Infrared characteristic bands

Table 2 Infrared characteristic bands and their assignments.

Chart 1.1 Regions of strong solvent absorptions in the 7 Chart 17.1 Infrared - characteristic bands of phosphorus 230... 

Chari 1.6 Infrared - characteristic bands of groups and 22 Chart 22.3 Infrared - band positions of complexes, ligands 295... 

Chart 16.1 Infrared - characteristic bands of sulphur 210 Figure ll.l Characteristic aromatic bands 900-600 cm" 157... 

TABLE III Selected Near Infrared Characteristic Bands... 

H. Yoshida, and K. Inazuka, 1964. Infrared characteristic bands of highly dispersed silica. 

Determination of purity. The ultraviolet and visible absorption is often a fairly intensive property thus e values of high intensity bands may be of the order of 10 -10 . In infrared spectra e values rarely exceed 10 . It is therefore often easy to pick out a characteristic band of a substance present in small concentration in admixture with other materials. Thus small amounts of aromatic compounds can be detected in hexane or in cyclohexane. 

Whether the molecule is a prolate or an oblate asymmetric rotor, type A, B or C selection mles result in characteristic band shapes. These shapes, or contours, are particularly important in gas-phase infrared spectra of large asymmetric rotors, whose rotational lines are not resolved, for assigning symmetry species to observed fundamentals. 

A powerful characteristic of RAIR spectroscopy is that the technique can be used to determine the orientation of surface species. The reason for this is as follows. When parallel polarized infrared radiation is specularly reflected off of a substrate at a large angle of incidence, the incident and reflected waves combine to form a standing wave that has its electric field vector (E) perpendicular to the substrate surface. Since the intensity of an infrared absorption band is proportional to / ( M), where M is the transition moment , it can be seen that the intensity of a band is maximum when E and M are parallel (i.e., both perpendicular to the surface). / is a minimum when M is parallel to the surface (as stated above, E is always perpendicular to the surface in RAIR spectroscopy). 

Bohlmann et al. (118-121) observed that an infrared absorption band between 2700-2800 cm is characteristic of a piperidine derivative possessing at least two axial carbon-hydrogen bonds in antiperiplanar position to the free-electron pair on the nitrogen atom. The possibility of forming an enamine by dehydrogenation can be determined by this test. Compounds which do not fulfill this condition cannot usually be dehydrogenated (50, 122,123). Thus, for example, yohimbine can be dehydrogenated by mercuric acetate,whereas reserpine or pseudoyohimbine do not react (124). The quinolizidine (125) enamines (Scheme 4), l-azabicyclo(4,3,0)-nonane, l-azabicyclo(5,3,0)decane, l-azabicyclo(5,4,0)undecane, and l-azabicyclo(5,5,0)dodecane have been prepared in this manner (112,126). 

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. 

To use KBr discs for quantitative measurements it is best to employ an internal standard procedure in which a substance possessing a prominent isolated infrared absorption band is mixed with the potassium bromide. The substance most commonly used is potassium thiocyanate, KSCN, which is intimately mixed and ground to give a uniform concentration, usually 0.1-0.2 per cent, in the potassium bromide. A KBr/KSCN disc will give a characteristic absorption band at 2125 cm 1. Before quantitative measurements can be carried out it is necessary to prepare a calibration curve from a series of standards made using different amounts of the pure organic compound with the KBr/KSCN. A practical application of this is given in Section 19.9. 

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). 

Infrared absorption bands of S (n>2) complexes are usually of low intensity, while the Raman spectra often show intense and characteristic hnes. However, the assignments are difficult because of their complexity. The absorptions in electronic spectra are often assigned to intrahgand transitions, and it is known that the increasing length of the polysulfido chain leads to an increasing red shift of the absorption band. 

The infrared spectra were recorded after equilibrating the reduced and evacuated solids with an excess of pyridine vapor and further evacuation at various temperatures. After evacuation at 423 K there is no more physically adsorbed pyridine. There is no characteristic band of pyridine adsorbed on Bronsted acid sites (no appearance of the 19b vibration at 1540-45 cm" ) [11,12]. The OH groups observed on the solids are thus non acidic. The existence of Lewis acid centers (coordinatively unsatured Al " or Zr ) is proven by the presence of the 19b vibration at 1440-50 cm" and of the 8a vibration at 1610-1620 cm". The absorbances of the 1440-50 cm" band show that the acidity difference between the Pd/Al203 and PdyZr02 solids is not significant. 

The infrared (IR) spectrum of 10 exhibited a /NH at 3220cm-1 and a strong band at 1720cm-1 corresponding to vq=q, whereas in the case of compound 11 the IR spectrum showed a characteristic bands at 3210 and 1650 cm-1 due to the corresponding NH and CO, respectively <1989JOC3062>. 

Table I. A Comparison of the Characteristics of Infrared Vibrational Bands Arising from Bulk Solution Species and Adsorbed Species...

In 1999, Binet et al.395 published a review on the response of adsorbed molecules to the oxidized/reduced states of ceria. In light of recent infrared studies on ceria, the assignments for OH groups, methoxy species, carbonate species, and formates are highly instructive. The OH and methoxy species have been briefly discussed. Characteristic band assignments of carbonate and formate species are provided below, the latter formed form the dissociative adsorption of formic acid, the reaction of CO with H2-reduced ceria surface, or via selective oxidation of methanol. Formate band intensities were a strong function of the extent of surface reduction of ceria. 

Characteristic Infrared Absorption Bands of the Cyclopropyl Ring. J. 

The infrared spectra of dihydrodiazepinium salts are complex but there are several characteristic bands [68JCS(B)I536]. In the 3000 cm region i>i4H shows as a medium to strong band at 3500 cm. Hydrogen atoms at the 5-, 6-, or 7-positions give rise to a weak i>c.h band at 3050-3100 cm" alkyl vc-H bands at 2900 cm" are also weak. When there are hydrogen... 

The infrared spectrum of procaine hydrochloride, presented in Figure 4, was obtained in a KBr pellet and recorded on a Pye-Unicam model SP 1025 infrared spectrophotometer. The assignments of the characteristic bands in the infrared spectrum is given in Table 2 ... 

Infrared spectra of some disubstituted oxadiazoles are reported to show characteristic bands of this heterocyclic system. 

The infrared spectrum in the carbonyl stretching region is very useful in characterizing these complexes (Table I). Three infrared active bands are predicted 18 however, limited solubility may preclude observation of the weaker bands. Dimer formation is easily detected by the presence of characteristic bands.12... 

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

The infrared spectrum (Fig. 5b) shows that all recreated silanols have reacted and that characteristic bands appear in the 1600 -1300 cm 1 region, due to the acac ligand... 

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