Electron capture dissociative

Furlei and coworkers44 studied the negative ion mass spectra of several cyclic sulfones (82-98) upon dissociative electron capture and concluded that the negative molecular ions were notably stabilized by the introduction of electron-withdrawing substituents and/or unsaturation. Some difference was found in the negative ion mass spectra of configurational isomers (85 vs. 86 and 87 vs. 88) in contrast to the situation in their positive ion spectra. A strong S02 ion (m/z 64) was observed also for all the compounds studied. 

In pulse radiolysis studies, sulfonyl radicals have normally been generated by dissociative electron capture using sulfonyl chlorides as substrates, namely15. 

In reactions [5]-[8] pure electron addition occurs, but in reaction [9] addition and dissociative electron capture giving loss of MeO occur concurrently. Furthermore, CH3 radicals are also formed, together, presumably, with (Me0)2P02 this being an alternative dissociative route. Reaction [10] occurs in methanol, there being no clear sign of the parent anion, P(0Me)3 . This protonation step is also accompanied by dissociative electron capture to give P(0Me)2 radicals. 

In the absence of 13C hyperfine interaction measurements, it is not clear to what extent dissociative electron capture with CO loss occurs for such molecules. It is entirely possible, for example, that electron capture by M(CO)sI results in loss of the axial CO ligand, yielding the radical M(C0)4I2-. If so, it is noteworthy that CO is lost in preference to I-. 

HC1 is formed by a chain mechanism with a very high yield (M /N value —103), presumably because of the high reactivity of the Cl atom. The chain is initiated by the production of H and Cl atoms. Dissociative electron capture by Cl2 requires about 1.6 eV energy. Therefore, presumably both kinds of ions are initially produced by excitation and ionization. The chain is propagated simply as follows ... 

The irradiation of alkyl vinyl ethers leads to dissociative electron capture. Yoshida et al. (1972) showed that dimethyl ether decomposes according to... 

Macroradicals are readily formed in solution by dissociative electron capture... 

The second result relates to an electronation procedure in which field emission into liquids provides a source of low energy electrons which are capable of effecting selective chemical changes (Noda et al., 1979). Thus dissociative electron capture by alkyl halides, and electron capture followed by protonation, afford alternative routes to specific spin adducts, as exemplified in Scheme 8. 

Resonance electron capture directly yields the negative molecular ion, M"", whereas even-electron fragment ions are formed by dissociative electron capture and ion-pair formation. Molecular ions are generated by capture of electrons with 0-2 eV kinetic energy, whereas fragment ions are generated by capture of electrons from 0 to 15 eV. Ion-pair formation tends to occur when electron energies exceed 10 eV. [77]... 

Fig. 7.11. Energetics of (a) resonance electron capture, (b) dissociative electron capture, and (c) ion-pair formation. Adapted from Ref. [75] by permission. John Wiley Sons, 1981.

According to ESR spectra, cyclobutanone and tetramethylene sulfone undergo dissociative electron capture process (Scheme 3.34 for cyclobutanone) in argon matrices and yield distonic anion-radicals (Kasai 1991, Koeppe and Kasai 1994). 

Primary electron energy dissociative electron capture results from low-energy secondary electrons released from a metal surface. 

Interactions of C02 with alkyl halogenides or with compounds containing halogen-nitrogen bonds take place as dissociative electron captures. As a result, free radicals are formed according to Scheme 1-88 ... 

The hydrated electron reacts with many compounds which are capable of releasing an anion by dissociative electron capture [e.g., reaction (8)], and, among others, it was this property which allowed the differentiation between eaq and H" [reactions (9) and (10)] (Armstrong et al. 1958 Hayon and Allen 1961 Jortner and Rabani 1962). 

The DNA backbone could be split, in principle, by dissociative electron capture [reactions (19)-(21)]. 

The allylic radical has also by abstraction of the allylic hydrogen by the H2NC(0)CH2 radical in Thd [reaction (210] and its isomer has been produced from 6-chloromethyluracil by dissociative electron capture and also in low-tem-... 

Some scientists emphasized that the degradation of TBP was due to dissociative electron capture via the following reaction (279, 283, 285, 286) ... 

With pulse radiolysis and flash photolysis, Jin et al. have recently focused on the examination of TBP excited species (291). The authors concluded that the decomposition of TBP occurred through two processes dissociative electron capture (Equation 8.1) and decomposition of TBP excited molecules (Equation 8.2). 

According to Kerr and Webster (279), the radiolysis of TBP leads to alkyl radicals R and OP(OR)2OR . Investigations of the radical intermediates, by ESR examination or by use of electron scavengers, provided clear evidence regarding the formation of R radicals by dissociative electron capture (Equation 8.1) (294). 

Kerr, C.M.L., Webster, K., Williams, F. 1972. Electron spin resonance evidence for dissociative electron capture in y-irradiated phosphate esters. J. Phys. Chem. 76(20) 2848-2850. 

Chloroaliphatic compounds have been shown to undergo quantitative dechlorination on reaction with e-q (Hayon and Allen, 1961 Stockdale and Sangster, 1966). Bromo- and iodo-derivatives follow a similar pattern (Anbar, 1965 Anbar and Neta, 1967c). This dehalogenation is not a result of a dissociative electron capture... 

The formation of C5H5Co was observed at low ionizing energy, and is probably formed by a dissociative electron capture process. 

Bernhard and co-workers have performed a series of experiments to determine the mechanisms of DNA strand breakage by direct ionization of plasmid DNA. A big surprise in this work was the discovery that the total yield of single strand breaks exceeds the yield of trapped sugar radicals. Even at very low hydration levels (2.5 waters per nucleotide residue) nearly 2/3 of the strand breaks are derived from precursors other than deoxyribose radicals [74], The authors conclude that a majority of the strand breaks observed do not result from dissociative electron capture, homolytic bond cleavage from excited states, or from hydroxyl radical attack. Rather, the authors conclude that doubly oxidized deoxyribose is responsible for the high yield of strand breaks. 

Capture may take place to bound states of the negative ion that undergo radiationless transitions to repulsive states of the negative ion resulting in dissociative electron capture. These radiationless intramolecular transitions (Auger transitions) are a result of overlap of the discrete states with a continuum of states of AB-. These types of processes are illustrated for diatomic molecules in Figure 2.2b. Electrons are first captured into the bound state represented by curve 1, and before autodetachment can take place an intramolecular radiationless transition occurs to curve 2 resulting in dissociation into A and B-. 

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