Absorption bands compounds

Reactions of 44 with alkali and alkaline-earth metal cations are accompanied by considerable displacement of tautomeric equilibrium toward enolimine complexes 45 K. The intensity of the absorption maximum at 480 nm (corresponding to the tautomer K) in the electronic spectra decreases by 25% for alkaline-earth and 15% for alkali metal cations with the subsequent increase of intensity of the 420 nm absorption band. Compound 44 showed high sensitivity for Cu and Co " " ions. Acetonitrile and dimethyl sulfoxide solutions of 44 exhibit strong fluorescence with maximum at 530 nm. Addition of Cu " and Co " " leads to the formation of chelates 46 demonstrating pronounced naked-eye CHEQ effect the fluorescence intensity decreased by a factor of 39 and 33, respectively, without any appreciable shift of the emission maximum (Figure 10.30). 

Table VIII. The compounds selected are as typical as possible, but it must be remembered that there are many environmental factors that produce changes in the location of the absorption bands. These displacements are usually of the order of a few mp., but in some cases they are so great as to move the absorption band into a completely different region of the spectrum.

Gr. prasios, green, and didymos, twin) In 1841 Mosander extracted the rare earth didymia from lanthana in 1879, Lecoq de Boisbaudran isolated a new earth, samaria, from didymia obtained from the mineral samarskite. Six years later, in 1885, von Welsbach separated didymia into two others, praseodymia and neodymia, which gave salts of different colors. As with other rare earths, compounds of these elements in solution have distinctive sharp spectral absorption bands or lines, some of which are only a few Angstroms wide. 

On the basis of the studies described in the preceding chapters, we anticipated that chelation is a requirement for efficient Lewis-acid catalysis. This notion was confirmed by an investigation of the coordination behaviour of dienophiles 4.11 and 4.12 (Scheme 4.4). In contrast to 4.10, these compounds failed to reveal a significant shift in the UV absorption band maxima in the presence of concentrations up to one molar of copper(ir)nitrate in water. Also the rate of the reaction of these dienophiles with cyclopentadiene was not significantly increased upon addition of copper(II)nitrate or y tterbium(III)triflate. 

The determination of an analyte s concentration based on its absorption of ultraviolet or visible radiation is one of the most frequently encountered quantitative analytical methods. One reason for its popularity is that many organic and inorganic compounds have strong absorption bands in the UV/Vis region of the electromagnetic spectrum. In addition, analytes that do not absorb UV/Vis radiation, or that absorb such radiation only weakly, frequently can be chemically coupled to a species that does. For example, nonabsorbing solutions of Pb + can be reacted with dithizone to form the red Pb-dithizonate complex. An additional advantage to UV/Vis absorption is that in most cases it is relatively easy to adjust experimental and instrumental conditions so that Beer s law is obeyed. 

Description of Method. Quinine is an alkaloid used in treating malaria (it also is found in tonic water). It is a strongly fluorescent compound in dilute solutions of H2SO4 (f = 0.55). The excitation spectrum of quinine shows two absorption bands at 250 nm and 350 nm, and the emission spectrum shows a single emission band at 450 nm. Quinine is rapidly excreted from the body in urine and is easily determined by fluorescence following its extraction from the urine sample. 

Iron Porphyrins. Porphyrias (15—17) are aromatic cycHc compouads that coasist of four pyrrole units linked at the a-positions by methine carbons. The extended TT-systems of these compounds give rise to intense absorption bands in the uv/vis region of the spectmm. The most intense absorption, which is called the Soret band, falls neat 400 nm and has 10. The TT-system is also responsible for the notable ring current effect observed in H-nmr spectra, the preference for planar conformations, the prevalence of electrophilic substitution reactions, and the redox chemistry of these compounds. Porphyrins obtained from natural sources have a variety of peripheral substituents and substitution patterns. Two important types of synthetic porphyrins are the meso-tetraaryl porphyrins, such as 5,10,15,20-tetraphenylporphine [917-23-7] (H2(TPP)) (7) and P-octaalkylporphyrins, such as 2,3,7,8,12,13,17,18-octaethylporphine [2683-82-1] (H2(OEP)) (8). Both types can be prepared by condensation of pyrroles and aldehydes (qv). 

The most powerful method for stmcture elucidation of steroid compounds during the classical period of steroid chemistry (- 1940 1950s) was ir-spectroscopy. As with the ultraviolet spectra, data collected on the infrared spectra of steroids are available in several books, spectmm atiases, and review articles (265,266). Unlike ultraviolet spectroscopy, even the least substituted steroid derivatives are relatively rich in characteristic absorption bands in infrared spectroscopy (264). 

Cerous salts in general are colorless because Ce " has no absorption bands in the visible. Trivalent cerium, however, is one of the few lanthanide ions in which parity-allowed transitions between 4f and Sd configurations can take place and as a result Ce(III) compounds absorb in the ultraviolet region just outside the visible. 

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. 

The molecular ellipticity is analogous to specific rotation in that two enantiomers have exactly opposite values of 0 at every wavelength. Two enantiomers will thus show CD spectra having opposite signs. A compound with several absorption bands may show both... 

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). 

The behaviours of CD and ORD curves in the vicinity of an absorption band are collectively known as the Cotton effect after the French physicist A. Colton who discovered them in 189S. Their importance in the present context is that molecules with the same absolute conhguration will exhibit the same Cotton effect for the same d-d absorption and, if the configuration of one compound is known, that of closeiy similar ones can be established by comparison. 

Thiophenes substituted with groups such as alkyl, halogens, OCH3, and SCH3 show small but characteristic differences between 2- and 3-substituted compounds. In these cases, however, it is the 2-isomer which shows the less complex spectrum. Thus, 2-substituted alkylthio-phenes and halothiophenes show a single band with greater extinction than the 3-isomers whose spectra exhibit two peaks in a broadened absorption band. These differences are also present in the spectra of 2,5- and 3,4-dihalosubstituted compounds. In 2-substituted thiophenes, the intensity of the band varies inversely as the electronega-... 

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... 

Shugar and FoxS " reported that 4-ethoxypyrimidin-2-one exists in the 0X0 form 102 since its ultraviolet spectrum is different from that of 103. They further claimed that the isomeric compound, 2-ethoxy-4-hydroxypyrimidine, existed in the hydroxy form (104) however, reexamination of the ultraviolet spectral data suggests that this unlikely conclusion may be incorrect, and the infrared spectrum of 104 does, indeed, show a carbonyl absorption band. 2-Methylthiopyrim-idin-4-one has been reported to exist in the hydroxy form, but this to appears unlikely. 

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... 

Substituted pyridopyrimidines show the same tluee principal (77 77 ) absorption bands as the parent compounds but with batho-chromic shifts which may obliterate hands du e to the n n transitions. 

Brown and Mason converted the hydrates into alcoholates by boiling them with alcohol. The hydrate and alcoholate of 6,7-diethyl-2-hydroxypteridine showed two N—H absorption bands in the infrared, and, when either compound was heated at 120° in vacuo, the band of higher frequency was strongly reduced in intensity. These results led to a new test for covalent hydration the substance is refluxed with... 

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