Substituted radical anions

The radical anion of /3-trimethylsilylstyrene also undergoes dimerization but coupling takes place at the carbons a to silicon 33). The kinetics of the alkyne dimerization, followed by ESR, showed the reaction to be second order in radical anion 43). With Li+, Na+, K+, or Rb+ as the counterions, the rate increases in the order Si < C < Ge 45). Consistent with the increased stability of the trimethylsilyl-substituted radical anion, the radical anion of 1,4-bis(trimethylsilyl)butadiyne, produced by reduction with Li, Na, K, Rb, or Cs in THF is stable at room temperature even on exposure to air, whereas the carbon analog, 1,4-di-r-butyl-1,3-butadiyne radical anion, dimerizes by second-order kinetics at -40° (42). The enhanced stability of the trimethylsilylalkynyl radical anions has been attributed to p-drr interactions (42). 

Dessy etal. 5 9 generated the mercury substituted radical anion of nitrobenzene for ESR observation by reduction of bis (p-nitrophenyl)mercury. The aj jg coupling constant was found to be 10 times larger than the corresponding tzH coupling constant, an amplification which is useful for the resolution of small ay coupling constants by substitution of H versus Hg. 

Electron transfer between oxygen and nitro-substituted radical anions H20 (22 0.2)... 

Sigmatropic rearrangement of deuterium-labeled bicyclo[3.1.0]hexenyl radicals occur below — 60°C (equation 31) and are faster than ring-opening Lifetimes for ringopening of some cyclopropyl-substituted radical anions (156) have been studied, as well as the ESR spectra of p-cyclopropylnitrobenzene radical anion (157). ... 

Fig. 15. Electronic spectra of aromatic nitro-substituted radical anions and results of the semiempirical calculations (taken from Shida, T., Iwata, S., Ref. lO ))...

Section 15.2 contains hydrocarbon and substituted hydrocarbon anion radicals. It is divided into two main parts Section 15.2.1 deals with hydrocarbon radical anions whilst Sect. 15.2.2 deals with substituted compounds and is subdivided into 3 subsections. Section 15.2.2.1 is concerned with the substituted radical anions, Sect. 15.2.2.2 deals with perfluoro and perchloro substituted radical anions, and Sect. 15.2.2.3 contains substituted fluorenones. These have been included for completeness and because we feel that they may not be included elsewhere. Mono-, di- and trianions are also included. 

Also ESR study of corresp. 2,5-dimethylphenyl substituted radical anions. 

Ammonium Compounds. Salts and hydroxides containing quadricovalent nitrogen are named as a substituted ammonium salt or hydroxide. The names of the substituting radicals precede the word ammonium, and then the name of the anion is added as a separate word. For example, (CH3)4N+I is tetramethylammonium iodide. 

The neat resin preparation for PPS is quite compHcated, despite the fact that the overall polymerization reaction appears to be simple. Several commercial PPS polymerization processes that feature some steps in common have been described (1,2). At least three different mechanisms have been pubUshed in an attempt to describe the basic reaction of a sodium sulfide equivalent and -dichlorobenzene these are S Ar (13,16,19), radical cation (20,21), and Buimett s (22) Sj l radical anion (23—25) mechanisms. The benzyne mechanism was ruled out (16) based on the observation that the para-substitution pattern of the monomer, -dichlorobenzene, is retained in the repeating unit of the polymer. Demonstration that the step-growth polymerization of sodium sulfide and /)-dichlorohenzene proceeds via the S Ar mechanism is fairly recent (1991) (26). Eurther complexity in the polymerization is the incorporation of comonomers that alter the polymer stmcture, thereby modifying the properties of the polymer. Additionally, post-polymerization treatments can be utilized, which modify the properties of the polymer. Preparation of the neat resin is an area of significant latitude and extreme importance for the end user. 

Electrochemical reduction of pentatluoronitrobenzene produces an intermediate radical anion that couples at position 4 to form the corresponding biphenyl along with hydroxy derivatives from subsequent nucleophilic substitution meta to the nitio groups [44] (equation 34) Similar reduction of halopyridines such as pen-tafluoropyridine leads mainly to 4,4 bipyridyls [45] (equation 35)... 

Addition polymerization is employed primarily with substituted or unsuhstituted olefins and conjugated diolefins. Addition polymerization initiators are free radicals, anions, cations, and coordination compounds. In addition polymerization, a chain grows simply hy adding monomer molecules to a propagating chain. The first step is to add a free radical, a cationic or an anionic initiator (I ) to the monomer. For example, in ethylene polymerization (with a special catalyst), the chain grows hy attaching the ethylene units one after another until the polymer terminates. This type of addition produces a linear polymer ... 

Kattenberg and coworkers54 studied the chlorination of a-lithiated sulfones with hexachloroethane. These compounds may react as nucleophiles in a nucleophilic substitution on halogen (path a, Scheme 5) or in an electron transfer reaction (path b, Scheme 5) leading to the radical anions. The absence of proof for radical intermediates (in particular, no sulfone dimers detected) is interpreted by these authors in favour of a SN substitution on X. 

Novi and coworkers124 have shown that the reaction of 2,3-bis(phenylsulfonyl)-l,4-dimethylbenzene with sodium benzenethiolate in dimethyl sulfoxide yields a mixture of substitution, cyclization and reduction products when subjected at room temperature to photostimulation by a sunlamp. These authors proposed a double chain mechanism (Scheme 17) to explain the observed products. This mechanism is supported by a set of carefully designed experiments125. The addition of PhSH, a good hydrogen atom donor, increases the percent of reduction products. When the substitution process can effectively compete with the two other processes, the increase in the relative yield of substitution (e.g., with five molar equivalents of benzenethiolate) parallels the decrease in those of both cyclization and reduction products. This suggests a common intermediate leading to the three different products. This intermediate could either be the radical anion formed by electron transfer to 2,3-bis(phenylsulfonyl)-l,4-dimethylbenzene or the a radical formed... 

Bowman and Symons145 probed the stability of a series of radical anions involved in the SRN1 substitution for a-substituted aliphatic nitro-compounds [Me2C(X)N02] by studying with ESR at 77 K the succession of events following electron capture by Me2C(X)N02. The radical anions were more concentrated in an ether matrix than in an... 

First reported by Fredenhagen in 1926 F3, F4), the graphite-alkali-metal compounds possess a relative simplicity with respect to other intercalation compounds. To the physicist, their uncomplicated structure and well defined stoichiometry permit reasonable band-structure calculations to be made S2,12) to the chemist, their identity as solid, "infinite radical-anions frequently allows their useful chemical substitution for such homogeneous, molecular-basis reductants as alkali metal-amines and aromatic radical anions N2, B5). 

In certain reactions where nucleophilic substitutions would seem obviously indicated, there is evidence that radicals and/or radical ions are actually involved. The first step in such a process is transfer of an electron from the nucleophile to the substrate to form a radical anion ... 

Some of the reactions in this chapter operate by still other mechanisms, among them an addition-elimination mechanism (see 13-15). A new mechanism has been reported in aromatic chemistry, a reductively activated polar nucleophilic aromatic substitution. The reaction of phenoxide with p-dinitrobenzene in DMF shows radical features that cannot be attributed to a radical anion, and it is not Srn2. The new designation was proposed to account for these results. 

HMO Predictions for Dimerization Equilibria of Substituted Ethylene Radical Anions ... 

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