Heavy Atom Isotope Effect Studies of Organic Reaction Mechanisms

有机反应机理的重原子同位素效应研究

• 批准号: 8713074
• 负责人: Arthur Fry
• 金额: $ 24.35万
• 依托单位: University of Arkansas
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-07-01 至 1990-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8713074&HistoricalAwards=false
• 关键词: Heavy; Atom; Isotope; Effect; Studies

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).

这项有机和大分子化学项目的拨款支持了authurfry教授的研究，该研究旨在通过使用同位素研究反应途径。当一种特定的元素，如氢或碳，被该元素的较重的同位素所取代时，如果同位素本身直接参与反应的缓慢步骤，则可能会注意到反应速率的差异。这是从化学反应中提取机械信息的一种优雅的方法。仅在同位素组成上不同的化合物有时反应速率略有不同（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（如果观察到，则与同位素效应的大小有关）联系起来，可以推断出这些分子反应路径的细节。实验测量和理论计算的同位素效应的相关性被认为是确定化学反应中过渡态结构、过渡态运动和键变化时间的最佳方法之一。该方法最有效的应用于在所有可能发生键变化的位置连续标记的化合物，特别是当取代苯基位于反应中心附近时。本研究利用这些技术来确定各种添加、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去反应、加成反应和取代反应中碳-14同位素效应的测量。正在研究的具体体系包括在取代苯乙烯和肉桂酸衍生物上添加溴和芳基亚砜酰氯；ddt相关化合物和其他2-苯乙基体系的消除反应（elcb样机制）；高度失活（由三氟甲基等）的1-苯乙基体系（El/SN1机制）的溶剂裂解。