Reactivity and Lone Pairs: Proton Transfer and Stereoelectronic Effects

有机和高分子化学项目的资助 属于有机反应动力学的子领域，支持 加州大学旧金山分校的查尔斯·佩林博士的研究 迭戈，进入非成键电子对的影响， 化学反应性基本方面的空间定位 例如质子转移速率和立体电子效应。 它 重要的是要了解这些影响和比率， 超快的机械过程，因为它是他们的累积 在宏观世界中被感知为较慢的效果 化学反应。 氮或氧孤对的可用性促进了 发生在皮秒时间尺度上的快速质子转移， 沿着其它重要过程如扩散， 关于单键的轮换和溶剂重组。 根据目前的立体电子控制理论， 当孤对电子是反周面时， 离去基团或进入亲核试剂，但最近 实验结果对这种概括提出了质疑。 第一个研究领域是正在进行的分析的延续 酰胺中的质子交换过程和 铵离子，以探测氢键在 溶剂化离子 现代核磁共振的广泛应用 测量质子交换的仪器 平衡条件下的动力学 这里的一个焦点将 是基板选择性和位置的现象 质子转移的选择性 脒离子转化为氢氧化物。 将寻求证据， 迄今未报道胺催化的协同机理 水的质子交换 在第二个研究领域， 以确定优选的立体化学 孤对电子和反应键之间的关系。 实验系统将包括甲氧基交换动力学 在原酸酯和酰胺缩醛中， 差向异构γ-氨基烯丙醇。 另一种方法 将涉及脒盐水解的产品研究 离子和胍，在脒的反应中， 咪达铵和具有亲核试剂的亚铵离子。 这些 实验的目的是澄清的条件下， 立体电子控制可能是有效的， 有助于提高反应性。

This grant in the Organic and Macromolecular Chemistry Program is in the subfield of organic reaction dynamics, and supports research of Dr. Charles Perrin, University of California at San Diego, into the effects of non-bonding electron pairs and their spatial orientation on basic aspects of chemical reactivity such as proton transfer rates and stereoelectronic effects. It is important to understand these effects and the rates of ultrafast mechanistic processes, since it is their cumulative effect that is perceived in the macroscopic world as slower chemical reactions. The availability of nitrogen or oxygen lone pairs facilitates rapid proton transfer, occurring on a picosecond time scale, along with other important processes such as diffusion, rotation about single bonds, and solvent reorganization. According to current theories of stereoelectronic control, reactivity is increased when a lone pair is antiperiplanar to a leaving group or to an incoming nucleophile, but recent experimental results raise questions about this generalization. The first research area is a continuation of ongoing analyses of proton exchange processes in amides and of rotation in ammonium ion, in order to probe the role of hydrogen bonding in solvating ions. Extensive use is made of modern NMR instrumentation, which permits measurement of proton exchange kinetics under equilibrium conditions. A focal point here will be the phenomena of substrate selectivity and positional selectivity in encounter-controlled proton transfer from amidinium ions to hydroxide. Evidence will be sought for a heretofore unreported concerted mechanism for amine-catalyzed proton exchange in water. In a second research area, attempts will be made to determine the preferred stereochemical relationship between lone pairs and reacting bonds. Experimental systems will include kinetics for methoxy exchange in ortho esters and amide acetals, and of dehydration in epimeric gamma-amino allylic alcohols. An alternative approach will involve product studies in the hydrolysis of amidinium ions and guanidines, and in the reactions of amidinium, imidatonium, and iminium ions with nucleophiles. These experiments are designed to clarify the conditions under which stereoelectronic control might be operative and how much it contributes to increased reactivity.