The reaction between acyl halides and alcohols: Alkyl halide vs. Ester formation
作者:Paolo Strazzolini、Angelo G. Giumanini、Giancarlo Verardo
DOI:10.1016/s0040-4020(01)80747-x
日期:1994.4
therefore, ester formation practically confined to a triggering role. But, in those cases where the cation is less easily formed, ester formation was favoured and, consequently, became the necessary elementary step towards alkylhalideformation. This final product, on the other hand, might be extremely slow to form in an SN2 reaction between the protonated ester function and the halideion. In these hnstances
empirical nucleophilicity parameter, and s is a nucleophile-specific slope parameter. From plots of log k versus E of the benzhydrylium ions are derived the solventnucleophilicity parameters s and N, the latter of which are designated as N1 to emphasize that their use in the quoted correlation equation gives rise to first-order rate constants. A linear correlation between N1 and Kevill's solvent nucleophilicity
二苯甲基鎓离子(二芳基碳鎓离子)与不同组成的溶剂混合物(水/乙腈、甲醇/乙腈、乙醇/乙腈、乙醇/水和三氟乙醇/水)的反应速率已通过常规紫外-可见光谱法测定、停流方法和激光闪光技术。已经表明,一阶速率常数遵循先前公布的关系 log k(20°C) = s(N + E),其中 E 是经验亲电性参数,N 是经验亲核性参数,s 是亲核试剂特异性斜率参数。从二苯鎓离子的 log k 与 E 的关系图推导出溶剂亲核性参数 s 和 N,后者被指定为 N1 以强调它们在引用的相关方程中的使用会产生一阶速率常数。报告了 N1 和基于 S-甲基二苯并噻吩鎓离子的 Kevill 溶剂亲核性 NT 之间的线性相关性,这允许将两组数据相互转换。由于 N1 值与之前报道的 pi 系统 (www.cup.uni-muenchen.de/oc/mayr/) 的亲核参数 N 直接相当,因此具有溶剂分解生成的碳正离子的 Friedel-Crafts
Selectivity of Stabilized Benzhydrylium Ions
作者:Bernard Denegri、Mirela Matić、Olga Kronja
DOI:10.1002/ejoc.200901327
日期:2010.3
(2―4―OCO 2 Ph) were subjected to solvolysis in the series of aqueous ethanol, the product ratios were determined and the selectivities (k E /k W ) of the corresponding stabilized benzhydrylium ions 1―4 were calculated. The individual rate constants for ethanolysis (k E ) and hydrolysis (k W ) have been calculated. Ethanolysis proceeds via earlier more carbocation-like transition state than hydrolysis. Due
将碳酸甲酯(1-4-OCO 2 Me)和碳酸苯酯(2-4-OCO 2 Ph)在一系列乙醇水溶液中进行溶剂分解,测定产物比和选择性(k E /k W )计算出相应的稳定二苯甲基离子1-4。已经计算了乙醇分解 (k E ) 和水解 (k W ) 的各个速率常数。乙醇分解通过比水解更早的更类似碳正离子的过渡态进行。由于更重要的溶剂化作用,如果二元溶剂中水的比例增加,则 k E 下降得比 k W 慢,其净效应是选择性对溶剂极性的显着依赖性。由于 log k 与 E 曲线的配对和弯曲,较不稳定的碳正离子 5-8 的选择性降低并受到离去基团的影响。