The Study of Ultrafast Intramolecular Rearrangements via Microwave Dielectric Relaxation

该奖项属于无机、生物无机和有机金属化学项目，将支持利用微波介电弛豫技术对有机金属分子进行快速分子内重排的研究。选择用于研究的系统主要是那些先前由于其重排率而无法通过动态核磁共振技术表征的系统。要研究的体系包括四种配位镍（II）配合物中的四面体-正方形平面相互转换，P、Sb、Ru和Os的三角双锥体化合物中的Berry伪旋转过程，以及Zr、Ce、Th、将测量温度的函数，以便从数据中提取活化能。一段时间以来，人们已经认识到许多分子都经历着各种类型的分子内运动。在许多有机金属化合物的情况下，这些运动可能导致立体异构体的相互转化，并可能对化学反应性产生重要影响。在其他情况下，例如这里要检查的那些，重排是简并的，不会导致分子结构的明显变化。理解这种重排的能量障碍的本质是理解这个过程本身的基础。简并重排经常以如此高的速率发生，以至于很少有实验技术可以利用。微波介电弛豫是一种可以应用于某些化合物的技术。虽然DiCarlo教授所在的主要是一所本科院校，但他的实验室是世界上为数不多的有能力进行这些测量的实验室之一，并提供了一些迫切需要的关于某些重要化合物重排障碍的定量信息。

This award, in the Inorganic, Bioinorganic and Organometallic Chemistry Program, will support studies on very rapid intra- molecular rearrangements of organometallic molecules using the technique of microwave dielectric relaxation. The systems chosen for study are primarily those that have previously resisted characterization by dynamic, NMR techniques because their rates of rearrangement. Systems to be studied include tetrahedral - square planar interconversions in four coordinate nickel(II) complexes, Berry pseudorotation processes in trigonal bipyramidal compounds of P, Sb, Ru and Os, and eight coordinate beta-diketonate complexes of Zr, Ce, Th, and U. Measurements will be made as a function of temperature so that activation energies can be extracted from the data. %%% It has been recognized for some time that many molecules undergo a variety of types of intramolecular motions. In the case of many organometallic compounds these motions may result in the interconversion of stereoisomers and can have important consequences for chemical reactivity. In other cases, such as those to be examined here, the rearrangements are degenerate and result in no apparent change in the structure of the molecule. Understanding the nature of the energy barriers to such rearrangements is fundamental to understanding the process itself. Degenerate rearrangements frequently occur at such high rates that there are very few experimental techniques that can be utilized. Microwave dielectric relaxation is one technique that can be applied to certain compounds. Although Professor DiCarlo is located at a primarily undergraduate institution, his laboratory is one of the few in the world that is equipped to make these measurements and to provide some badly needed quantitative information concerning the barriers to rearrangement in some important classes of compounds.