Structure and Rearrangements of Carbocations. The Isotopic Perturbation Method

在有机动力学计划的支持下，桑德斯博士将使用他的同位素微扰方法的扩展来澄清碳正离子中的成键和结构的细节。这种方法利用了多个特定氢气的协同效应，提供了通过对被单个同位素原子取代的分子进行观察而无法获得的信息。实验研究将得到相关从头算量子力学计算的补充。这样做是为了预测碳正离子的结构和能量，也是为了预测平衡同位素效应值，这些值可以与实验获得的相应值进行比较。多重氢的协同效应导致平衡同位素效应，而平衡同位素效应是相互作用的氚原子数目的非线性函数。可能导致非线性同位素效应的快速过程包括围绕单键旋转(改变碳正离子轨道与相邻的C-H和C-C键之间的二面角)。同位素效应的角度依赖性为碳正离子结构的超共轭扭曲提供了一个高灵敏的探针。桑德斯博士的研究项目旨在提高我们对碳正离子的理解，在碳正离子中，与阳离子中心的键的部分成键和立体专一性相互作用(即超共轭)起着重要作用。近年来，实验方法学的新发展和理论计算质量的提高相结合，为碳阳离子重排过程的结构细节和能量表面提供了新的见解。本项目的重点是对桑德斯博士的“同位素微扰法”的实验扩展(在该方法中，多个氚原子产生协同效应，从而产生平衡同位素效应，而平衡同位素效应是氢原子数目的非线性函数)。

With support from the Organic Dynamics Program, Dr. Saunders will employ an extension of his isotopic perturbation method to clarify details of bonding and structure in carbocations. This approach, which takes advantage of the cooperative effects of multiple specific deuteration, affords information which cannot otherwise be obtained via observations made on molecules that are substituted with a single isotopic atom. The experimental studies will be supplemented by relevant ab initio quantum mechanical calculations. This will be done to predict carbocation structures and energies and also to predict equilibrium isotope effect values that can be compared with the corresponding values obtained experimentally. The operation of cooperative effects of multiple deuteration results in equilibrium isotope effects which are non-linear functions of the number of interacting deuterium atoms. Rapid processes, which can lead to non-linear isotope effects, include rotation around single bonds (which varies dihedral angles between carbocation orbitals and neighboring C-H and C-C bonds). The angular dependence of the isotope effects provides a highly sensitive probe of hyperconjugative distortion of carbocation structures. Dr. Saunders' research project is designed to improve our understanding of carbocations, where partial bonding and stereospecific interactions of bonds with cationic centers (i.e., hyperconjugation) play important roles. In recent years, a combination of new developments in experimental methodology and improvements in the quality of theoretical calculations has provided new insight into structural details and energy surfaces for carbocationic rearrangement processes. The present project focuses upon experimental extentions of Dr. Saunders' "isotopic perturbation method" (in which multiple deuteration results in cooperative effects that result in equilibrium isotope effects which are nonlinear functions of the number of deuterium atoms).