Aromatic anions, solvated electron formation from

The results for phenolate and naphtholate show that internal transition may lead to solvated electron formation from aromatic anions. The fact that the products are the negatively charged solvated electron and a radical which is neutral (and not a positively charged one) may be partly responsible for the increased efficiency of anions over the undissociated molecules. Primary recombination may decrease in the absence of coulombic attraction. Moreover the ionization potential of the anion is lower. 

In general, from among the protic solvents, only liquid ammonia (the first used)1 is particularly useful, and is still used more than any other solvent despite the low temperature at which reactions have to be carried out (b.p. -33 °C) and the fact that solubilities of some aromatic substrates and salts (M+Nu-) are poor. Ammonia has the added advantage of being easily purified by distillation, being an ideal system for production of solvated electrons, and has very low reactivity with basic nucleophiles and radical anions, and aryl radicals. Also, poor solubilities can sometimes be ameliorated by use of cosolvents such as THF. In addition it can be used as a solvent for the in situ reductive generation of nucleophiles such as ArSe- and ArTe- ions, e.g. the formation of PhTe- from diphenyl ditelluride (equation 16).54 55... 

Alkali and alkaline earth metals dissolve in liquid ammonia with the formation of solvated electrons. These solvated electrons constitute a very powerful reducing agent and permit reduction of numerous conjugated multiple-bond systems. The technique, named for Birch provides selective access to 1,4-cydohcxiidicnes from substituted aromatics.8 In the case of structures like 21 that are substituted with electron-donating groups, electron transfer produces a radical anion (here 22) such that subsequent protonation occurs se lectively in the ortho position (cf intermediate 23) A second electron-transfer step followed by another protonation leads to com pound 24... 

In the S l mechanism of aromatic substitution the initiating step is the formation of a radical anion. In order to distinguish the process from the route described above (SR+N1) in which a radical cation plays a crucial role, the symbol S l has been used17. Creation of the radical anion can occur by several procedures. The reaction can be electrochemically initiated, a solvated electron in a solution of alkali metal in liquid ammonia may be involved or a radical anion may be used as the source of electrons. The most common source of electrons is, however, the nucleophile itself involved in the substitution reaction. In many cases the electron transfer from nucleophile to substrate is light-catalysed and the process is then sometimes referred to as S l Ar. Although the nucleofugic group in S l... 

In polar solvents, such as acetonitrile, organic donor-acceptor systems such as those listed in Table 6.2 show only the fluorescence due to A no new fluorescence appears as in exciplex formation. Flash spectroscopy shows absorption spectra characteristic of the hydrocarbon radical anion and the amine radical cation. The product in these solvents is either an ion-pair or two free ions, stabilised no doubt by solvation, and the reaction is a complete transfer of an electron from one molecule to another, rather than exciplex formation. The reaction goes effectively to completion, and so (with only one fluorescence lifetime to be considered) the kinetic equations for the intensity and lifetime reduce to the simple Stem-Volmer forms (Equations (6.16) and (6.19)). The rate constants for the reactions of aromatic hydrocarbons with various amines in acetonitrile are found to be correlated with the free-... 

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