Oxidation Potentials and Chemical Reactivities

这项有机动力学项目的拨款为西北大学的Fred Bordwell博士的研究提供了支持。这项工作分为四个方面：(1)测量中性和带正电的有机化合物的酸强度，(2)估计C-H、N-H和S-H键均解断裂所需的能量，(3)取代基对后者的影响，键断裂过程，以及(4)涉及电子转移的有机反应机制。这项工作将提供深入了解有机反应的途径，特别是那些涉及带负电荷的物种。分子H- a可以很容易地热分裂成两个自由基片段，即H- a给出H原子和a原子，这为其反应性提供了重要的见解。伯德威尔小组最近设计了一种方法，通过结合阴离子的氧化电位及其共轭酸的酸度常数来估计这种键解离能（BDE）的大小，这两种方法都是在二甲亚砜溶液中测量的。这种方法将用于估计大量重要弱酸的BDE，这些弱酸的BDE迄今为止是无法获得的。结合酸和阴离子的氧化势和酸的酸度常数，估计了自由基阳离子的酸度。尽管自由基阳离子作为中间体很重要，但以前还没有这方面的资料。最后，氧化还原电位结合速率研究有望揭示有关阴离子与亲电试剂反应中单电子转移作用的重要新细节。

This grant in the Organic Dynamics Program provides support for the research of Dr. Fred Bordwell of Northwestern University. This work is divided into four areas: (1) the measurement of the acid strength of neutral and positively charged organic compounds, (2) the estimation of the energy required for the homolytic breakage of C-H, N-H and S-H bonds, (3) the effect of substituent groups on this latter, bond breaking process, and (4) organic reaction mechanisms involving the transfer of an electron. This work will provide insight into the pathway of organic reactions, especially those involving negatively charged species. The ease with which a molecule H-A can be cleaved thermally into two radical fragments, i.e., H-A giving H atom and A atom, provides an important insight into its reactivity. The Bordwell group has recently devised a method of estimating the size of such bond dissociation energies (BDE's) by combining the oxidation potential of the anion and the acidity constant of its conjugate acid, both measured in dimethyl sulfoxide solution. This method will be used to estimate BDE's for a large number of important weak acids for which BDE's have hitherto been inaccessible. By combining the oxidation potentials of the acid and the anion, and the acidity constant of the acid, the acidities of radical cations have been estimated. No previous information of this type has been available despite the importance of radical cations as intermediates. Finally, redox potentials combined with rate studies are expected to reveal significant new details concerning the role of single electron transfer in reactions of anions with electrophiles.