Electron expulsion

Radiation-induced electron transfer to nitroso compounds has also been studied. This technique, using electron expulsion from trichlorofluoromethane, provided data that the radical cation 54 is formed from nitrosobenzene at 77 K. Analysis of the EPR spectrum indicates that the singly occupied MO lies in the plane of the benzene ring and has high 2s character74. Irradiation of the dimer 55 under the same conditions shows that a trace of the monomeric radical cation 56 is produced74. 

Aminolysis of esters often reveals general base catalysis and, in particular, a contribution to the reaction rate fi om terms that are second-order in the amine. The general base is believed to function by deprotonating the zwitterionic tetrahedral intermediate. Deprotonation of the nitrogen facilitates breakdown of the tetrahedral intermediate, since the increased electron density at nitrogen favors expulsion of an anion ... 

The acetoxy dienone (218) gives phenol (220). Here, an alternative primary photoreaction competes effectively with the dienone 1,5-bonding expulsion of the lOjS-acetoxy substituent and hydrogen uptake from the solvent (dioxane). In the case of the hydroxy analog (219) the two paths are balanced and products from both processes, phenol (220) and diketone (222), are isolated. In the formation of the spiro compound (222) rupture of the 1,10-bond in the dipolar intermediate (221) predominates over the normal electron transmission in aprotic solvents from the enolate moiety via the three-membered ring to the electron-deficient carbon. While in protic solvents and in 10-methyl compounds this process is inhibited by the protonation of the enolate system in the dipolar intermediate [cf. (202), (203)], proton elimination from the tertiary hydroxy group in (221) could reverse the efficiencies of the two oxygens as electron sources. 

Both cis- and rrans-l-arylsulfonyl-2-arylsulfenyl propenes (56) underwent a Smiles rearrangement under electron impact at 20 and 70 eV and formed a diarylsulfide ion [M — 104]+ (equation 27a)39 through a process where a bond between the R C H group and the sulfide sulfur is formed and a rearomatization occurs by a loss of the neutral thiirene dioxide or a simultaneous expulsion of SOz and propyne. The ion m/z 148 was also obtained from all of the sulfonyl-sulfides, 56 (equation 27b) and here the loss of R2 seemed to be related to the bond strength39. In addition to the above compounds 56 exhibited some simple cleavages before and after sulfone-sulfinate rearrangements. 

In the first mechanism (equation 74) the nucleophile function attacks the aromatic ring in an ipso-type displacement involving a Meisenheimer complex intermediate243,244, and leads to the rearranged product after expulsion of sulfinate anion (X-). This mechanism should be favoured by the presence of an electron-withdrawing substituent in conjugation with the anion. The second mechanism (equation 75) involves a direct displacement of sulfinate anion (X ) by Y-, without involvement of the aromatic n electrons. 

Absorption of one photon of light results in the relocation (with respect to space, spin or both) of one electron. It is possible, but extremely unlikely, that a second photon, together with its associated electronic rearrangement, can be absorbed before the ground state is reacquired upon expulsion of a photon. It s unlikelyhood is because the lifetime of the excited state is typically only 10 seconds or so. 

A further complicating factor is that many low-energy y-transitions are converted, that is, their energy is released through the expulsion of one or more atomic electrons. This gives rise to the Auger cascade, which will be described below. 

A significant number of Ir111 complexes arise from the oxidative addition reactions of Ir1 species. Such reactions may proceed via routine addition, whereas some proceed by ligand expulsion in conjunction with oxidative addition. Complexes containing Ir111 have a low-spin d6 electronic configuration, and are usually to be found with an octahedral-based ligand set. 

One way of stabihzing the initial radical or anion radical is therefore the addition of an acid. Expulsion of a base should produce a similar effect. This is indeed the case (Scheme 2.21), and the secondary radical thus formed is similarly easier to reduce than the starting molecule in most cases. RX is a molecule containing a low-lying orbital able to accommodate the incoming electron, thus leading to the primary radical, RX -, before the nucleophile X- is expelled. We consider here the case of a stepwise process in which the reaction pathway involves the intermediacy of the primary radical rather than a... 

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