Structure Determinations of Conformations by NMR

美国国家科学基金会化学部的有机化学和高分子化学计划支持加州理工学院的John D.Roberts教授，他将利用琥珀酸的强氢键单阴离子，通过实验确定其他1，2-二取代乙烷在液晶或溶致溶液中的构象旋转二面角的非常重要的值，并将其扩展到实验中。第二个目标是进一步了解溶剂对Guche构象和反式(反)构象之间平衡位置的影响，特别是那些带有极性、电离和潜在氢键取代基的取代基，这些取代基除了具有重要的化学意义外，还普遍存在于生命系统中的分子中。这一努力将扩展到电子、氢键和溶剂效应与预期的实质性空间效应之间的化合物，后者通常被认为是构象偏好的主要原因，尽管许多经验表明，空间效应对构象偏好的影响基本上不存在或相对较小，除非X和Y取代基都是四面体基团，如叔丁基、三甲基铵、磺酸等。这项研究将深入了解双取代乙烷的构象性质，并对相关的能量学进行实验验证。取代乙烷中的二面角与能量关系直接关系到更好地理解静电和空间位阻对自由能的贡献，不仅影响有机化学，而且与遥远的领域相关，如了解蛋白质侧链结构和动力学。拟议的活动预计会产生几个广泛的影响，特别是通过整合研究和教学，使大学本科生和有动力的高中生受益。有些是加州理工学院的学生，有些来自全国各地，或者来自国外，超过一半是女性。一项计划已经到位，让他们接触到一名新的年轻教职员工的经历的缩影。它首先写一份研究提案，然后让一个知识渊博的教职员工小组对其进行审查。在那里取得成功后，计划如何开始研究工作；学习合成方面的新技术或涉及复杂的仪器；撰写结果以供发表；并以专业化学团体使用的风格在公开会议上提交口头报告或海报。在20年的时间里，110名本科生参与其中，发表了25篇论文，其他几篇基本上是最终稿。该提案列出了9篇论文的标题，其中本科生和高中生的名字是共同作者，30个项目标题列出了学生的名字。这些项目是在2003-2007年期间实施的。

The Organic and Macromolecular Chemistry Program in the Chemistry Division at the National Science Foundation supports Professor John D. Roberts at the California Institute of Technology, who will capitalize on and extend an initial success with the strongly hydrogen-bonded monoanion of succinic acid for determining experimentally by NMR, the very important values of rotational dihedral angles of conformers of other 1, 2-disubstituted ethanes oriented in liquid-crystal or lyotropic solutions. A second objective is to contribute further to understanding the influences of solvents on the positions of equilibria between gauche and trans (anti) conformations, especially ones carrying polar, ionized and potentially hydrogen-bonded substituent groups that, besides being of substantial chemical interest and importance, are ubiquitous in molecules involved in living systems. This effort will be extended to compounds where electronic, hydrogen bonding and solvent effects are to be pitted against expected substantial steric effects, the latter commonly regarded as the primary cause of conformational preferences, even though much experience, shows that steric effects are essentially nonexistent or relatively minor in their influence on conformational preferences, unless the X and Y substituents are both tetrahedral groups, such as tert-butyl, trimethylammonium, sulfonic acid and the like. The research will provide an in-depth understanding of the conformational properties of disubstituted ethanes and experimental validation of the associated energetics. The dihedral angle versus energy relation in substituted ethanes is of direct relevance for developing improved understanding of both electrostatic and steric contributions to the free energy, impacting not only organic chemistry but also being relevant to far removed areas, such as understanding protein side chain structure and dynamics.Broader impacts expected to result from the proposed activities are several, but especially through integrating research and teaching for the benefit of university undergraduates and motivated high-school students. Some are Caltech students, others come country-wide, or from abroad, more than half are women. A program is in place to expose them to a microcosm of the experience of a new young faculty member. It starts with writing a research proposal, then having it reviewed by a knowledgeable faculty group. With success there, planning on how to get the research work started; learning new techniques in synthesis or involving sophisticated instrumentation; writing up the results for publication; and presenting a oral report or poster at a public meeting in the style used by professional chemistry groups. Over a period of 20 years, 110 undergraduates have participated with 25 papers published and several others in essentially final draft form. The proposal lists the titles of nine articles with the names of undergraduates and high school students as co-authors and thirty project titles listing the students' names. These projects were carried out during 2003-2007.