Heavy Atom Isotope Effect Studies of Organic Reaction Mechanisms

有机化学和高分子化学项目的这笔赠款支持Authur Fry教授的研究，该研究旨在通过使用同位素来研究反应途径。当氢或碳等特定元素被该元素的较重的同位素取代时，如果该同位素本身直接参与了反应的缓慢步骤，则可以注意到反应速度的差异。这是一种从化学反应中提取机械信息的优雅方法。只是同位素组成不同的化合物有时反应速度略有不同(动力学同位素效应)。通过将反应化合物的结构与是否观察到同位素效应(如果是，与同位素效应的大小)联系起来，可以推断出关于这些分子反应路径的细节的许多信息。实验测量和理论计算的同位素效应的关联被认为是确定化学反应中过渡态结构、通过过渡态的运动和成键变化的时间细节的最佳方法之一。当与在怀疑经历成键变化的所有位置连续标记的化合物一起使用时，尤其是当取代苯基位于反应中心附近时，该方法最有效。这项研究利用这些技术来确定各种加成、消除、重排、取代和氧化/还原反应的机理细节。目前的研究主要集中在消除、加成和取代反应中碳14同位素效应的测量。正在研究的具体体系包括将溴和芳基硫基氯化物加成到取代的苯乙烯和肉桂酸衍生物中；与滴滴涕相关的化合物和其他2-苯乙基体系的消除反应(类似ELCB的机理)；以及高度失活的(被三氟甲基等)1-苯乙基体系的溶解(EL/SN1机理)。

This grant in the Organic and Macromolecular Chemistry Program supports the research of Professor Authur Fry, which aims at studying reaction pathways through the use of isotopes. When a particular element like hydrogen or carbon is replaced by a heavier isotope of that element then a difference in the rate of the reaction may be noted if the isotope itself is directly involved in the slow step of the reaction. This is an elegant method of abstracting mechanistic information from chemical reactions. Chemical compounds which differ only in isotopic composition sometimes react at slightly different rates (kinetic isotope effects). By relating the structures of the reacting compounds to whether or not isotope effects are observed (and, if so, to the size of the isotope effects) much information can be deduced about the details of the paths by which these molecules react. Correlation of experimentally measured and theoretically calculated isotope effects is believed to be one of the best methods for determining details of transition state structure, motion through the transition state, and the timing of bonding changes in chemical reactions. The method is most powerful when used with compounds successively labeled at all positions suspected of undergoing bonding changes, and especially when substituted phenyl groups are located near the reaction centers. This research utilizes these techniques in determining mechanistic details for a wide variety of additions, elimination, rearrangement, substitution and oxidation/reduction reactions. Current research is focused on carbon-14 isotope effect measurements in elimination, addition and substitution reactions. Specific systems being studied include additions of bromine and arylsulfenyl chlorides to substituted styrenes and cinnamic acid derivatives; elimination reactions of DDT-related compounds and other 2-phenylethyl systems (Elcb-like mechanisms); and solvolyses of highly deactivated (by triflouromethyl groups, etc.) 1-phenylethyl systems (El/SN1 mechanisms).