Radical anion stability

DCB radical anions. Stabilities of the intermediates were estimated by calculated heats of formation. Employing these, the theoretical results were in good agreement with the experiment (Scheme 15) [21]. 

The halide radical anion stability has been calculated at the STO-3G level and found to have a low barrier to dissociation when solvated by water molecules16. In solution it cannot be observed (equation 1) because of the small barrier to its dissociation (ca 6 kcal... 

The absolute rate of dissociation of the radical anion of /i-nitrobenzyl chloride has been measured as 4 x 10 s . The w-nitro isomer does not undergo a corresponding reaction. This is because the meta nitro group provides no resonance stabilization of the benzylic radical. 

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... 

Nowadays, ultramarine-type pigments are produced synthetically. Inside the zeolite structure the highly reactive sulfur radical anions are well protected which explains the stability of the blue color over thousands of years in air. However, the species responsible for the blue color should not be confused with the sulfur radical cations responsible for the blue color of sulfur solutions in fuming sulfuric acid (oleum) and similar oxidizing mixtures... 

The electrophilic character of sulfur dioxide does not only enable addition to reactive nucleophiles, but also to electrons forming sulfur dioxide radical anions which possess the requirements of a captodative" stabilization (equation 83). This electron transfer occurs electrochemically or chemically under Leuckart-Wallach conditions (formic acid/tertiary amine - , by reduction of sulfur dioxide with l-benzyl-1,4-dihydronicotinamide or with Rongalite The radical anion behaves as an efficient nucleophile and affords the generation of sulfones with alkyl halides " and Michael-acceptor olefins (equations 84 and 85). 

The triphenylborane radical-anion itself has long been known to exist as a dimer (44),43 but the structure of Krause s dimer, as it has come to be known, has been elucidated only recently.44 A particularly stabilizing feature of 44, it turns out, involves B—C 7r-bonding, for the union of two units of 43 forms an orange solid whose H-NMR spectrum displays a telltale methine H at 4.03 ppm ( in 44 Eq. 13). 

The other mechanism, if in fact there is one, is perhaps via a radical anion as per the SET mechanism suggested by Heitz (14,15) for other polymerizations. The ability of the long silicon chain to delocalize electrons would assist in stabilizing either radical anions or straight anionic species. A simple radical is preferred by Zeigler (9) for the formation of the highest MW fraction in the polymerization of PMDS, a product for whose route no evidence has accrued In this work. 

Supersilyl substituents also stabilize negative charges extremely well In the radical anion of 1,4-di(tris(trimethylsilyl)silyl)benzene - as proven by ESR/ENDOR coupling constants [5a,c] augmented by HMO estimates for the "blind" centers (2 O) [5a,c] - more than half of the it spin population p is located in its Si(SiR3)3 groups. 

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