Solvolytic Reactivity of Heptafluorobutyrates and Trifluoroacetates
作者:Bernard Denegri、Olga Kronja
DOI:10.1021/jo900852u
日期:2009.8.21
A series of X,Y-substituted benzhydryl heptafluorobutyrates (1−6-HFB) and trifluoroacetates (1−6-TFA) were subjected to solvolysis in various methanol/water, ethanol/water, and acetone/water mixtures at 25 °C. The LFER equation log k = sf(Ef + Nf) was used to derive the nucleofuge-specific parameters (Nf and sf) for SN1-type reaction. In comparison with TFA, the HFB leaving group is a better nucleofuge
一系列X,Y的取代的二苯甲基heptafluorobutyrates(1 - 6 -HFB)和三氟乙酸盐(1 - 6 -TFA)在25经受溶剂解在不同甲醇/水,乙醇/水和丙酮/水混合物℃。LFER方程log k = s f(E f + N f)用于得出S N 1型反应的核试剂特定参数(N f和s f)。与TFA相比,HFB离去基团是N f小于0.5单位的更好的核试剂。除非吸电子基团连接在芳环上,否则X,Y取代的三氟乙酸二氢苯酯通过S N 1反应溶剂化。在这种情况下,底物溶剂分解比预期用于S更快Ñ因为在机构的变化的1路线。X,Y取代的二苯甲基heptafluorobutyrates检查这里(Ë ˚F ≥-7.7)溶剂分解根据在S Ñ 1通路。在HFB和TFA的各种溶剂中,几乎平行的log k vs. E f线,以及相应的斜率参数(s f(范围在0.91和0.83之间),表示早期TS,且电荷分离程度适中。均以PCM-B3LYP
Nucleofugality of Aliphatic Carboxylates in Mixtures of Aprotic Solvents and Water
作者:Mirela Matić、Bernard Denegri、Olga Kronja
DOI:10.5562/cca2495
日期:——
The leaving group ability (nucleofugality) of fluoroacetate, chloroacetate, bromoacetate, dichloroacetate, trifluoroacetate, trichloroacetate, heptafluorobutyrate, formate, isobutyrate, and pivalate have been derived from the solvolysis rate constants of the corresponding X,Y-substituted benzhydryl carboxylates in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone, applying the LFER equation: log k = sf (Ef + Nf). The experimental barriers (iota G(double dagger,exp)) for solvolyses of 11 reference dianisylmethyl carboxylates in these solvents correlate very well (r = 0.994 in all solvents) with iota G(double dagger,model) of the model sigma-assisted heterolytic displacement reaction of cis-2,3-dihydroxycyclopropyl trans-carboxylates calculated earlier. Linear correlation observed between the log k for the reference dianisylmethyl carboxylates and the sf values enables estimation of the reaction constant (sf(estim)). Using the iota Gt(double dagger,exp) vs. iota G(double dagger,model) correlation, and taking the estimated sf(estim), the nucleofugality parameters for other 34 aliphatic carbovlates have been determined in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone. The most important variable that determines the reactivity of aliphatic carboxylates in aprotic solvent/water mixtures is the inductive effect of the group(s) attached onto the carboxylate moiety.