Carbonate species radical anions

In the example shown in Eig. 2.11 [29] the paramagnetic species is the carbon dioxide radical anion, CO2, in an X-irradiated lithium formate crystal. ENDOR lines from several Li nuclei (/ = 3/2) at different lattice positions occur. The principal values and directions of the hyperfine coupling tensors provide a means to obtain the geometric arrangement of the ions about CO2. The analysis is based on the point dipolar approximation, in which the maximum value, bmax, in MHz of the dipolar coupling is given by... 

Approximate axial g-tensors are frequently observed for transition metal ion complexes. Inorganic radicals can also have appreciable axial g-anisotropy. This property is of value for the assignment of ESR powder spectra in applied studies. Carbon dioxide radical anions, CO2, and related species contribute for instance to the ESR signal used for geological dating [21] see Chapter 9. The ESR spectrum of this anion has also been employed as an indicator that a certain foodstuff has been irradiated, for dosimetric purposes in certain carboxylic acid salts, and as a component in tooth enamel samples used in retrospective dosimetry. 

Oxygen-centered radicals are arguably the most common of initiator-derived species generated during initiation of polymerization and many studies have dealt with these species. The class includes alkoxy, hydroxy and aeyloxy radicals and tire sulfate radical anion (formed as primary radicals by homolysis of peroxides or hyponitrites) and alkylperoxy radicals (produced by the interaction of carbon-centered radicals with molecular oxygen or by the induced decomposition of hydroperoxides). 

Monomers, such as ethylene, propylene, isobutylene, and isoprene, containing the carbon-carbon double bond undergo chain polymerization. Polymerization is initiated by radical, anionic or cationic catalysts (initiators) depending on the monomer. Polymerization involves addition of the initiating species R, whether a radical, cation, or anion, to the double bond followed by its propagation by subsequent additions of monomer... 

XOR is a cytoplasmic enzyme and a ready source of electrons for transfer to molecular oxygen to form reactive oxygen species such as superoxide and peroxide. It is therefore thought to be involved in free radical-generated tissue injury and has been implicated in the pathogenesis of ischemia-reperfusion damage. Moreover, it has recently been implicated in the production of peroxynitrite (89), and carbonate radical anion (92), both potent biological oxidants. Its exact role in lipid peroxidation, inflammation, and infection needs... 

Experimental data (Figure 4.2) for the dissociative electron transfer between radical anions and the carbon-halogen bond in alkyl halides indicates a linear relationship between log(k ) and Ed over a wide range of reaction rates [5, 9]. Very fast reactions become controlled by the rate of diffusion of two species towards each other, when every close encounter gives rise to electron transfer. A parabolic... 

At low pH values, dimerization must involve the combination of two neutral carbon radicals since the same ( ) / meso ratio is obtained as from the photochemical reaction of the carbonyl compound in methanol [26], a process which also involves neutral radicals. The switch in isomer ratio to that characteristic of alkaline media occurs in the region of pH close to the value of pKj for the neutral radical. Dimerization then occurs in a fast reaction between the radical-anion and the neutral radical. In strongly alkaline solutions where the pH pK the major reactive species formed at the potential of the first reduction wave is the radical-anion. Reaction between two radical-anions is relatively slow due to coulorobic repulsion so that dimerization in strongly alkaline solution still occurs by reaction... 

Radical additions to alkenes and aromatic systems are well known reactions. The trapping in this manner of radicals obtained by reduction of the aliphatic carbonyl function has proved to be a versatile electrochemical route for the formation of carbon-carbon bonds. Such reactions are most frequently carried out in protic solvents so that the reactive species is a o-radical formed by protonation of the carbonyl radical-anion. Tlie cyclization step must be fast in order to compete with further reduction of the radical to a carbanion at the electrode surface followed by protonation. Cyclization can be favoured and further reduction disfavoured by a... 

The radical-anions of aliphatic nitrocompounds are detectable in aqueous solution as transient intermediates formed during continuous electrolysis in the cavity of the esr spectrometer [4], Decay of the species occurs by protonation and then further reactions. 2-Methyl-2-nitropropane has no acidic hydrogens so that it can be examined in aqueous alkaline solution where the radical-anion is not protonated. Over the pH range 9-11, this radical-anion decays by a first order process with k = 0.8 0.1 s at 26 C. Decay results from cleavage of the carbon-nitrogen bond to give a carbon centred radical and nitrite ion. Ultimately, the di-(ferr,-butyI)nitrone radical is formed in follow-up reactions [5],... 

The formation of RSSR from RS and RS species is particularly relevant in the present context because it is the reverse of the electro-induced radical anion cleavage (equation 76). Actually, the formation of RSSR from reaction (79) is as well studied as the reaction between aryl carbon radicals and anionic nucleophiles, the fundamental step of the SrnI. Equilibrium constants in the range 10 -10 M for reaction (79) were determined for a number of alkyl-type systems in water, although the corresponding values for aryl-type systems are smaller. The rate constants... 

In many of our later discussions of organic reactions, we will be concerned with cationic, radical, and anionic carbon species that are substitution products of CH3 , CH3-, and CH3 Q. Because of the importance of these entities, you should know how to formulate them and related substances, such as G NH2, with atomic orbitals. Perhaps the most straightforward way is to start from CH4 and see what changes in the C-H bonds we would expect as the result of the hypothetical processes CH4 —> CH3 e + H , CH4 — CH3 + H , and CH4 — CH3- + H-. 

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