Studies on the Captodative Effect. Entropy/Enthalpy Compensation as Solvent Effect in Radical Forming Reactions. A Relative Radical Stabilisation Scale
Studies on the Captodative Effect. Entropy/Enthalpy Compensation as Solvent Effect in Radical Forming Reactions. A Relative Radical Stabilisation Scale
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俘虏效应的研究。
DOI：
10.1007/978-94-009-4758-0_23
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
H. Viehe
中科院分区：
文献类型：
--
作者：
R. Merényi;Z. Janousek;H. Viehe
在本文的第一部分中，综述了一些合成、动力学和热力学结果，这些结果证明了二氧化碳(CD)自由基的稳定。第二部分给出了在自由基形成反应(均解解离，[2+2]环加成)中溶剂效应表现为热熵补偿的几个例子。这一现象对于具有几个极性取代基的化合物尤其重要，例如Cd-自由基。等动力学温度在或接近测量的温度范围内，导致溶剂对速率的影响可以忽略不计。第三部分提出了一个相对自由基稳定化标度(RRSX)，它给出了一个关于取代基效应大小的概念，如果存在两个或三个取代基，它可以用来估计加成程度。它是基于几个相关的物理化学测量的平均值。
In the first part of this paper, some synthetic, kinetic and thermodynamic results are reviewed showing evidence for the captodative (cd) radical stabilisation.The second part gives several examples for manifestation of solvent effects as enthalpy-entropy compensation in radical forming reactions (homolytic dissociations, [2+2] cycloadditions). This phenomenon is particularly important for compounds with several polar substituents such as cd-radicals. Isokinetic temperatures are in/or near to the temperature domain of measurements leading to negligible solvent effects on rate. A hypothesis is developed proposing the explanation of this phenomenon by the change of polarisation when a radical is formed (“Radical Umpolung”).In the third part a Relative Radical Stabilisation Scale (RRSX)is proposed, which gives an idea concerning the magnitude of the substituent effects and which can be used to estimate the degree of additivity if two or three substituents are present. It is based on average values of several correlating physicochemical measurements.