Direct Nucleophilic Addition versus a Single‐Electron Transfer Pathway of σ<sup>H</sup> Adduct Formation in Vicarious Nucleophilic Substitution of Hydrogen

Mąkosza, Mieczysław; Kwast, Andrzej

doi:10.1002/ejoc.200400034

Cited by 30 publications

(15 citation statements)

References 42 publications

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“…This complex can undergo further transformation in two ways: (1) by heterolytic cleavage of the H-R bond giving p-halonitrobenzene-R Ϫ ion-molecule complex followed by the single electron-transfer (SET) process from R Ϫ to halonitroarene or (2) by homolytic cleavage of the H-R bond yielding directly p-halonitrobenzene radical anion and radical R 52· . The participation of the single electron-transfer step in the aromatic nucleophilic substitution reactions and related processes is an old and intensively discussed problemÅ [31][32][33].Å InÅ principle,Å oneÅ canÅ imagineÅ thatÅ the formation of the -adduct can proceed not only in a direct reaction between the nitroarene and the carbanion but also in a two-step process: (1) single electrontransfer from the carbanion to the nitroarene and (2) recombination of the nitroarene radical anion with the radical formed from the carbanion. Our results show that the SET mechanism can be applied also for rationalization of the gas-phase reactions.…”

Section: Resultsmentioning

confidence: 99%

Aromatic nucleophilic substitution (S_NAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

Danikiewicz

Bieńkowski

Kozlowska

et al. 2007

J. Am. Soc. Mass Spectrom.

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In the gas-phase reactions of halonitro-and dinitrophenide anions with X (X ϭ F, Cl, Br, NO 2 ) and NO 2 groups in ortho or para position to each other with selected C-H acids: CH 3 CN, CH 3 COCH 3 , and CH 3 NO 2 , products of the S N Ar-type reaction are formed. Nitrophenide anions are generated by decarboxylation of the respective nitrobenzenecarboxylate anions in ESI ion source and the S N Ar reaction takes place either in the medium-pressure zone of the ion source or in the collision chamber of the triple quadrupole mass spectrometer. In the case of F, Cl, and NO 2 derivatives, the main ionic product is the respective [NO 2 -Ph-CHR] Ϫ anion (R ϭ CN, COCH 3 , NO 2 ). In the case of Br derivatives, the main ionic product is Br Ϫ ion because it has lower proton affinity than the [NO 2 -Ph-CHR] Ϫ anion (for R ϭ CN, COCH 3 ). For some halonitrophenide anion C-H acid pairs of reactants, the S N Ar reaction is competed by the formation of halophenolate anions. This reaction can be rationalized by the single electrontransfer mechanism or by homolytic C-H bond cleavage in the proton-bound complex, both resulting in the formation of the halonitrobenzene radical anion, which in turn undergoes -NO 2 to -ONO rearrangement followed by the NO

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Section: Resultsmentioning

confidence: 99%

Aromatic nucleophilic substitution (S_NAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

Danikiewicz

Bieńkowski

Kozlowska

et al. 2007

J. Am. Soc. Mass Spectrom.

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“…[19] Experiments with a fast radical clock suggest that formation of the s H adducts proceeds as a one-step nucleophilic addition, not a two-step single-electron transfer and anion radical radical coupling. [20] The overall mechanistic picture of the VNS reaction with carbanions is shown in Scheme 2.…”

Section: Introductionmentioning

confidence: 99%

Substituent Effects on the Electrophilic Activity of Nitroarenes in Reactions with Carbanions

Błażej

Mąkosza

2008

Chemistry A European J

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The effect on electrophilic activity of substituents located para, ortho, and meta to the nitro group of nitrobenzenes was determined by using vicarious nucleophilic substitution of hydrogen (VNS) with the carbanion of chloromethyl phenyl sulfone (1) as the model process. Values for the relative activities of substituted nitroarenes are given relative to nitrobenzene, which was taken as the standard. This process was chosen as a model reaction because it meets key criteria, such as the wide range of substituents that can be present on the nitrobenzene ring, a low sensitivity to steric hindrance, and in particular the possibility of ensuring conditions in which the overall relative rates of reaction in competitive experiments are equal to the relative rates of nucleophilic addition. The values of relative rates of addition, which were taken to be a measure of electrophilic activity, were determined by competitive experiments in which pairs of nitroarenes competed for the VNS reaction with carbanion of 1. A comprehensive set of data for effects of substituents on the electrophilic activity of nitroarenes is presented for the first time.

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“…Therefore, SET dominates, which leads to dimerization of the carbanion and reduction of the nitroarene (Scheme 20). In order to clarify whether SET participates in the VNS and other reactions of α-chlorocarbanions with nitroarenes, experiments with a fast radical clock were carried out (Scheme 21) [49].…”

Section: Does the Addition Proceed Directly Or Via Single-electron Trmentioning

confidence: 99%

Nucleophilic substitution in nitroarenes: a general corrected mechanism

Mąkosza

2019

ChemTexts

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Nucleophilic substitution in electron-deficient arenes is one of the fundamental processes in organic chemistry; however, its mechanism as presented in textbooks does not adequately describe the process. According to this generally accepted mechanism, it is limited to substitution of halogens via nucleophilic addition at positions occupied by halogens. The possibility of addition at positions occupied by hydrogen is totally ignored. Research papers have shown that nucleophilic addition at positions occupied by hydrogen is a fast and reversible process, and σ H adducts are initially formed as intermediates. These σ H adducts can be converted into products of nucleophilic substitution of hydrogen in a few different ways or dissociate so that substitution of halogen can proceed. This general picture is confirmed by many examples presented.

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Direct Nucleophilic Addition versus a Single‐Electron Transfer Pathway of σ^H Adduct Formation in Vicarious Nucleophilic Substitution of Hydrogen

Cited by 30 publications

References 42 publications

Aromatic nucleophilic substitution (S_NAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

Aromatic nucleophilic substitution (S_NAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

Substituent Effects on the Electrophilic Activity of Nitroarenes in Reactions with Carbanions

Nucleophilic substitution in nitroarenes: a general corrected mechanism

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Direct Nucleophilic Addition versus a Single‐Electron Transfer Pathway of σH Adduct Formation in Vicarious Nucleophilic Substitution of Hydrogen

Cited by 30 publications

References 42 publications

Aromatic nucleophilic substitution (SNAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

Aromatic nucleophilic substitution (SNAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

Substituent Effects on the Electrophilic Activity of Nitroarenes in Reactions with Carbanions

Nucleophilic substitution in nitroarenes: a general corrected mechanism

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Direct Nucleophilic Addition versus a Single‐Electron Transfer Pathway of σ^H Adduct Formation in Vicarious Nucleophilic Substitution of Hydrogen

Aromatic nucleophilic substitution (S_NAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

Aromatic nucleophilic substitution (S_NAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase