动力学研究表明,阴离子亲核试剂OH-,CN-和N 3-与苯甲酰基以及芳氧基部分上具有取代基的苯甲酸芳基酯在25.0的H2O-20 mol%的二甲亚砜中反应这些系统的Hammett log k vs sigma图始终是非线性的。但是,考虑了一种可能的传统解释,该解释涉及速率确定步骤的变化导致具有曲率的四面体中间体的机理,但被拒绝了。提出的解释涉及通过两阶段机理中的苯甲酰基取代基和亲电子羰基中心之间的共振相互作用实现基态稳定。因此,基于Yukawa-Tsuno方程很好地容纳了数据,该方程给出了所有三种亲核试剂的线性图。
Kinetics of the reaction of 4-nitrophenyl benzoates with 4-chlorophenol in the presence of potassium carbonate in dimethylformamide
摘要:
The effect of the substituent in the benzoyl group on the relative rate and activation parameters of transesterification of substituted 4-nitrophenyl benzoates with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate was studied by the competing reaction technique. The whole series of benzoates showed the enthalpy-entropy compensation effect. 4-Nitrophenyl benzoates having electron-acceptor substituents give rise to isokinetic relationship with an isokinetic temperature beta of 382 K. The mechanism of the transesterification process is discussed.
The effect of acyl substituents on the α-effect: contrasting α-effect profiles for reactions of 4-nitrophenyl substituted benzoates with neutral and anionic nucleophiles
作者:Ik-Hwan Um、Hyun-Joo Han、Eun-Kyung Chung
DOI:10.1016/s0040-4039(01)01719-1
日期:2001.11
The magnitude of the α-effect for reactions of 4-nitrophenyl substituted benzoates with a pair of anionicnucleophiles is independent of the electronic nature of the acyl substituent, while the one for the corresponding reactions with a pair of neutral nucleophiles increases as the acyl substituent changes from a strong electron withdrawing substituent to electron donating ones.
Evidence of a stepwise acyl-transfer reaction mechanism: Nonlinear Hammett plots for reactions of p-nitrophenyl substituted benzoates with hydroxide and p-chlorophenoxide
作者:Ik-Hwan Um、Eun-Kyung Chung、Dong-Sook Kwon
DOI:10.1016/s0040-4039(97)01033-2
日期:1997.7
21∼2.44 to 1.45∼1.52 as the acyl substituent becomes a strong electron withdrawing group (σ >0.6). Such a break in the Hammett plots is suggestive of a change in the reaction mechanism and strong evidence of a stepwisemechanism for the acyl-transfer reaction.