NONLINEAR STRUCTURE-REACTIVITY CORRELATIONS - ACYL TRANSFER BETWEEN SULFUR AND OXYGEN NUCLEOPHILES
NONLINEAR STRUCTURE-REACTIVITY CORRELATIONS - ACYL TRANSFER BETWEEN SULFUR AND OXYGEN NUCLEOPHILES
复制标题
DOI：
10.1021/ja00444a023
复制
发表时间：
1977-01-01
影响因子：
15
通讯作者：
JENCKS, WP
中科院分区：
文献类型：
--
作者：
HUPE, DJ;JENCKS, WP
的Br^nsted型相关性与硫醇碱度的log Kcq的乙酰基转移到一系列的硫醇阴离子有一个斜率，/？cq = 1.38，比质子加成反应的cq值大，但比乙酰基转移到含氧阴离子或氮原子时的deq= 1.6±0.1小。从对硝基噻吩乙酸酯到硫醇阴离子的酰基转移速率常数显示出对硫醇碱度的小敏感性（/3 nuc = 0.27），用于碱性硫醇的速率决定攻击，并且对于比离去基团碱性小的硫醇，急剧断裂到接近0 nuc = 1.0的斜率;这种断裂是由速率决定步骤中的变化引起的，从而导致四面体加成中间体的分解。离去硫醇基团的变化给出了用于速率决定攻击的-0.32的dig的值。碱性硫醇阴离子对取代的乙酸苯酯的攻击表现出类似的行为，具有相同的硫醇碱度依赖性（dnuc= 0.27），并且随着硫醇的PA降低，在dnuc= 0.84的斜率附近出现= 0的断裂，并且酚盐排出成为速率决定。类似地，酚盐离去基团的变化对碱度的依赖性较小，dig=-0.33，对于速率决定攻击和较大的依赖性，dig~-0.9，对于速率决定击穿。取代酚盐离子对硫醇酯的速率决定攻击表现出对酚盐碱度的较大依赖性，dnuc= 0.68，但对醇盐阴离子的依赖性较小（dmic~ 0.2）。与含氧酯乙酸对硝基苯酯的反应也观察到相同的行为。这一突破是由攻击醇盐离子的部分去溶剂化的要求所造成的假设进行了检查。脂肪族硫醇盐阴离子对乙酸对硝基苯酯的反应活性比相应的碱性醇盐阴离子低，但对相应的硫醇酯的反应活性高.尽管酰基转移反应在化学和生物化学中具有重要意义，并且在这一领域进行了大量的研究，但仍有许多方面的问题没有得到完全的理解.这些包括解释进攻和离去基团中的极性取代基对速率和平衡常数的影响，速率决定步骤的性质，一般酸碱催化的机理，以及这些反应是协同进行还是通过涉及亚稳四面体中间体的逐步途径进行的问题。
The Br^ nsted-type correlation with thiol basicity of log Kcq for the transfer of acetyl groups to a series of thiol anions has a slope,/? cq, of 1.38, which is larger than that for the addition of a proton, but smaller than the value of deq= 1.6±0.1 for the transferof acetyl groups to oxyanions or nitrogen. Rate constants for acyl transfer from p-nitrothiophenyl acetate to thiol anions show a small sensitivity to thiol basicity (/3nuc= 0.27) for rate-determining attackof basic thiols and a sharp break to a slope approaching 0nuc= 1.0 for thiols that are less basicthan the leaving group; this break is caused by a change in rate-de-termining step to breakdown of the tetrahedral addition intermediate. Variation of the leaving thiol group gives a value for dig of—0.32 for rate-determining attack. The attack of basic thiol anions on substituted phenyl acetates shows similar behavior with the same dependence on thiol basicity (dnuc= 0.27) and a break near= 0 to a slope of dnuc= 0.84 as the pAof the thiol is decreased and phenolate expulsion becomes rate determining. Similarly, variation of the phenolate leaving group gives a small dependence on basicity, dig=—0.33, for rate-determining attack and a larger dependence, with dig~—0.9, for rate-determining breakdown. The rate-determining attack of substituted phenoxide ions on thiol esters exhibits a large dependence on phenoxide basicity with dnuc= 0.68, but a break to a small dependence (dmic~ 0.2) for alkoxide anions. Identical behavior is observed for reactions with theoxygen ester p-nitrophenyl acetate. The hypothesis that this break is caused by a requirement for partial desolvation of attacking alkoxide ions is examined. Aliphatic thiolate anions are less reactive toward p-nitrophenyl acetate than the corresponding, more basic alcohólate anions, but are more reactive toward the corresponding thiol ester.In spite of the great importance of acyl-transferreactions in chemistry and biochemistry and the large amount of re-search that has been carried out in this area, there are still many facets of these reactions that are incompletely under-stood. These include the interpretation of the effects of polar substituents in the attacking and leaving groups on rate and equilibrium constants, the nature of the rate-determining step, the mechanism of general acid-base catalysis, and the question of whether these reactions are concerted or proceed through stepwise pathwaysinvolving metastable tetrahedral interme-