Reaction Trajectories at Nonstereogenic Atoms

这项有机和大分子化学项目的拨款支持伊利诺伊大学Peter Beak教授的研究，旨在确定化学反应过程中原子运动的轨迹。反应轨迹可以被认为是关于化学反应性的最基本的信息，而分子中原子的几何排列的知识为理解分子结构及其与化学反应性的关系提供了基础。然而，这项工作的目的是确定涉及非立体原子的过渡结构的几何形状，这在以前是不可用的。比克博士和他的同事将利用内环限制试验研究非立体异原子反应的轨迹。在这种方法中，原子Z转移的几何形状将通过研究成键原子X和离开原子Y由链连接的系统来评估。在Z从Y到X的转移过程中，一个协调的内环分子内反应所需的环的大小限制了可用的反应几何形状。如果转移具有分子内不能满足的几何要求，则反应变为分子间反应。这些可能性将通过双标记、同位素效应和动力学实验加以区分。还将评估涉及联想和解离步骤的其他机制。研究氧、氮、卤素、氢和硫反应的几何形状。其他机制探针，包括取代基效应和结构重排，将用于提供这些和相关反应的机制信息。

This grant in the Organic and Macromolecular Chemistry Program supports research by Prof. Peter Beak, University of Illinois, aimed at determining the trajectories of atomic motion during chemical reactions. Reaction trajectories may be considered among the most fundamental sorts of information to be derived about chemical reactivity, and knowledge of the geometrical arrangements of atoms in molecules has provided the basis for understanding molecular structure and its relationship to chemical reactivity. However, this work is directed towards determining geometries of transition structures involving nonstereogenic atoms, which heretofore have been unavailable. Dr. Beak and co-workers will investigate the trajectories for reactions at nonstereogenic heteroatoms by use of the endocyclic restriction test. In this approach, the geometry of the transfer of atom Z will be evaluated by investigations of systems in which the bond-forming atom X and the leaving atom Y are joined by a chain. The size of the ring required for a concerted endocyclic intramolecular reaction in the transfer of Z from Y to X limits the available reaction geometry. If the transfer has geometrical requirements which cannot be met intramolecularly, the reaction becomes intermolecular. These possibilities will be distinguished by double labeling, isotope effect, and kinetic experiments. Alternative mechanisms involving associative and dissociative steps will also be evaluated. Investigations of the geometries of reactions at oxygen, nitrogen, halogen, hydrogen and sulfur will be made. Other mechanistic probes, including substituent effects and structural rearrangements will be used to provide mechanistic information about these and related reactions.