15573-49-6Relevant academic research and scientific papers
Nucleophilic displacement at the benzoyl centre: A study of the change in geometry at the carbonyl carbon atom
Colthurst, Matthew J.,Williams, Andrew
, p. 1493 - 1497 (2007/10/03)
The second-order rate constants for the reaction between hydroxide ion and phenoxide ion with 4-nitrophenyl esters of substituted benzoic acids in 10% acetonitrile-water (v/v) solution obey Hammett σ correlations. The values of the Hammett ρ of 1.67 (κArO) and 2.14 (κOH) are consistent with a large change in hybridization at the central carbon by comparison with the ρ value for a standard reaction where a full sp2 to sp3 change occurs. The transition state for the concerted reaction thus has a substantially tetrahedral geometry. The observation of the anti-Hammond effect whereby the ρ value for the hydroxide ion exceeds that of the less reactive phenoxide ion is consistent with a concerted, ANDN, mechanism for these reactions. A stepwise mechanism, AN + DN, is unlikely to yield a measurable break in the Hammett correlation for a change in the benzoyl substituent if the partitioning of the putative tetrahedral intermediate involves forward and reverse reactions with Hammett correlations possessing similar ρ values.
The Stabilities of Meisenheimer Complexes. Part 42. Kinetic Studies of the Reactions of Methyl 3,5-Dinitrobenzoate and of Methyl 4-Chloro-3,5-dinitrobenzoate with Hydroxide ions in Dimethyl Sulphoxide-Water Mixtures. Competitive Nucleophilic Attack at Aryl and Carbonyl Carbon Atoms
Crampton, Michael R.,Greenhalgh, Colin
, p. 873 - 878 (2007/10/02)
Kinetic and equilibrium data, obtained by stopped-flow spectrophotometry, are reported for the reactions of methyl 3,5-dinitrobenzoate (1) and methyl 4-chloro-3,5-dinitrobenzoate (5) with hydroxide ions in dimethyl sulphoxide-water mixtures.There is evidence for competition between attack at carbonyl and aryl carbon atoms, the latter becoming relatively favoured as the proportion of dimethyl sulphoxide in the solvent is increased.It is shown that the major pathway in the formation of 4-hydroxy-3,5-dinitrobenzoate from (5) involves hydroxide attack at the carbonyl function followed by slow attack at the ring carbon atom carrying chlorine.
Formation and Stability of Ring-Substituted 1-Phenylethyl Carbocations
Richard, John P.,Rothenberg, Marc E.,Jencks, William P.
, p. 1361 - 1372 (2007/10/02)
The solvolysis of 1-phenylethyl derivatives with electron-donating 4-substituents in 50:50 trifluoroethanol:water(v:v) occurs at a rate that is independent of azide concentration but gives yields of the corresponding azide adducts of up to 98percent by trapping a carbocation intermediate.Rate constants for reactions of the cations with solvent range from 2 x 103 s-1 (4-Me2N) to 4 x 109 s-1 (4-Me), assuming a diffusion-controlled rate constant of 5 x 109 M-1 s-1 for their reactions with azide and thiol anions.Correlation of the rate constants following the Yukawa-Tsuno treatment gives ρn = 2.5, ρr = 5.2, and r+ = 2.1 for the reaction with trifluoroethanol, and ρn = 2.7, ρr = 4.9, and r+ = 1.8 for the reaction with water.The reverse reaction, acid-catalyzed cleavage of substituted 1-phenylethyl alcohols to give the corresponding carbocation, follows ρn = -4.9, ρr = -4.4, and r+ = 0.9.This gives values of ρn = -7.6, ρr = -9.3, and r+ = 1.2 for formation of the cations at equilibrium.There is an imbalance in the development of resonance delocalization, analogous to the "nitroalkane anomaly", that is consistent with a dependence of the fraction of maximal resonance delocalization on the fraction of rehybridization or C-X bond cleavage.Solvent effects on carbocation stability in aqueous-organic mixtures are relatively small.They depend mainly on the nucleophilicity of the solvent components and a specific solvent effect of trifluoroethanol on the reactivity of hydroxylic nucleophiles, including trifluoroethanol itself.The "ionizing power" of the solvent has only a small effect on cation stability, and there is little effect of the concentration or nature of added salts.
