Radical ion reactivity—I

Eberson, Lennart; Blum, Zoltan; Helgee, Bertil; Nyberg, Klas

doi:10.1016/0040-4020(78)88112-5

Cited by 51 publications

(16 citation statements)

References 67 publications

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“…Finally, in light of a recent interpretation of aromatic nitration provided by P e r r i r~,~~ one might consider a mechanism involving intermediacy of a radical cation, followed by recombination of the ion pair: (6) However, in contrast with the analogous process promoted by nitronium ion, reaction 6 would be energetically unfavorable. Furthermore, it has been long established that F-fails to undergo nucleophilic attack on aromatic radical a result recently rationalized by a theoretical interpretation offered by Eberson et aL6 In conclusion, it appears that all the radical reaction pathways encounter major difficulties in being consistent with the experimental features of the ring-substitution process promoted by molecular fluorine.…”

Section: Discussionmentioning

confidence: 98%

Substrate selectivity and orientation in aromatic Substitution by molecular fluorine

Cacace¹,

Giacomello²,

Wolf³

1980

J. Am. Chem. Soc.

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Direct elemental fluorination of representative aromatic substrates, including PhH, PhCH3, PhF, PhCI, PhBr, PhN02, PhCN, and PhOCH3, has been investigated in inert solvents, e.g., CC13F and other fluorocarbons, over the temperature range - 154 to 40 OC. In order to achieve the necessary control of the extremely reactive electrophile, and to minimize unwanted modifications of the reaction environment, the fluorination has been carried out at extremely low rates and correspondingly low conversions, generally below 0.01%, using as a reagent gaseous mixtures of F2 highly diluted ( < I mol %) in N2 or Ar. The partial rate factors, calculated from a consistent set of relative reactivity and orientation data measured at -78 OC in CC13F, correlate smoothly with the u+ constants for all the substituents investigated, giving a p+ value of -2.45 for aromatic substitution by elemental fluorine with a correlation coefficient of 0.993. These results characterize F2 as a highly reactive, and correspondently unselective, reagent, and support a polar electrophilic substitution mechanism that is discussed and compared with other plausible fluorination pathways

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Section: Discussionmentioning

confidence: 98%

Substrate selectivity and orientation in aromatic Substitution by molecular fluorine

Cacace¹,

Giacomello²,

Wolf³

1980

J. Am. Chem. Soc.

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“…In each case, the majority of halogen comes from the oxidant, not from the acid in workup, which is in some agreement with literature results involving the perylene radical cation. 35 The prior work, based on Dewar-Zimmerman indicated that halide ions belong to a class of reagents which do not react nucleophilically with perylene radical cation, but instead undergo electron transfer or do not react at all. Halide ions were found to behave as nucleophiles toward the radical cations of thianthrene and p h e n~t h i a z i n e .~~ A more recent thermochemical study demonstrates that the reactivity of the radical cation is mainly determined by oxidation potentials, not by symmetry consideration^.^^ Lerner found that as the chlorine content of PPP increased, the spin concentration decrea~ed.~ The behavior of the polymer toward other nucleophiles was also examined.…”

Section: Scheme I1mentioning

confidence: 99%

Polymerization of aromatic nuclei. XXV. ESR and chemical studies on the radical cation nature of poly(p‐phenylene)

Jones

Kovacic

Howe

1981

J. Polym. Sci. Polym. Chem. Ed.

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SynopsisThe radical cation nature of poly(p-phenylene) (PPP) was examined by electron spin resonance (ESR) and chemical means. ESR studies revealed a radical concentration of 1.0 X 1021 spins/g for the crude polymer. Workup with aqueous acid decreased the value to 1.5 X loL8 spins/g. Reactions of the polymer with certain nucleophiles followed the half-regeneration mechanism, whereas with others, electron transfer mainly occurred. The origin of halogen in the polymer was found to arise from reaction of the radical cation with the oxidant, and not with halide during workup. Oxidation of PPP with various species increased the concentration of radical cations.

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“…Certainly, 11 can be formed in a similar manner. On the other hand, two consecutive S~2-like attacks by R F C O~ or another nucleophile on the methyl groups of 10 or 13 or 14 will give the quinone 8, as illustrated by equation (9).…”

Section: Oxidation Of 1 By (C6f5c02)z In F113mentioning

confidence: 99%

“…With the objective of further testing the viability of the above-mentioned mechanistic proposition, we made a solvent effect study of the reaction with (C6F5C02)~ as the acceptor at 5"C, as summarized in Table2. Conceivably, the nature of the solvents will affect the lifetimes or even the reaction pattern" of CP-I and CP-I1 and also all the reactive intermediates, and it will also affect the relative importance of paths A-C, B, D and E and the S~2-like demethylation reactions exemplified by equation (9). Two interesting features can be seen in Table 2: the yield of 6 increases and that of 8 decreases along the solvent series C6H6, n-C6H14, F113 and CHsCN, as shown by the 618 ratio, and the yield of C6FsCOzBu-t roughly parallels that of 6 and the yield of CbFsCOZMe that of 8.…”

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confidence: 99%

Reactivity and reaction patterns of alkyl alkoxybenzene radical cations. Mechanistic pathways of the reactions between 2,5‐DI‐tert‐Butyl‐1, 4‐Dimethoxybenzene and perfluorodiacyl peroxides

Jiang¹,

Zhao²,

Gong³

1991

J of Physical Organic Chem

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In the reactions of 2,5‐di‐tert‐butyl‐1,4‐dimethoxybezene (1) with different oxidants, the radical cation 1+. is always detectable by EPR. However, the observed reactivity of 1+. depends greatly on the oxidation systems employed. In S2O 82−Cu2+HOAc and Ce4+HOAc systems (HOAc = acetic acid), 1+. appears to have long lifetimes and does not undergo fragmentation spontaneously. In contrast, in (RFCO2)2CF2CICFCI2 (F113) systems, the readily formed 1+. is short‐lived, and large amounts of de‐tert‐butylation products have been isolated. Experimental results imply that the CC bond cleavage involved in de‐tert‐butylation could be a consequence of an attack by perfluoroacyloxy radical on 1+. in their original solvent cage. The fact that addition of methanol to the reaction mixture leads to the formation of a large amount of tBuOCH3 (46%) and other evidence suggest that the tert‐butyl group leaves as a carbocation. On the basis of these results, we conclude that the reactions of 1 with (RFCO2)2 are initiated by electron transfer and followed by a fast coupling of various radical species, namely, 1+. with RFCO2 or with RF in the solvent cage, to form σ‐complexes which collapse or react with nucleophiles to yield the final products.

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Radical ion reactivity—I

Cited by 51 publications

References 67 publications

Substrate selectivity and orientation in aromatic Substitution by molecular fluorine

Substrate selectivity and orientation in aromatic Substitution by molecular fluorine

Polymerization of aromatic nuclei. XXV. ESR and chemical studies on the radical cation nature of poly(p‐phenylene)

Reactivity and reaction patterns of alkyl alkoxybenzene radical cations. Mechanistic pathways of the reactions between 2,5‐DI‐tert‐Butyl‐1, 4‐Dimethoxybenzene and perfluorodiacyl peroxides

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