Characteristic Infrared Absorption Bands

The characteristic IR absorption bands of various types of compounds are listed in Table 12.3, in two complementary formats. 

Type of Compound Bond Type of Vibration Frequency (cm ) (a) Presented alphabetically by type of compound 

Type of Compound Bond Type of Vibration Frequency (cm ) 

Organic Chemist s Desk Reference, Second Edition 

IR spectra can be quite complex because the stretching and bending vibrations of each bond in a molecule can produce an absorption band. Organic chemists, however, do not try to identify all the absorption bands in an IR specttum. They tend to focus on the functional groups. In this chapter, we will look at several characteristic absorption bands so you will be able to tell something about the structure of a compound that gives a particular IR spectrum. 

You can find an extensive table of characteristic functional group frequencies in the Study Area of MasteringCliemistry. When identifying an unknown compound, chemists often use IR spectroscopy in conjunction with information obtained from other spectroscopic techniques. Some of the problems in this chapter and many of those in dliapter 15 provide practice in using information from two or more instrumental methods to identify compounds. 

More energy is required to stretch a bond than to bend it, so absorption bands for stretching vibrations are found in the functional group region (4000-1400 cm ). 

When a bond stretches, the increasing distance between the atoms increases its dipole moment. The intensity of the absorption band depends on the size of this change in dipole moment the greater the change in dipole moment, the more intense the absorption. 

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Character of the deposit (eg) 509 Characteristic infrared absorption bands ... 

APPENDIX 11 CHARACTERISTIC INFRARED ABSORPTION BANDS 839 APPENDIX 12 PERCENTAGE POINTS OF THE f-DISTRIBUTION 840 APPENDIX 13 / -DISTRIBUTION 841 APPENDIX 14 CRITICAL VALUES OF 0 (/> = 0.05) 842 APPENDIX 15 CRITICAL VALUES OF THE CORRELATION COEFFICIENT p (P = 0.05) 842... 

Subsequent tables cover important titration methods (Table 17), useful 13C-NMR data for the analysis of LAB/LAS (Table 18), molecular fragments of alkylbenzenes (Table 19), and characteristic infrared absorption bands of an LAB/LAS molecule (Table 20). 

Characteristic Infrared Absorption Bands of the Cyclopropyl Ring. J. 

Carbodiimides possess a strong characteristic infrared absorption band in the 4.6-4.8 p region. 

Francis, S. A. Absolute intensities of characteristic infrared absorption bands of aliphatic hydrocarbons. J. chem. Phys. 18, 861—865 (1950). 

TABLE 1.4 Assignment for the characteristic infrared absorption bands of atorvastatin calcium... 

CR is a polymer with relatively large monomer repeating units that consequently exhibit little vibrational coupling between the chemical units along the chain [85], Infrared analysis [86] showed the following bands cis 1652 cm 1, trans 1660 cm"1 1,2, 925 cm 1 3,4, 883 cm"1. For emulsion polymerisation addition is almost entirely 1,4 with no more than about 2% 1,2- and 3,4-. Cis 1,4 - CR exhibits characteristic infrared absorption bands at 847, 1652, 3025 and 3282 cm 1 (C = C overtone). The corresponding trans bands are at 822, 1660, 3018 and 3295 cm 1. Typical CR has 78%-96% trans, 1,4 18% cis 1,4,... 

As expected for silica-alumina as a mixed oxide (see also Section IV.B.5), the PyH+ and PyL species are observed simultaneously (160, 205,206,221-223). Two distinct types of Lewis acid sites could be detected (19b mode at 1456 and 1462 cm-1, respectively) on a specially prepared aluminum-on-silica catalyst (160). On water addition, the Lewis sites can be converted into Br nsted sites (160, 205, 221), The effect of Na+ ions on the acidity of silica-aluminas has been studied by Parry (205) and by Bourne et al. (160). It can be concluded from Parry s results that Na+ ions affect both types of acid sites, so that alkali poisoning does not seem to eliminate the Br nsted sites selectively. For quantitative determination of the surface density of Lewis and Br nsted acid sites by pyridine chemisorption, one requires the knowledge of at least the ratio of the extinction coefficients for characteristic infrared absorption bands of the PyH+ and PyL species. Attempts have been made to evaluate this ratio for the 19b mode, which occurs near 1450 cm-1 for the PyL species and near 1545 cm-1 for the PyH+ species (160,198,206,221,224,225). The most reliable value as calculated from the data given by Hughes and White (198) seems to be... 

IR spectra of the PA/EPDM blends indicated that the blends contain both EPDM and polyacetylene moieties. It was found that the polyacetylene was present in predominantly trans-configuration, as evidenced by a characteristic infrared absorption band at 1015 cm-1 (10). Furthermore, there was no evidence that any polyacetylene moieties were grafted onto the unsaturated sites of EPDM rubber. This was corroborated by an extensive extraction experiment. Virtually quantitative amounts of EPDM could be extracted from the blend with toluene. IR spectra of the fully recovered EPDM were identical to those of the virgin EPDM. 

Figure 17.3 shows an annotated spectrum of propanoic acid. Nitriles show an intense and characteristic infrared absorption band near 2250 cm that arises from stretching of the carbon—nitrogen triple bond. 

Characteristic Infrared Absorption Band Range of Various Biologically Important... 

Solvent for electrolytes that are to be studied spectroscopically need themselves to be transparent for the light of the wavelengths (for UV and visible light) and wavenumbers (for infrared light and Raman spectroscopy) employed for this purpose. The solvents dealt with here are all colorless when pure but have a UV cut-off that ought to be noted. The functional groups of the solvent molecules have characteristic infrared absorption bands that ought to be avoided when solutes in the solvents are to be studied by infrared or Raman spectroscopy. Table 3.12, mostly adapted from [1], shows the appropriate windows at which the solvents are sufficiently transparent. 

The carbonyl (CO) and hydroxyl (OH)/hydroperoxide (OOH) frequencies are the best known of the characteristic infrared absorption bands formed upon photo-oxidative degradation of polymers. These strong bands fall in regions of the spectra where few other absorptions are found. 

Among the vibrational modes of a molecule (or a part of it) adsorbed onto the metal surface, only those modes having transition dipole moments perpendicular to the metal surface can interact with the infrared ray polarized parallel to the plane of incidence, thereby giving rise to characteristic infrared absorption bands. The vibrational modes which have transition dipole moments parallel to the metal surface cannot be observed in the reflection-absorption infrared spectrum. These reflection-absorption phenomena are sometimes referred to as the surface selection rule. 

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