Cation Radicals in Solution

有机合成计划支持Nathan L.Bauld教授对溶液中阳离子自由基化学的研究。德克萨斯大学奥斯汀分校化学系的鲍尔德教授正在开发一种方便的机械标准，用于区分烯烃pi键的亲电加成和通过初始电子转移反应进行的加成。通过在芳基乙烯基醚和硫化物上加成亲电体而形成的同苄基阳离子，其中烯烃通过杂原子与芳环绝缘，与Hammett sigma值相关，而这些底物的单电子氧化与Hammett-Brown sigma-plus值相关。相反，当烯烃直接连接到芳环上时，质子化和电离都优先与sigma-plus相关。鲍尔德教授正在开发一套独特的取代基参数，这些参数有望显著改善阳离子自由基形成的相关性，从而区分苯乙烯衍生物的亲电反应和电子转移反应。一种基于连续阳离子自由基反应的新的加成聚合策略为Diels-Alder和其他环加成聚合物提供了一条诱人的途径，将从机理上探索并作为一种新材料的合成方法。德克萨斯大学奥斯汀分校化学系的内森·L·鲍尔德教授在有机合成计划的支持下，对两类反应分子的形成和反应化学进行了研究，一类是带净正电荷的阳离子，另一类是带正电荷的阳离子，除了参与形成分子中化学键的电子外，还含有一个未配对的电子。他正在开发一套参数来描述可以导致这两类分子中的任何一种形成的反应，确定哪些类型的分子会导致简单的阳离子，哪些会导致阳离子自由基。鲍尔德教授研究了一种基于阳离子自由基反应形成聚合物材料的新方法，突显了这些不寻常物种的重要性。这种化学有望提供新材料，并为显示一系列重要性质的已知材料提供更温和的途径。

The Organic Synthesis Program supports Professor Nathan L. Bauld's investigations of the chemistry of cation radicals in solution. Professor Bauld, of the Department of Chemistry of the University of Texas at Austin, is developing a convenient mechanistic criterion for distinguishing electrophilic additions to alkene pi bonds from additions proceeding via initial electron transfer reactions. Formation of homobenzylic cations through addition of electrophiles to aryl vinyl ethers and sulfides, wherein the alkene is insulated from the aromatic ring by virtue of the heteroatom, correlates with the Hammett sigma value, while one-electron oxidation of such substrates correlates with the Hammett-Brown sigma-plus value. In contrast, when the alkene is directly attached to an aryl ring, both protonation and ionization correlate preferentially with sigma-plus. Professor Bauld is developing a unique set of substituent parameters which promise significantly better correlations for cation radical formation, permitting the distinction between electrophilic and electron transfer reactions of styrene derivatives. A new addition polymerization strategy based upon sequential cation radical reactions offers an attractive route to Diels-Alder and other cycloaddition polymers and will be explored mechanistically and as a method for the synthesis of new materials. Professor Nathan L. Bauld, of the Department of Chemistry of the University of Texas at Austin, with support from the Organic Synthesis Program, carries out studies of the formation and reaction chemistry of two classes of reactive molecules, one (`cations`) bearing a net positive charge, the other (`cation radicals`) having a positive charge and also containing an unpaired electron in addition to those electrons involved in forming the chemical bonds in the molecule. He is developing a set of parameters to describe the reactions which can lead to the formation of either of these classes of molecules, determining which types of molecules lead to simple cations and which to cation radicals. The importance of these unusual species is highlighted by Professor Bauld's investigations of a new method for the formation of polymeric materials based upon the reactions of cation radicals. This chemistry promises to afford both new materials and milder routes to known materials displaying a range of important properties.