Capto‐dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]

Viehe, H. G.; Merényi, R.; Stella, Lucien; Janousek, Z.

doi:10.1002/anie.197909171

Cited by 380 publications

(97 citation statements)

References 105 publications

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“…This is illustrated in Figure 7, in which the π-and σ-donating properties of the NH 2 and CF 3 groups, respectively, have dramatically different effects on the spatial properties of the R-HOMO. This simple MO explanation, which essentially expands upon the concept of the captodative effect 74,76 and three-electron bonding, 70,98 thus accounts in a general way for the correlation evident in Figure 5.…”

Section: -95mentioning

confidence: 73%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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We have carried out a theoretical study of a series of para-substituted phenoxy radicals in an effort to understand the factors influencing spin and charge density distribution in open-shell systems. The calculations reveal that the distribution of spin and charge are not correlated: cases were found for which spin and charge move together, whereas for other substituents the two quantities exhibit spatially distinct intramolecular polarizations. Charge density variations across the series were found to correlate well with both the Hammett (σ p ) and Hammett-Brown (σ p + ) constants for each substituent, indicating that inductive and/or resonance effects are primarily responsible for the polarization of charge within the molecule. In contrast, the distribution of unpaired spin density could not be adequately accounted for using any of the typical Hammett-type spin delocalization constants cited in the literature. We uncovered an empirical correlation between the polarization of spin density and the R-HOMO-R-LUMO gap of the substituted phenoxy radicals: this led to the development of a simple model based on a three-electron, two-orbital bonding scheme in which mixing between the HOMO of the substituent and the SOMO of the phenoxy moiety serves to define the nature and extent of unpaired spin polarization throughout the molecule. This analysis yielded a correlation coefficient of r > 0.97 for the 15 substituents examined in the study; spin polarization effects in compounds that exhibited the greatest deviation from this correlation could also be readily explained within the context of the model. The underlying reason for the ability to differentially polarize spin and charge likely stems from the fact that net unpaired spin density is completely carried by the unpaired electron (and thus tracks the spatial characteristics of the SOMO), whereas charge density reflects the behavior of all of the electrons of the system. These results could have implications in the field of molecular magnetism, suggesting a means for synthetically tuning the magnitude of intramolecular exchange interactions, as well as providing guidance for the design of catalysts for radical-radical coupling reactions.

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Section: -95mentioning

confidence: 73%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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“…Indeed, due to the presence in its structure of carbon-carbon double bonds conjugated with a carbonyl group, indigoidine can act as a radical scavenger (16). After capture of a radical by one of these double bonds, the newly formed radical will be substituted by both an electronattracting (carbonyl) and an electron-releasing (amine) group and will be particularly stabilized from mutual reinforcement of the two substituent effects (47). Consequently, such a process would be thermodynamically favored.…”

mentioning

confidence: 99%

Characterization of Indigoidine Biosynthetic Genes in Erwinia chrysanthemi and Role of This Blue Pigment in Pathogenicity

et al. 2002

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In the plant-pathogenic bacterium Erwinia chrysanthemi production of pectate lyases, the main virulence determinant, is modulated by a complex network involving several regulatory proteins. One of these regulators, PecS, also controls the synthesis of a blue pigment identified as indigoidine. Since production of this pigment is cryptic in the wild-type strain, E. chrysanthemi ind mutants deficient in indigoidine synthesis were isolated by screening a library of Tn5-B21 insertions in a pecS mutant. These ind mutations were localized close to the regulatory pecS-pecM locus, immediately downstream of pecM. Sequence analysis of this DNA region revealed three open reading frames, indA, indB, and indC, involved in indigoidine biosynthesis. No specific function could be assigned to IndA. In contrast, IndB displays similarity to various phosphatases involved in antibiotic synthesis and IndC reveals significant homology with many nonribosomal peptide synthetases (NRPS). The IndC product contains an adenylation domain showing the signature sequence DAWCFGLI for glutamine recognition and an oxidation domain similar to that found in various thiazole-forming NRPS. These data suggest that glutamine is the precursor of indigoidine. We assume that indigoidine results from the condensation of two glutamine molecules that have been previously cyclized by intramolecular amide bond formation and then dehydrogenated. Expression of ind genes is strongly derepressed in the pecS background, indicating that PecS is the main regulator of this secondary metabolite synthesis. DNA band shift assays support a model whereby the PecS protein represses indA and indC expression by binding to indA and indC promoter regions. The regulatory link, via pecS, between indigoidine and virulence factor production led us to explore a potential role of indigoidine in E. chrysanthemi pathogenicity. Mutants impaired in indigoidine production were unable to cause systemic invasion of potted Saintpaulia ionantha. Moreover, indigoidine production conferred an increased resistance to oxidative stress, indicating that indigoidine may protect the bacteria against the reactive oxygen species generated during the plant defense response.

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“…For personal use only. (etl1ylthio)-3,3-bis(trideuterimmhyl)pent-4 2-bis(ethy1thio)-3,3-dimethylpent-4-en (9) To a solution of 0.292 g (ca. 1.5 mmol) of AgBF4 in acetonitrile was added 0.30 g (1.55 mmol) of methyl 2,2-bis(ethy1thio)acetate (3 I ) followed by 0.19 g (1.25 mmol) of I-bromo-3-methylbut-2-ene.…”

Section: Generalmentioning

confidence: 99%

“…If a radical is substituted by these two electronically complementary groups, the stability of the radical is greatly enhanced since the unpaired electron is delocalized over both the donor and the acceptor groups. This phenomenon has been designated as capto-dative stabilization (9). Finally, the rearrangement may proceed by a concerted pathway (10).…”

mentioning

confidence: 99%

A formal [1,3] sigmatropic reaction involving free radical intermediates: a mechanistic investigation

Bates¹,

Ramaswamy²

1985

Can. J. Chem.

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. 63, 745 (1985).The quantitative isornerization of 2,2-bis(ethylthi0)-3,3-dimethylpent-4-en to 2.2-bis(ethy1thio)-5-methylhex-4-enal was studied over the temperature range 130-170°C. An investigation of the generality and specific mechanism of this formal [I ,3] sigmatropic shift was conducted with six related compounds. The rearrangements were found to obey first-order kinetics, and on the basis of significant positive entropies of activation (52-106 J deg-I mol-I), crossover and trapping experiments, and the lack of a solvent effect (decane vs. DMF), an intermolecular, free-radical chain pathway has been proposed for the isomerization. During the rearrangement of several of the compounds esr signals were observed that were consistent with the presence of the proposed free-radical intermediates. These esr signals have been computer simulated. GORDON S. BATES et S. RAMASWAMY. Can. J . Chem. 63, 745 (1985).OpCrant a des tempCratures allant de 130 170°C, on a CtudiC I'isomCrization quantitative du bis(Cthylthi0)-2,2 dimethyl-3,3 pentkne-4 al en bis(Cthy1thio)-2,2 mCthyl-5 hexknc-4 al. Utilisant six composCs apparent&, on a dCterminC la gCnCralitC et le mCcanisme spCcifique de cette transposition qui est, d'un point de vue formel, du type sigrnatropique [I ,3]. On a trouvC que la cinCtique de ces transpositions est du premier ordre et, sur la base d'entropies d'activation qui sont assez positives (52-106 J deg-' mol-I), d'expkriences d'echanges et de piegeages ainsi que sur Ic fait qu'il n'y a pratiquement pas d'effet de solvant (dCcane vs. DMF), on suggkre que cettc isomCrisation sc produit par le biais d'un proccssus radicalaire intermolCculaire. Au cours des transpositions de plusieurs cornposCs, on a pu observer des signaux de rpe qui sont en accord avec la presence des interrnkdiaires radicalaires proposCs. Utilisant un ordinateur, on a simule ces signaux de rpc.[Traduit par le journal]Although the chemical literature contains many examples of [1,3] alkyl shifts in cyclic systems, their occurrence in acyclic analogues is relatively rare (1). Cookson and Kemp (2) have reported a benzyl migration in the thermal conversion of 3,3-dicyano-2-methyl-4-phenylpent-1 -ene to 1,l-dicyano-2-methyl-4-phenylpent-1-ene which occurs with retention of configuration. Baldwin et al. have evidence for the presence of a radical pathway in the [1,3] sigmatropic rearrangements of a number of systems (3). More recently, Ollis and coworkers (4) have reported rearrangements of various dimethylaminobutenes that again can formally be regarded as [1,3] alkyl shifts. These authors speculate that, although a stereoselective transformation involving a concerted pathway is a likely possibility in the case of several of the compounds, a process involving a weakly interacting radical pair is not unlikely.We recently observed2 a high yielding3 thermal rearrangement of 2,2-bis(ethylthi0)-3,3-dimethylpent-4-enal 1 into compound 2. This rearrangement, which is an example of a [1,3] carbon-carbon shift in an acyclic system, should be favoured si...

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Capto‐dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]

Cited by 380 publications

References 105 publications

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Characterization of Indigoidine Biosynthetic Genes in Erwinia chrysanthemi and Role of This Blue Pigment in Pathogenicity

A formal [1,3] sigmatropic reaction involving free radical intermediates: a mechanistic investigation

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