Mechanisms for nucleophilic and photonucleophilic aromatic substitution reactions

Pietra, Francesco

doi:10.1039/qr9692300504

Cited by 69 publications

(28 citation statements)

References 5 publications

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“…1 It was found that two or three nitro groups exert a very powerful effect so that 2,4,6-trinitrochlorobenzene and acyl chloride are comparable in hydrolytic reactivity whereas chlorobenzene requires a higher temperature for hydrolysis. 4,[11][12][13][14][15][16][17] This increase in liability of pyridines to nucleophilic attack is a further reflection for the electronattracting character of the ring nitrogen. [8][9][10] Pyridine derivatives undergo nucleophilic substitution much more easily than the corresponding benzenes, owing to the presence of an electronegative nitrogen atom in the aromatic ring, specially at both 2-and 4positions.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the reaction of 2-chloro-3,5-dinitropyridine withmeta- andpara-substituted anilines in methanol

Hegazy

Fattah

Hamed

et al. 2000

J. Phys. Org. Chem.

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Section: Introductionmentioning

confidence: 99%

Kinetics of the reaction of 2-chloro-3,5-dinitropyridine withmeta- andpara-substituted anilines in methanol

Hegazy

Fattah

Hamed

et al. 2000

J. Phys. Org. Chem.

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“…A variety of o-complexes which are For personal use only. closely analogous to 3 and 4 have been characterized by nmr as well as uv-vis spectroscopy (1)(2)(3)(4)(5)(6)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). However, there is as yet no unambiguous uv-vis or nmr evidence for the carbanions 5 and 6.…”

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confidence: 99%

“…The capability of aromatic nitro compounds to interact with bases by a number of mechanisms has led to controversy regarding the occurrence and importance of nuclear hydrogen exchange (1)(2)(3)(4)(5)(6). In the case of 1,3-dinitrobenzene (DNB), the species that have been postulated to be formed at different times through action of a base Y: are a charge transfer complex 1, a radical anion 2, covalent adducts (also known as Meisenheimer or o-complexes) 3 and 4, as well as the carbanions 5 and 6 which are the presumed intermediates in proton exchange.…”

mentioning

confidence: 99%

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

Buncel¹,

Zabel²

1981

Can. J. Chem.

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ERWIN BUNCEL and ALLEN W. ZABEL. Can. J . Chem. 59, 3177 (1981). Kinetic data have been evaluated for hydrogen exchange in 1,3-dinitrobenzene (DNB), occurring at the 2-position, in dimethylformamide (DMF) -D,O mixtures containing deuteroxide ion. The pseudo first order rate constants for exchange, k,,,. show inverse dependence on the initial DNB concentration, which can be quantitatively related to the extent of o-complex formation in these systems. The profile fork,,,, as function of medium compositio~l exhibits a maximum at ca. 70 mol% DMF, and E ,~, for o-complex formation reaches a plateau at about the same medium composition. The equilibrium constants for o-complex formation, K,, are used to calculate the free. or uncomplexed, deuteroxide ion concentrations, which then allow one to calculate k 2 . the second order rate constants for exchange. The k, values show a uniformly increasing tendency with increased DMF content. Correlations with medium basicity are examined, and the nature of the log k, and log K, vs. H-plots afford insight into the origin of the medium dependence of proton exchange. The results of the present study are consistent with the cr-complex being an unreactive form of the substrate towards exchange, which occurs via uncomplexed DNB present in small concentration. The study also rules out the possibility that the colored species present in these systems is the carbanion formed on deprotonation of DNB.ERWIN BUNCEL et ALLEN W . ZABEL. Can. J. Chem. 59. 3177 (1981). O n a evalue les donnees cinetiques de l'echange d'hydrogene se produisant en position 2 du dinitro-1,3 benzene (DNB) dans des melanges de dimethylformamide (DMF) -D,O contenant I'ion deuteroxyde. L a constante de vitesse d e pseudo ordre un de l'echange k,,,, revele un effet inverse de la concentration initiale de DNB qui peut etre relie quantitativement aux taux deformation du complexe o dans ces systemes. 1.e profil de k,,, en fonction de la composition du milieu montre un maximum pour environ 70 molR de DMF et le E, , , de la formation du complexeo atteint un plateau pour environ la meme composition du milieu. On a utilise la constante d'equilibre d e la formation du complexe o K,, pour calculer les concentrations de I'ion deuteroxyde libre. ou non complexe qui permettent de calculer k, la constante d e vitesse d'ordre deux de I'echange. Les valeurs de k2 montrent une tendance d'augmentation uniforme avec la teneur en DMF. On a examine les correlations avec la basicite du milieu; la nature des courbes de log k, et log K, en fonction de H-fournit des renseignements sur I'origine de l'effet du milieu lors de I'echange de proton. Les resultats de la presente etude sont en accord avec un complexe o qui ne donnerait pas de reaction d'echange celui-ci se produisant par I'intermediaire du DNB non complexe present a une concentration faible. L'etude ecarte egalement la possibilite que l'espece coloree presente dans ces systemes soit le carbanion forme par la protonation du DNB.[Traduit par le journal]

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“…NO,, CN etc., as a general condition for the adduct 2 to be a spectrally detectable species. In cases where X is a displaceable group, these adducts are believed to be formed as reaction intermediates in the overall nucleophilic aromatic substitution (SNAr) process (8)(9)(10).…”

mentioning

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Nucleophilic addition and displacement in the reaction of 2,4,6-trimethylphenoxide ion with 1,3,5-trinitrobenzene. An oxygen-bonded aryloxide σ-complex

Buncel¹,

Moir²,

Norris³

et al. 1981

Can. J. Chem.

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Reaction of 1,3,5-trinitrobenzene with potassium 2,4,6-trimethylphenoxide in dimethyl sulfoxide solution leads to σ-complex formation concurrently with displacement of a nitro group. The results provide definitive evidence for σ-complex formation via the oxygen of aryloxide ion in this system, and contrast with the situation that obtains with phenoxide ion itself, which under corresponding conditions yields the carbon-bonded σ-complex as the product of thermodynamic control. Stereoelectronic factors in σ -complex formation and in the diaryl ether resulting from nitro displacement are also discussed.

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Mechanisms for nucleophilic and photonucleophilic aromatic substitution reactions

Abstract: The term 'ground state' in this Review is used to indicate electronic ground state.

Cited by 69 publications

References 5 publications

Kinetics of the reaction of 2-chloro-3,5-dinitropyridine withmeta- andpara-substituted anilines in methanol

Kinetics of the reaction of 2-chloro-3,5-dinitropyridine withmeta- andpara-substituted anilines in methanol

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

Nucleophilic addition and displacement in the reaction of 2,4,6-trimethylphenoxide ion with 1,3,5-trinitrobenzene. An oxygen-bonded aryloxide σ-complex

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