The Thermodynamics of Phosphate versus Phosphorothioate Ester Hydrolysis
作者:Jamie Purcell、Alvan C. Hengge
DOI:10.1021/jo0511997
日期:2005.10.1
Phosphorothioate esters are phosphateesters in which one of the nonbridging oxygen atoms has been replaced by sulfur. In the comparative hydrolysis reactions of phosphorothioate and phosphateesters, the sulfur substitution accelerates the rates of the monoesters while slowing the rates of diesters and of triesters. Previously measured enthalpies and entropies of activation for the hydrolysis reactions
硫代磷酸酯是其中一种非桥连氧原子已被硫取代的磷酸酯。在硫代磷酸酯和磷酸酯的比较水解反应中,硫取代加快了单酯的速率,同时减慢了二酯和三酯的速率。将先前测得的单酯,对硝基苯基磷酸酯和对硝基苯基磷酸硫代磷酸酯的水解反应的活化焓和熵与本文测得的二酯,对硝基苯基磷酸乙基乙酯和对硝基苯基硫代磷酸乙酯的活化参数进行比较。的三酯,二乙基p硝基苯基磷酸盐和二乙基p-硝基苯基硫代磷酸酯。在所有三类酯中均发现了硫代磷酸酯类似物具有更大的ΔH consistent的一致趋势。在单酯的情况下,更积极的Δ小号⧧从一种机械的差(d产生Ñ + A Ñ为硫代磷酸酯对甲Ñ d Ñ为磷酸盐)补偿,导致较低的Δ ģ ⧧为硫代磷酸酯单酯。光谱研究表明,与它们的硫代磷酸酯类似物相比,磷酸盐中离去基团的键序没有显着差异,排除了其对始终较高的活化焓的贡献。
Oxygen-18 exchange in nitrophenols: significance for labeling and isotope effect experiments
作者:Alvan C. Hengge
DOI:10.1021/ja00033a075
日期:1992.3
sup 18}O isotope effects in and sup 18}O labelling of nitrophenols is of interest. The authors found and here report that ortho- and paranitrophenols display facile phenolic oxygen exchange in basic solution. Kinetics of these exchange reactions were studied and results of exchange rates are reported. 8 refs., 2 figs., 1 tab.
Examination of P−OR Bridging Bond Orders in Phosphate Monoesters using <sup>18</sup>O Isotope Shifts in <sup>31</sup>P NMR
作者:Kerensa Sorensen-Stowell、Alvan C. Hengge
DOI:10.1021/jo050359b
日期:2005.6.1
monoesters undergo hydrolysis by a loose transition state with extensive bond fission to the leaving group. It has been proposed that part of the high dependence of the rate on the leaving group pKa (βlg = −1.23) arises from weaker ester bonds in the reactants as the pKa of the leaving group decreases, on the basis of X-ray structures and calculations. In contrast, IR and Raman studies suggest that the
有证据表明,磷酸单酯通过松散的过渡态发生水解,并与离去基团发生广泛的键裂变。已经提出,速率的高依赖性部分取决于离去基团p K a(βlg = -1.23),这是由于随着离去基团p K a的降低,反应物中较弱的酯键引起的。 X射线结构和计算。相反,IR和拉曼研究表明,离去基团对溶液中P-OR桥键的长度影响很小。为了收集有关此问题的其他数据,我们在31个样本中使用了18个O同位素位移P NMR监测具有不同离去基团的一系列磷酸酯中P-O键的键序。使用这种技术,我们已经能够评估是否在P-O键的订单观察到桥接和非桥键甲基,乙基,苯乙基,炔丙基,苯基的位置,并且显著变化p硝基苯基磷酸盐使用[ 16 ø 18 ö ]标记在氧化氘中的物质。结果表明,磷酸酯单酯中对磷的桥连和非桥连键序不会因离去基团的p K a的差异或磷酸酯二阴离子的抗衡离子而显着改变。
The Molecularity of the Newman−Kwart Rearrangement
作者:Matthew Burns、Guy C. Lloyd-Jones、Jonathan D. Moseley、Joseph S. Renny
DOI:10.1021/jo1014382
日期:2010.10.1
It was recently reported that the venerable Newman−Kwart rearrangement (1→2) proceeds via mixed first- and second-order kinetics. Prior to this, the rearrangement had been considered to proceed exclusively via an intramolecular OAr→SAr migration. A new bimolecular pathway, possibly involving an 8-membered cyclic transition state, was proposed to account for reaction rates that increased disproportionately
最近有报道说,古老的纽曼-科沃特重排(1 → 2)是通过混合的一阶和二阶动力学进行的。在此之前,人们认为重排仅通过分子内O Ar →S Ar迁移进行。有人提出了一种新的双分子途径,可能涉及一个8元环过渡态,以说明反应速率随微波加热条件下底物浓度的增加而成比例地增加。我们报告了N,N-二甲基O-(对硝基苯基)硫代氨基甲酸酯1a重排的动力学和分子的重新分析在N,N-二甲基乙酰胺溶剂中。使用HPLC,同位素标记(2 H,18 O,34 S)和ESI-ICRMS方法,我们显示没有证据表明双分子途径可以通向2a,并且浓度范围从1a到1a几乎是指数衰减。0.11至4.70M。相反,证明了在微波加热条件下,到微波功率平衡回路的延迟负反馈信号会导致振荡反应过热。由于溶质中较高的tanδ,此振荡的幅度随浓度1a的增加而增加,而这种现象最能解释先前被误解为本质上是一阶和二阶混合的动力学行为。
Malykhin, E. V.; Shteingarts, V. D., Journal of Organic Chemistry USSR (English Translation), 1983, vol. 19, # 10, p. 1926