Absorption band, infrared

Bassignana et al. (85) have studied 2.4-dimethylselenazole, 2.4.5-trimethylselenazole. and 2-methylselenazoline. The main infrared absorption bands observed are summarized in Table X-22. 

The second ring vibration gives rise to a very weak infrared absorption band at 467 cm and to a weak and depolarized Raman line at 470 cm (202, 203) (Table 1-23). 

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

Just as group vibration wavenumbers are fairly constant from one molecule to another, so are their intensities. For example, if a molecule were being tested for the presence of a C—F bond there must be not only an infrared absorption band due to bond-stretching at about 1100 cm but also it must be intense. A weak band in this region might be attributable to another normal mode. 

The presence of ethyl. V-(p-tolylaulfonylmethyl)oarbamate in the reaction product is most readily detected by the N-H infrared absorption band at 3370 cm.". If the nitrosation is incomplete, the reaction with njtrosyl chloride should be repeated on the mixture of compounds, rather than to try and purify the product by crystallization. 

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). 

If we further assume that the vibrational wavefunctions associated with normal mode i are the usual harmonic oscillator ones, and r = u + 1, then the integrated intensity of the infrared absorption band becomes... 

In 1951, Witkop et al. interpreted the infrared spectra of quinol-2-and -4-ones to favor the oxo formulation. Since then, many investigators, especially Mason, have reported that potential a- and y-hydroxy compounds show infrared absorption bands in the vN—H (3500-3360 cm ) and vC—O (1780-1550 cm ) regions of the spectrum and, hence, exist predominantly in the oxo form references to this work appear in Table I. A study of the bands which occur in the NH-stretching region of the infrared spectra of a series of substituted pyrid-2-ones and quinol-2-ones also supported an oxo formulation for these compounds. Detailed band assignments have been published for pyrid-2- and -4-one. Mason has reported that solutions of j8-hydroxy compounds in chloroform or carbon tetrachloride show... 

As mentioned in Section II,B, solutions of y9-hydroxypyridines in the nonpolar solvents chloroform and carbon tetrachloride show sharp infrared absorption bands near 3600 cm indicating that they exist in the hydroxy form. Infrared spectral data also led Mason to conclude that -hydroxypyridines probably exist largely as such in the solid state and exhibit O— 0 hydrogen bonding, a conclusion which is contrary to an earlier proposal favoring a zwitterion structure. 

Earlier studies of 4-aminopyridine 1-oxide were less conclusive. The solid-state infrared spectrum could be interpreted to indicate the existence of both the imino structure and/or, more probably, the amino structure. Comparison of the actual pKa value of 4-aminopyridine 1-oxide wdth the value calculated using the Hammett equation was considered to indicate that the compound existed as such or as an equilibrium mixture with l-hydroxypyrid-4-onimine, the latter possibility being considered the less likely on the basis of resonance and bond energies/ Resonance energy and ultraviolet spectral considerations have been advanced to support the 4-aminopyridine 1-oxide structure/ The presence of an infrared absorption band at... 

Table 19.1 Approximate positions of some infrared absorption bands ...

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. 

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). 

Orlova N. D., Pozdniakova L. A. Profiles of infrared absorption bands and rotational motion of molecules in liquids. Quantum rotation of hydrogen-chloride molecules, Opt. Spectr. 35, 624-7 (1973). [Optika i Spectr. 35, 1074-7 (1973)]. 

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. 

Infrared spectra of gaseous [30, 31], condensed [32] and matrix-isolated S2O have been measured [33], and Raman spectra of the matrix-isolated molecule were reported [15]. In Table 2 the infrared absorption bands of 5 iso-topomers of S2O are listed some bands coincide with other absorptions. 

Reactant and product analyses were obtained from the intensities of infrared absorption bands by successive subtraction of absorptions by known species. Low noise reference spectra for UDMH and several reaction products were generated for this purpose in order to minimize the increase in the noise level of the residual spectrum with each stage of subtraction. 

Let us close this paragraph with MMCT transitions between two ions of the same element, one with the other with d configuration. Jorgensen [56] showed long ago that the simultaneous presence in 12 M hydrochloric acid of pale yellow Ti(IV) and blue Ti(III) yields a dark brownish-purple 1 1 complex with a stronger absorption band than the single constituents have. The broad absorption band has a maximum at 482 nm. The new absorption band is ascribed to a Ti(III)-Ti(IV) MMCT transition. A near-infrared absorption band in titanium-doped AI2O3 seems to be due to the same transition [57]. 

The infrared absorption spectrum of miconazole nitrate was obtained in a KBr pellet using a Perkin-Elmer infrared spectrophotometer. The IR spectrum is shown in Fig. 4, where the principal peaks were observed at 3140, 3070, 2995, 2920, 1566, 1525, 1445, 1385, 1310, 1070, and 710 cm-1. Assignments for the major infrared absorption band are provided in Table 2. Clarke reported principal peaks at 1085, 1319, 827, 1302, 1038, and 812 cm-1 (miconazole nitrate, KBr disc) [2]. 

Table 2. Assignments for the main infrared absorption bands of penicillamine...

The infrared (IR) absorption spectrum of primaquine diphosphate was obtained as KBr disc using a Perkin-Elmer infrared spectrometer. The infrared spectrum is shown in Fig. 4 and the principal peaks are at 2946, 1612, 1469, 1430, 1384, 1200, 1050, 956, 815, and 760 cm-1. The assignments of the infrared absorption bands of primaquine diphosphate are shown in Table 2. Clarke reported the following principal peaks at 1611, 1595, 815, 1230, 1572, and 1170 cm-1 (KBr disk) [2],... 

B, respectively. The infrared absorption bands assignments for sodium valproate and valproic acids are shown in Table 2(A) and (B), respectively. 

A. Assignments for the infrared absorption bands of sodium valproate ... 

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