amide group secondary structures based on the peptide linkage can be devised that exactly fit x-ray data. 

Jalsovszky, G. and Holly, G., Pattern Recognition Applied to Vapour-Phase Infrared Spectra Characteristics of nuOH Bands, J. Mol. Struct., 175, 263, 1988. 

All the metal-saccharin complexes described here exhibit similar properties. They are found to be non-hygroscopic, stable in air, very soluble in pyridine and N,N-dimethyl formamide, and slightly soluble in cold water. They give almost identical solid state (Nujol) infrared spectra, characteristic peaks of which are 3500-3100 cm 1, s.b[v(0—H) of different types of water molecules present in the complex] 3090 cm 1, s[v(C—H)] 1610 cm , s[v(C=0)] 1570 cm 1, s[v(C—C), mixed with (H—O—H) deformation of lattice water] 1280 cm 1, vs[asymmetric... 

Formula II shows one trans-double bond which is shared with the nickel atom. Furthermore, there are six carbon atoms which are in the state of an -hybridization. Each C atom shares one r-electron with the nickel. (The complex shows the correct molecular weight for NiCi2Hig, and there is no absorption in the infrared spectrum characteristic of double bonds.) This formulation has some relationship to structures which have been recently proposed by different authors (2, 4) for various allylic groups bonded to transition metal carbonyls. 

We cannot overemphasize the importance of paying attention to good thermal connection between the copper block and the sample holder in a vacuum environment, particularly at very low temperatures where the thermal conductivity of most materials is not good. In an experiment in which a sample was mounted carelessly, on cooling to 10 K and illuminating the sample, a gap of about 50 /am opened between the sample and the copper block because of differential thermal expansion. The sample yielded an infrared spectrum characteristic of 320 K, while the copper block remained at 10 K ... 

This general behaviour is characteristic of type A, B and C bands and is further illustrated in Figure 6.34. This shows part of the infrared spectrum of fluorobenzene, a prolate asymmetric rotor. The bands at about 1156 cm, 1067 cm and 893 cm are type A, B and C bands, respectively. They show less resolved rotational stmcture than those of ethylene. The reason for this is that the molecule is much larger, resulting in far greater congestion of rotational transitions. Nevertheless, it is clear that observation of such rotational contours, and the consequent identification of the direction of the vibrational transition moment, is very useful in fhe assignmenf of vibrational modes. 

In the infrared, 2-hydroxycyclobutanone has a carbonyl band at 1780 cm in chloroform solution. Kept in nitrogen-filled screw-capped vials in the freezing compartment of a refrigerator, 2-hydroxyoyolo-butanone slowly but completely solidifies as its dimer. The infrared spectrum of the solid in a KBr disk shows no carbonyl. However, a chloroform solution of the solid does show the characteristic 1780 em band, indicating rapid equilibration with the monomer. 

Fingerprint region (Section 13.20) The region 1400-625 cm of an infrared spectrum. This region is less characteristic of functional groups than others, but varies so much from one molecule to another that it can be used to determine whether two substances are identical or not. 

These structural problems are also insoluble by physical methods alone. The infrared spectrum often gives an unambiguous decision about the structure in the solid state the characteristic bands of the carbonyl or the hydroxyl group decided whether the compound in question is a carbinolamine or an amino-aldehyde. However, tautomeric equilibria occur only in solution or in the liquid or gaseous states. Neither infrared nor ultraviolet spectroscopy are sufficiently sensitive to investigate equilibria in which the concentration of one of the isomers is very small but is still not negligible with respect to the chemical reaction. 

The infrared spectrum of the indenopyrazole 20 contains a band at 7.3/i, (1381 cm" ) which is considered characteristic of the indene... 

The oxaziranes are colorless and they do not absorb in the UV region. Aryl-substituted oxaziranes show only the absorption of the aryl group. The oxaziranes are also transparent in the double bond region of the infrared spectrum, but they show a well developed band near 1400 cm" which has been considered characteristic for oxa-ziranes. ... 

N-Acetylation of Kasugamycinic Acid (9a). A solution of kasugamycinic acid (225 mg.) dissolved in 10 ml. of water was treated with acetic anhydride (0.3 ml.) under cooling sodium bicarbonate was used to keep the pH 7.2 and stirring continued for 30 minutes. The reaction product was passed through Dowex 50W-X2 (H form) and the column was washed with water. The combined filtrate was subjected to lyophilization to afford 234 mg. of a crude N-acetyl derivative. Its infrared spectrum showed strong absorptions at 1740 cm-1 characteristic of oxamic acid group. The N-acetyl derivative (178 mg.) was treated with 40 ml. 

Figure 17.11 Infrared spectrum of cyclohexanol. Characteristic O-H and C-0 stretching absorptions are indicated.

More complicated molecules, with two or more chemical bonds, have more complicated absorption spectra. However, each molecule has such a characteristic spectrum that the spectrum can be used to detect the presence of that particular molecular substance. Figure 14-17, for example, shows the absorptions shown by liquid carbon tetrachloride, CCfi, and by liquid carbon disulfide, CS2. The bottom spectrum is that displayed by liquid CC14 containing a small amount of C. The absorptions of CS2 are evident in the spectrum of the mixture, so the infrared spectrum can be used to detect the impurity and to measure its concentration. 

Except in simple cases, it is very difficult to predict the infrared absorption spectrum of a polyatomic molecule, because each of the modes has its characteristic absorption frequency rather than just the single frequency of a diatomic molecule. However, certain groups, such as a benzene ring or a carbonyl group, have characteristic frequencies, and their presence can often be detected in a spectrum. Thus, an infrared spectrum can be used to identify the species present in a sample by looking for the characteristic absorption bands associated with various groups. An example and its analysis is shown in Fig. 3. 

Tin oxide, Sn02, has unusual physical properties. It is a good electrical conductor. It is highly transparent to the visible and highly reflective to the infrared spectrum. It is deposited extensively by CVD mostly for optical applications. Its characteristics and properties are summarized in Table 11.6. 

Infrared frequencies are characteristic for certain bonds in molecules and they can often be used to identify chemisorbed species on surfaces. The infrared spectrum of CO or NO can sometimes also be used to recognize sites on the surface of a catalyst, as the following example shows. 

Many characteristic molecular vibrations occur at frequencies in the infrared portion of the electromagnetic spectrum. We routinely analyze polymers by measuring the infrared frequencies that are absorbed by these molecular vibrations. Given a suitable calibration method we can obtain both qualitative and quantitative information regarding copolymer composition from an infrared spectrum. We can often identify unknown polymers by comparing their infrared spectra with electronic libraries containing spectra of known materials. 

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