Radicals electronic absorption

In a KI matrix the electronic absorption maximum of 82 - is observed at 400 nm, and the 88 stretching vibration by a Raman line at 594 cm k 83 shows a Raman line at 546 cm and an infrared absorption at 585 cm which were assigned to the symmetric and antisymmetric stretching vibrations, respectively. The bromides and iodides of Na, K, and Rb have also been used to trap 82 - but the wavenumbers of the 88 stretching vibration differ by as much as 18 cm- from the value in KI. The anion S3- has been trapped in the chlorides, bromides and iodides of Na, K, and Rb [120]. While the disulfide monoanion usually occupies a single anion vacancy [116, 122], the trisulfide radical anion prefers a trivacancy (one cation and two halide anions missing) [119]. 

The electronic absorption spectra of the products of one-electron electrochemical reduction of the iron(III) phenyl porphyrin complexes have characteristics of both iron(II) porphyrin and iron(III) porphyrin radical anion species, and an electronic structure involving both re.sonance forms Fe"(Por)Ph] and tFe "(Por—)Ph has been propo.sed. Chemical reduction of Fe(TPP)R to the iron(II) anion Fe(TPP)R) (R = Et or /7-Pr) was achieved using Li BHEt3 or K(BH(i-Bu)3 as the reductant in benzene/THF solution at room temperature in the dark. The resonances of the -propyl group in the F NMR spectrum of Fe(TPP)(rt-Pr) appear in the upfield positions (—0.5 to —6.0 ppm) expected for a diamagnetic porphyrin complex. This contrasts with the paramagnetic, 5 = 2 spin state observed... 

The technique of flash photolysis was originally developed by Norrish and Porter as a method for studying reactive species such as triplets and radicals with relatively short lifetimes (r > 1 x 10 6 sec).<6) The beauty of this technique is that it involves the direct observation of the species of interest. The principal problem, however, is to determine the identity of the species causing the new electronic absorption. For their efforts in the development of this technique Norrish and Porter, along with Eigen, received the Nobel Prize in chemistry in 1961. 

Shida, T. (1988). Electronic Absorption Spectra of Radical Ions. Elsevier, New York... 

The broad emission and low-fluorescence quantum yield of PPS suggested a distribution of trapping sites in the Si skeleton, which were also considered responsible for the lower-than-expected conductivity. The far-IR spectrum of PPS suggested the existence of cyclohexasilane rings connected by linear chains.361,362 Subsequent investigations by Irie et al. on the electronic absorption spectra of radical ions of poly(alkylsilyne)s were taken to indicate the presence of various cyclic silicon species, in corroboration of this conclusion.363 The large Stokes shift and broadness of the fluorescence emission indicate a range of fluorophore structures, different from the chromophore structures. This is... 

Shida, T. (1988). Electronic Absorption Spectra of Radical Ions. Elsevier, New York Shiner, Jr, V. J. (1970). In Isotopes Effects in Chemical Reactions (ed. Collin, C. J. 

Electronic Absorption Spectroscopy. Absorption spectra have been obtained for radical cations and anions generated from a number of carotenoids [phytoene (7,8,ll,12,7, 8, ll, 12 -octahydro-i//,i/ -carotene) (135) and canthaxanthin ()3,/3-carotene-4,4 -dione) (130)] and related polyenes [7,7 -dihydro- -carotene (131),... 

The electronic structures of polysilane radical ions have also been studied by pulse radiolysis of the liquid solution [35-40]. However, due to short lifetime of the radical ions, the measurement is limited to electronic absorption spectroscopy. 

Figure 21 Comparison of the electronic absorption spectra of poly(cyclohexylmethylsilane) and poly(methylphenylsilane) radical anions and cations at 77 K in -y-irradiated MTHF and freon matrices, respectively.

Figure 6.8. Electronic absorption spectra of the tetracene radical anion (a) and radical cation (b). [Adapted from Ref. 58.]...

Dicyclopentadiene forms a radical cation (20 ) in which one of the bonds linking the monomer units is cleaved. The species contains two allyl moieties attached to a C4 spacer . Structure 20 + rests on an unmistakable CIDNP pattem " and is supported by an analysis of the electronic absorption spectmm. The large energy gap in the OS of this ion (AE = 1.67 eV) is incompatible with the photoelectron spectrum of the parent molecule (AE = 0.15 eV), but it fits the ring-opened structure 20 +. 

Matrix-isolated alkali atoms (or small clusters) also undergo easy photoionization, and the electrons released in this process may attach themselves to nearby substrates to form the corresponding radical anions. However, one drawback of alkah metal atoms or clusters is that they tend to swamp the electronic absorption spectrum of the target reactive intermediate that can only thus be detected by IR. 

Picosecond electronic absorption spectroscopy was used to investigate the formation of the 9-methyl-9-fluorenyl radical following 266-nm, 18-ps pulsed excitation of the peroxyester in either cyclohexane or acetonitrile. The absorption of the 9-methylfluorenyl radical (3) grows with a rise time of 55 15 ps as monitored at a single, unreported wavelength. The proposed events following 266-nm, pulsed excitation is outlined in Scheme 19.1 in terms of a pathway in which the 0—0 bond is... 

Electronic absorption spectra of fc-benzenechromium (I) iodide (5) and its derivatives have been recorded and discussed by Yamada et al.26,26 They noted a loss of the benzene rings aromaticity in these compounds with the n electrons being drawn toward the metal and thereby conferring more a cyclopentadienyl radical character on the rings. 

We have investigated the reactions of the COs " radicals with double-stranded DNA by laser flash photolysis techniques [15]. In these time-re-solved experiments, the COs radicals were generated by one-electron oxidation of HCOs by sulfate radical anions, SO4 the latter were derived from the photodissociation of persulfate anions, S20s initiated by 308-nm XeCl excimer laser pulse excitation. In air-equilibrated buffer solution containing the self-complementary oligonucleotide duplex d(AACGCGAATTCGCGTT), 208 , and an excess of HCO3., the decay of the CO3 radical anion absorption band at 600 nm is associated with the concomitant formation of the characteristic narrow absorption band of the G(-H) radicals near 310 nm. 

T. Shida, Electronic absorption spectra of radical ions, Elsevier, Amsterdam, 1988, 239. 

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