Transition State Imbalances in the Deprotonation of Picrylacetophenones by Carboxylate and Phenoxide Bases

Moutiers, Gilles; Fahid, Bouchaïb El; Goumont, Régis; Chatrousse, and Alain-Pierre; Terrier, François

doi:10.1021/jo9518617

Cited by 25 publications

(18 citation statements)

References 52 publications

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“…In these instances, theoretical calculations have been made which indicate that the σ-complexation process results in increases in π-electron density at the 2-,4-and 6-positions as well as on the related NO 2 substituents, accounting well for the variations observed in the corresponding chemical shifts: ∆δC 2,6 = Ϫ17; ∆δC 4 = Ϫ29. 1,38,39 In addition, the calculations confirmed the predominant role of a para-NO 2 group in the delocalization of the negative charge of σ-adducts. That the ∆δC 4 value is here lower for the addition to 3e than to 3i reflects the fact that electron-donation from the N-oxide group to the carbocyclic ring is operating in the benzofuroxan series, 28a so that the C 4 carbon is already initially more shielded in 3e (δC 4 = 125.2) than in 3i (δC 4 = 137.0).…”

Section: Methodsmentioning

confidence: 82%

σ-Complex formation and oxidative nucleophilic aromatic substitution in 4-nitro-2,1,3-benzoxadiazoles

et al. 2003

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The feasibility of carrying out nucleophilic displacement of hydrogen from highly electron-deficient heteroaromatics has been addressed through a detailed investigation of the interaction of a series of nitrobenzofuroxans 3a-i and two related heterocycles 5 and 6, with the 2-nitropropenide anion. Although this series corresponds to a large modulation in the electrophilic properties of the six-membered ring, all reactions first lead to the quantitative formation of the sigma-adducts C-3a-i, C-5 and C-6 arising from covalent addition of the nucleophile to the C-7 carbon. With the exception of the 4-aza substituted member C-5, all the adducts have been isolated as pure and very stable alkali salts. Measurements of the oxidation potentials by cyclic voltammetry reveal that the ease of subsequent hydrogen substitution at carbon-7 strongly decreases with increasing electron deficient character of the six-membered ring. The measured E0 values are in the range 0.5-0.6 V (vs. SCE) for the 4-nitro-benzofuroxan and -benzofurazan adducts (C-3e, C-3i) but they go up to 1.20-1.33 V for the 4,6-dinitro- and 4-nitro-6-trifluoromethanesulfonylbenzofuroxan adducts (C-3a,d) in acetonitrile. Consistently with these E0 values, only very powerful oxidants such as the Ce4+/Ce3+ or the MnO4-/Mn2+ couples can successfully oxidize the adducts leading to the expected substitution products in moderate to good yields (35-72%). Interestingly, the rearomatization of the 4-nitro substituted benzofuroxan adducts proceeds with a partial Boulton-Katritzky rearrangement of the resulting products. Another noteworthy result is that the 4-nitrobenzofuroxan and 4-nitrobenzofurazan molecules suffer competitive addition of the (CH3)2C-NO2- anion to the 5- and 7- positions under some experimental conditions. This represents the first well-defined example of isomeric addition of a carbon nucleophile to these heterocycles.

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Section: Methodsmentioning

confidence: 82%

σ-Complex formation and oxidative nucleophilic aromatic substitution in 4-nitro-2,1,3-benzoxadiazoles

et al. 2003

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“…The key feature in Table 5 is that the intrinsic reactivity of 1 is very low, comparing well with those of nitromethane and phenylnitromethane 3,10 but not with those of the two benzyl cyanides 6a and 6b or the three picryl ketones 7, 8a and 8b. 13,45 Interestingly these five compounds have been shown to ionize with 4. formation of carbanions whose negative charge is essentially delocalized through the nitro substituted phenyl ring.…”

Section: Intrinsic Reactivity Ofmentioning

confidence: 99%

“…formation of carbanions whose negative charge is essentially delocalized through the nitro substituted phenyl ring. 13 Based on intrinsic reactivity data, there is therefore no doubt that (4nitrophenyl)nitromethane behaves essentially as a nitroalkane compound.…”

Section: Intrinsic Reactivity Ofmentioning

confidence: 99%

“…To obtain a better understanding of the reactivity of 1, we have undertaken a thorough structural and kinetic investigation of the ionization of 1 under various experimental conditions. In this paper, we report on the results of both a 1 H and 13 C NMR analysis in various H 2 O-Me 2 SO mixtures, and a kinetic study in a 50 : 50 (v/v) H 2 O-Me 2 SO mixture. Major features of this work will relate to our finding that protonation of the carbanion C-1 occurs at the exocyclic nitro group at low pH and our determination of a very low intrinsic reactivity of 1.…”

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confidence: 99%

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The nitroalkane behaviour of (4-nitrophenyl)nitromethane: a kinetic and structural study in H2O–Me2SO mixtures

Moutiers¹,

Thuet²,

Terrier³

1997

J. Chem. Soc., Perkin Trans. 2

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Rates of proton abstraction from (4-nitrophenyl)nitromethane (1) by a variety of bases B (phenoxide and carboxylate ions, primary amines) and of reprotonation of the resulting carbanion (C-1) by the conjugate acids BH have been measured in a 50 : 50 (v/v) H 2 O-Me 2 SO mixture at 25 ЊC. In contrast with the situation at pH у 4.2 where only one relaxation time corresponding to a simple equilibrium approach according to 1 ϩ B C-1 ϩ BH is observed, the interconversion of 1 and C-1 proceeds in two steps in acidic media. Kinetic studies as well as data obtained by 1 H and 13 C NMR or UV-VIS spectroscopy indicate that the first step corresponds to the protonation of the exocyclic nitro group of C-1, giving rise to the corresponding nitronic acid C-1a,H. All rate and equilibrium parameters obtained for the aci-nitro behaviour of 1, including the log k 0 values measuring its intrinsic reactivity towards the various types of bases studied, emphasize a nitroalkane behaviour rather than a 4-nitrotoluene behaviour of this carbon acid in 50 : 50 (v/v) H 2 O-Me 2 SO. Although they clearly reveal some contribution of the nitrophenyl ring to the stabilization of C-1 in Me 2 SO, the NMR data remain consistent with a major role of the exocyclic nitro group in governing the ionization behaviour of 1 in this dipolar aprotic solvent.

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“…As can be seen, these α elec values (0.32-0.36) are markedly smaller than derived from lines 1 a and 1 b (0.51 and 0.52), apparently indicating that our σ-complexation reactions are characterized by imbalanced transition state structures in which development of resonance and solvation at the carbocyclic ring of electrophile 1 lags behind CÀ C bond formation. [61][62][63] Imbalance values of the order of 0.23-0.26 have also been found for the reactions of 2,4,6-tris(trifluoromethane- sulfonyl)anisole and 2,6-bis(trifluoromethanesulfonyl)-4-nitroanisole with a series of p-substituted anilines in methanol solution at 20°C. [63]…”

Section: Effect Of Nitroalkyl Anion Basicity On Reactiviy and Transitmentioning

confidence: 67%

Electrophilicities of 4‐Nitrobenzochalcogenadiazoles

et al. 2020

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Through the linear free energy relationship log k = s N (N + E), the electrophilicity parameters E of 4-nitrobenzochalcogenadiazoles 1 a and 1 b have been determined, at 20°C, by kinetic investigations of their electrophilic addition reactions to a series of nitroalkyl anions 2 a-c in aqueous solution. The derived E-parameters of electrophiles 1 a (E =-12.80) and 1 b (E =-11.46) have been integrated into the electrophilicity scale established by Mayr. Interestingly the less activated compound (1 a) has an E value which is practically the same as that of the 1,3,5trinitrobenzene (E =-13.19), the common reference aromatic electrophile. Mayr's approach was found to predict the rate constants for σ-complexation reactions of our electrophiles 1 a and 1 b with aniline and 4-chloroaniline in acetonitrile with a factor of 10 À 36. Good linear correlation (r 2 = 0.9979) between the electrophilicity parameters E of 4,6-dinitrobenzochalcogenadiazoles 3 a-c and E values of their analogously 4-nitrobenzochalcogenadiazoles 1 a-c has been found and analysed. Furthermore, effect of basicity of nitronate anions 2 a-c on their nucleophilic reactivity has also been examined quantitatively on the basis of kinetic data. Imbalance effect is suggested to be responsible for the finding of an inequality between the Brønsted α elec and β nuc values.

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Transition State Imbalances in the Deprotonation of Picrylacetophenones by Carboxylate and Phenoxide Bases

Cited by 25 publications

References 52 publications

σ-Complex formation and oxidative nucleophilic aromatic substitution in 4-nitro-2,1,3-benzoxadiazoles

σ-Complex formation and oxidative nucleophilic aromatic substitution in 4-nitro-2,1,3-benzoxadiazoles

The nitroalkane behaviour of (4-nitrophenyl)nitromethane: a kinetic and structural study in H2O–Me2SO mixtures

Electrophilicities of 4‐Nitrobenzochalcogenadiazoles

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