Free radicals, absorption spectra

Upon photolysis of polypropylene hydroperoxide (PP—OOH) a major absorption at 1726 and 1718 cm has been observed in the IR spectrum, which is attributed to the carbonyl groups. Sometimes the macroradical having free radical site reacts with a neighboring newly born hydroperoxide causing the formation of a macroalkoxy radical [116]. 

Radiation chemical studies were carried out with an acidic WO3 H O sol stabilized by polyvinyl alcohol It was found that (CH3)2COH radicals inject electrons into the colloidal particles. A long-lived blue color arose and the absorption spectrum showed a rising absorption above 700 nm. This absorption could have been produced by free electrons, although it could not be ruled out that the electrons reduced ions... 

This polymeric lipid can first be polymerized by free radical initiator in organic solutions before making the vesicles. The proton NMR spectrum of the polymerized lipid shows that vinyl protons of the cyclic acrylate between 85.00 ppm and 86.00 ppm disappeared from the spectrum, compared with that of monomeric lipid. Also in the IR spectrum (Figure 6) the absorption peak at 1670 cm"1 for the cyclic acrylate carbon carbon double bond disappeared as the result of polymerization. The carbonyl absorptions of the esters at 1740 cm 1 and the lactone at 1805 cm"1 still remain in the spectrum. 

The chemically induced dynamic nuclear polarization (DNP) opened perspective to study products formed from free radicals [102], The basis of this study is the difference in NMR spectra of normal molecules and those formed from free radicals and radical pairs. The molecules formed from radicals have an abnormal NMR spectrum with lines of emission and abnormal absorption [102]. DNP spectra help to obtain the following mechanistic information ... 

Methods of electron spectroscopy are widely used to follow the electron-transfer process. Thus, the progress of electron transfer from naphthalene anion-radical to cup-stacked carbon nanotubes is easily detected by monitoring the UV absorption spectrum. Namely, the absorption band around 500-900 nm due to naphthalene anion-radical completely disappears after reduction of the nanotubes. At the same time, the reduced nanotubes exhibit ESR spectrum characterized with g-factor of 2.0025 (Saito et al. 2006). This g-value is close to the free spin g-factor of 2.0023 that is diagnostic of the delocalized electron on carbon nanomaterials (Stinchcombe et al. 1993). It should be parallelly... 

PCP-phenolic radical that possesses an absorption spectrum in H2O at 440 nm and decays via second-order kineties with k = 9. x 10 /M/s, as evidenced by pulse radiolytie studies. The PCP-phenolic radical can attach covalently to the C8-site of dG to generate the C8-OPCP adductIn the presence of GSH, redox cyeling of the phenoxyl radieal with thiyl radieal generation will yield a GSH disulfide anion radieal that ean reduetively aetivate O2 to generate the superoxide radieal anion (02 ) that ean generate free ferrous iron Free Fe " " may... 

A UVV spectrophotometric method for the specific detection of peroxycarboxylic acids in the presence of H2O2 is based on direct oxidation of ABTS (103) by the analyte in an acidic medium. The spectrum of the resulting green free radical presents five absorption maxima where measurements can be made 406, 415 (the most intense), 649, 732 and 815 nm. Full color development may be accelerated by traces of iodide. The LOD is 1 p,M of AcOOH, with linearity in the 2.5 to 100 p,M range. Note that reaction of 103 with H2O2 in Section in.B.2.a requires peroxidase catalysis. 

Figures 4.26, 4.27, and 4.28 show typical UV absorption spectra for some simple aldehydes and ketones (Rogers, 1990 Martinez et al., 1992 see also Cronin and Zhu, 1998, for n-pentanal). Formaldehyde stands out from the higher aldehydes and ketones in that it has a highly structured spectrum and furthermore, the absorption extends out to longer wavelengths. The latter difference is particularly important because the solar intensity increases rapidly with wavelength here (Chapter 3.C.1) and hence the photolysis rate constant for HCHO and the rate of production of free radicals...

Up to now we have been able to observe 13 separate absorption bands in the ultraviolet region of the spectrum between 220 and 400 m/. The shift in the Amax of polyenyl free radicals to longer wavelengths with increasing n would be expected to be linear with n, similar to the... 

Air Oxidation of Free Radicals. Curve 4 of Figure 2 represents the absorption spectrum after admitting air to the ultraviolet absorption cell. The bands at 258, 285, and 323 mp which we believe to be caused by the allyl, dienyl, and trienyl free radicals, respectively, were completely eliminated by the oxidation. 

The absorption spectrum observed in the pulse radiolysis of solid films of polystyrene is shown in Figure 5. The absorption spectrum around 540 nm is also very similar to the absorption spectrum of polystyrene excimer observed in irradiated polystyrene solutions in cyclohexane as reported previously (2,3). The absorption with the maximum at 410 nm was reported previously and was assigned to anionic species (13,14). The longer life absorptions, attributed to triplet excited polystyrene repeat units and nonidentifiable free radicals, were observed in a wave length region < 400 nm. The absorption spectrum of CMS films obtained in pulse radiolysis showed a peak around 320 nm and a very broad absorption around 500 nm as shown in Figure 6. 

The absorption band around 520 nm is very similar to that of polystyrene excimer (2,3,5). The decay follows first order kinetics with a lifetime of 20 ns. The decay rate agrees with that of the excimer fluorescence and excimer absorption. The longer life absorptions, attributed to the triplet states and free radicals (2,5), were observed at wave lengths <400 nm, although the anionic species of polystyrene with the absorption maximum at 410 nm as seen in solid films (cf. Figure 5) was not observed. Figure 9 shows the absorption spectrum observed in the pulse radiolysis of CMS solution in cyclohexane. 

The absorptions at both 500 nm and 320 nm follow first order kinetics with a lifetime of 420 ns. This absorption species is neither the excimer of polystyrene nor free cationic species of polystyrene. Although the excimer of polystyrene has an absorption band around 500 nm, the lifetime is only 20 ns. Further the free cationic species of polystyrene should live for a longer time in this solution, and the absorption band should exist in a longer wavelength region (6). These considerations of lifetime and absorption spectrum lead us to conclude that the absorption spectrum shown in Figure 12 is due to the charge transfer-radical complex between polystyrene and Cl radical (2,4,17). A very similar... 

The flame is a complex medium in dynamic equilibrium that must be perfectly controlled. It is characterised by its chemical reactivity for a given maximum temperature (Table 14.2) and by its spectrum. Free radicals present in the flame have an emission and absorption spectrum in the near UV and this can sometimes interfere with the measurement of some elements. Thus, the observation height of the flame must be adjusted for some elements. 

It is only very recently that attempts to obtain infrared spectra of free radicals have been successful.2 As these infrared studies are further developed, they promise to fill many of the gaps left by ultraviolet investigations, both with regard to radicals studied (since all radicals must have a discrete infrared spectrum), and with regard to the fundamental frequencies of the ground state, which in most cases are difficult to obtain from ultraviolet absorption spectra. 

Comparison of emission spectra between 2100 A and 6500A has shown only small differences in relative concns of excited species between low-pressure diffusion flames and explns, whereas during explns peak intensities may be as much as 100 times greater. The time dependence of the free-radical emission during expln indicates the formation sequence to be OH, CH, C2, and evidence for the forbidden CO Cameron bands has been obtained. Similarly the ultraviolet absorption spectrum of the OH radical in acetylene— H2—02 detonations has been measured in conjunction with the associated rarefaction waves (Ref 7). Analysis of the absorption spectrum has indicated average rotational temps greater than 3000°K during the initial 310 microseconds... 

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