Formation and stability of ring-substituted 1-phenylethyl carbocations
作者:John P. Richard、Marc E. Rothenberg、William P. Jencks
DOI:10.1021/ja00317a031
日期:1984.3
l'utilisation d'azoture et de thiolate en tant que reactifs de piegeage controlant la diffusion afin d'evaluer les constantes de vitesse des reactions des carbocations aryl-1 ethyles avec le solvant et ses composants en fonction de la structure du carbocation, la composition du solvant et la concentration en sel
描述 de l'utilisation d'azoture et de thiolate entant que reactifs de piegeage controlant la diffusion afin d'evaluer les constantes de vitesse des反应 des carboccations aryl-1 ethyles avec le solvant et ses composants en fonction de la structure du carbocation,溶剂组合物和浓缩液
General base catalysis of the addition of hydroxylic reagents to unstable carbocations and its disappearance
作者:John P. Richard、William P. Jencks
DOI:10.1021/ja00317a034
日期:1984.3
Etude de la catalyse basique generale de l'addition d'alcools aux carbocations aryl-1 ethyles
Etude de la catalyze basique generale de l'addition d'alcools aux carboncations aryl-1 乙基
The effects of .alpha.-substituents on the kinetic and thermodynamic stability of 4-methoxybenzyl carbocations: carbocation lifetimes that are independent of their thermodynamic stability
作者:Tina L. Amyes、Ishmael W. Stevens、John P. Richard
DOI:10.1021/jo00074a036
日期:1993.10
The following new rate constants for reaction of alpha-substituted 4-methoxybenzyl carbocations, 4-MeOC6H4CR1(R2)+, With a solvent of 50:50 (v/v) trifluoroethanol/water at 25-degrees-C and ionic strength 0.50 (NaClO4) are reported: 4-MeOC6H4CH(OMe)+, k(S) = 2.2 X 10(7) s-1; 4-MeOC6H4CH(N3)+, k(S) = 3.3 X 10(5) s-1; 4-MeOC6H4C(CH3)2+, k(S) = 1.3 x 10(7) s-1; 4-MeOC6H4CH(CO2Et)+, k(S) = 1.4 X 10(7) s-1; 4-MeOC6H4CCH3(CF3)+, k(S) = 2.5 x 10(7) s-1. The values of k(S) for reaction of 4-MeOC6H4CR1(R2)+ with 50:50 (v/v) trifluoroethanol/water are nearly independent of very large changes in the thermodynamic stability of these carbocations caused by the addition of a wide range of electron-withdrawing or electron-donating groups at the alpha-position. In the most extreme case, the change from an alpha-methoxy to two alpha-(trifluoromethyl) substituents leads to a 23 kcal/mol thermodynamic destabilization of 4-MeOCrH4CR1(R2)+ relative to the neutral azide ion adducts but a 5-fold decrease in its reactivity toward solvent. The data show that the effects of alpha-substituents on the kinetic stability of 4-MeOC6H4CR1(R2)+ are complex and do not parallel the thermodynamic stability of these carbocations. The results are explained by consideration of the polar and resonance effects of the alpha-substituents on both the thermodynamic driving force and the intrinsic barrier for capture of the carbocations by solvent. These reactions are a new example of the consequences of the ''principle of nonperfect synchronization''.41
Reactions of substituted 1-phenylethyl carbocations with alcohols and other nucleophilic reagents
作者:John P. Richard、William P. Jencks
DOI:10.1021/ja00317a032
日期:1984.3
Molecular Recognition of Chiral Diporphyrin Receptor with a Macrocyclic Cavity for Intercalation of Aromatic Compounds
Chiral diporphyrin receptor 1, which has a macrocyclic cavity for the intercalation of aromatic guest molecules, was designed and synthesized from pyrrole in five steps. The binding constants (Ka) ...