Ultraviolet absorption interpreting spectra

Once the FBA has been identified, ultraviolet absorption spectroscopy affords a rapid and accurate method of quantitative analysis. Care must be taken when interpreting the spectra of stilbene-type compounds, since turns to cis isomerisation is promoted by ultraviolet radiation. Usually, however, a control spectrum of the turns isomer can be obtained before the compound undergoes any analytically significant isomerisation. FBAs are often marketed on the basis of strength comparisons determined by ultraviolet spectroscopy. 

As in the case of polypropylene, the question is whether the complex spectrum recorded should be interpreted as arising from alkylic or allylic radicals—i.e., structures XVII and XXVI, respectively. This basic problem could probably be solved by using ultraviolet absorption spectroscopy at liquid nitrogen temperature (9, 10, 11, 12). 

O-H bond. Among such properties a prominent one is the ultraviolet absorption spectrum and the theory may therefore be used for the examination of some of the spectroscopic shifts which accompany the lactam-lactim tautomerization. Much caution must, however, be exercised in this respect. Thus, in a recent paper Kwiatkowski135,137 performed Pariser-Parr-Pople-type calculations on the electronic structure of hydroxypurines, essentially to interpret their ultraviolet spectra. In these calculations he assumed that these compounds exist predominantly in their lactim form, and the results of his calculations, at least for 6- and 8-hydroxypurine, did not seem to contradict this assumption. It is only in the case of the 2-hydroxy isomer that a particularly striking disagreement between theory and experiment led him to admit that this last compound may exist in the lactam form. Calculations carried out for this form gave, in fact, a more satisfactory agreement with experiment.138 As we have seen, unambiguous infrared spectroscopy evidence clearly show s that all three isomers exist essentially in the lactam form. This shows that ultraviolet absorption may provide only very uncertain evidence about the lactam-lactim tautomerism in hydroxypurines and related compounds. 

An interesting series of degradation products has been reported recently by Muller et al. (356). In addition to allocolchicine and some recovered starting material, a desacetylthiocolchicine, CjoH23N04S, has been obtained from the action of sodium methyl mercaptide on methylthiocolchicide. This substance was optically active and showed an ultraviolet absorption spectrum that was different from that of methylthiocolchicide. The infrared spectrum showed carbonyl absorption at 5.93 fi. This was interpreted by the authors as indicative of a y-lactam, and desacetylthiocolchicine was assigned the tentative structure CXII. 

CF CN. Although the vacuum ultraviolet absorption spectrum of CF3CN (see Fig. 3.8.4) exhibits very little resolvable structure its major electronic features have been interpreted by comparison with those displayed by HCN in the same spectral region (see Fig. 3.8.3). On this basis, the weak difTuse banded absorption at 140 nm has been assigned to the intravalency o(7fl) - ir (3e) transition leading... 

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... 

Production of strand breaks by very low energy electrons (5-25 eV) in thin solid DNA films using ultrahigh vacuum systems have been reported in a number of studies [107-109]. Such studies have demonstrated the efficiencies of low energy electrons and photons to induce DNA damage. In the vacuum ultraviolet (UV) region, examination of experimental data [86,110,111] shows that the induction of strand breaks depends on the absorption spectrum of the components in the medium and the sensitivity spectrum of DNA [112]. Introduction of a variable with the wavelength for the induction of SSB by OH radicals, in conjunction with a fixed value for the quantum efficiency for the production of OH radical (sensitivity spectrum for induction of SSB in aqueous system [112]. 

TMB (42) was first generated by Roth el al. by photochemical decarbonyla-tion of the ketone 44 in a low-temperature matrix. This preparation was intensely colored, with a main transition at 490 nm and several subsidiary absorptions. Earlier ti-CI quantum chemical computations had predicted ultraviolet-visible (UV-vis) is transitions for the singlet and triplet states of TMB, and the bands observed by the Roth group were in better agreement with the predictions for the triplet. The preparation also showed a narrow ESR spectrum interpreted by the authors as that of a triplet species with D = 0.0042 cm and E = 0.0009 cm, which gave a linear Curie plot. The authors assumed that the carriers of the UV-vis and ESR spectra were the same species, namely, triplet TMB. They concluded that TMB is a ground-state triplet, contrary to the disjoint theory and to the computational results described above. 

In the second place, the spectrum of 3 Lyr is a very peculiar one, characterized not only by photospheric absorption lines but also by emissions that are strong in H, and are also present in He, and by other features, which arise partly in the gaseous stream from the B8 II component and partly in the outer edges of the opaque disk that surrounds and hides the so far unobservable companion. As it has been shown by Batten and Sahade (1973), in the case of H a, and by Aylin et al. (1987), in the case of the resonance lines of C IV, Si IV and N V in the IUE ultraviolet range, the line profiles can be interpreted in terms of a superposition of two profiles, one of them a broad, relatively faint emission that shifts back and forth throughout the orbital cycle. The behavior of the radial velocities from this feature suggests that it shares roughly the expected orbital motion of the companion to the B8 II component and, therefore, that it may arise in the optically thick disk that surrounds it. 

In later work, the absorption spectra of Bk(III) and Bk(IV) were recorded in various media (95). New absorption bands were reported as the result of using larger quantities of berkelium-249 of higher purity than had been previously available. Observations of the spectrum of Bk(III) were extended further into the ultraviolet wavelength region (to 200 nm), and nine new absorption bands were reported (96). Later the absorption spectra of Bk(III) and Bk(IV) in 2 M perchloric and 0.5 M nitric acid solutions have been obtained (97). An interpretation of the low-energy bands in the solution absorption spectra of Bk(III) and Bk(IV) has been published (98). 

Several spectroscopic investigations concerning pyridazine have been performed. Pyridazine is isoelectronie with benzene and replacement of CH groups in the latter by the more electronegative nitrogen atoms causes a marked dilferenee, alike with the other two diazines, in the near ultraviolet speetrum. It has a highly aromatic type of absorption spectrum. The ultraviolet spectra of pyridazine, its anion, and cation have been measured in different solvents, calculated, and interpreted. A detailed discussion... 

Ultraviolet spectrophotometry is considered a valuable tool as an aid for confirming the identification of pesticide residues. A correlation between the UV spectrum and the structure of several pesticides is discussed. Knowledge of such correlation may provide clues about the general type of chromophore present and may help the analyst to design analytical procedures. The transparency of many groups in the near UV imposes a limitation on interpretations of the absorption bands in this region. However, when taken in conjunction with the information obtained by IR, NMR, and mass spectroscopy, UV spectra may lead to structural proposals of value to the pesticide analyst. A discussion of the methods that have been utilized for the analysis of pesticides on the submicrogram level is also presented. 

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