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Chemical and Spectroscopic Studies of Nitrenium Ions and Related Species

氮离子及相关物质的化学和光谱研究

基本信息

批准号：
1900317
负责人：
Daniel Falvey
金额：
$ 45万
依托单位：
University of Maryland, College Park
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-07-15 至 2023-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1900317&HistoricalAwards=false
关键词：
Chemical Spectroscopic Studies Nitrenium Ions

项目摘要

In this project, funded by the Chemical Structure, Dynamics, and Mechanism-B Program of the Chemistry Division, Professor Daniel E. Falvey and his students from the Department of Chemistry and Biochemistry at the University of Maryland, College Park, are investigating the properties and behavior of a class of novel molecular species called nitrenium ions. Nitrenium ions are highly reactive substances with only two bonds to nitrogen and possessing a positive charge. This differs from most nitrogen-containing structures, where nitrogen typically has three bonds and a neutral charge. Under ordinary conditions, nitrenium ions exist for only small fractions of a second. However, it is becoming increasingly apparent that some processes in chemical synthesis, biology and the environment might involve nitrenium ions as intermediates. Understanding and predicting the outcomes of these reactions, therefore, requires accurate information on the properties of nitrenium ions. Professor Falvey and his students are developing methods for producing and observing nitrenium ions under well-defined laboratory conditions. These methods are used to carry out detailed kinetic and spectroscopic measurements on typical nitrenium ions. Experimental results are compared to predictions from state-of-the art computer models, with a goal of refining and improving these predictions. These results will then be available to engineers and scientists who can use them to improve pharmaceutical and agrochemical manufacturing processes, forecast the fate of pollutants in the environment, and understand how the human body interacts with drugs and/or toxins. Professor Falvey actively recruits a diverse group of students, including women and students from traditionally underrepresented groups to participate in these investigations. Students who are engaged in this research gain hands-on experience, synthesizing and characterizing novel chemical species, carrying out quantitative measurements on reaction rates and outcomes, and computer modeling. These experiences prepare them for careers in academia, industry and government. Nitrenium ions are reactive intermediates characterized by a dicoordinate nitrogen atom and bearing a formal positive charge. Nitrogen-containing compounds are ubiquitous, as this element is a component of pharmaceuticals, agrochemicals, high-energy materials, and industrial polymers. Nitrenium ions are intermediates that can form under conditions when nitrogen-containing compounds are oxidized, and/or when the nitrogen atom is substituted with good leaving groups. Nitrenium ions display a wide range of reactivities. Simple alkylnitrenium ions are not even local minima on the singlet potential energy surface, whereas amino-substituted examples are indefinitely stable and can employed as Lewis acids and ligands in metal complexes. Earlier work in Professor Falvey's lab established photochemical methods for the generation of arylnitrenium ions, providing a means for characterizing these species by laser flash photolysis and related methods. The current effort extends these studies to non-arylnitrenium ions, including alkyl, cycloalkyl and heteroarylnitrenium ions. These categories of nitrenium ions have received far less attention, and little is known about their decay reactions, or their stabilities. Some recent calculations indicate that cyclopropyl and cyclobutylnitrenium ions will have non-classical sigma bonding similar to the corresponding carbenium ions. Likewise, the sulfonylnitrenium ions appear to have highly distorted structures, making them far less electrophilic than intuition would suggest. Finally, there are several types of heteroarylnitrenium ions and vinylnitrenium ions that have been predicted to have low energy triplet states. This project aims to resolve fundamental questions about nitrenium ion structure and reactivity. Methodology in this research includes synthesis of photochemical precursors, analysis of stable products from the generated nitrenium ions, spectroscopic and kinetic characterization of nitrenium ions using laser flash photolysis, low temperature electron spin resonance studies of triplet nitrenium ions, and computation studies of nitrenium ion electronic structures and reaction mechanisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在这个由化学部化学结构、动力学和机理b项目资助的项目中，来自马里兰大学帕克分校化学和生物化学系的Daniel E. Falvey教授和他的学生正在研究一类被称为nitrenium离子的新型分子物种的性质和行为。氮离子是一种高活性物质，与氮只有两个键并带正电荷。这与大多数含氮结构不同，氮通常有三个键和一个中性电荷。在一般条件下，氮离子只存在不到一秒的时间。然而，越来越明显的是，在化学合成、生物学和环境中的一些过程可能涉及到氮离子作为中间体。因此，理解和预测这些反应的结果，需要关于氮离子性质的准确信息。法尔维教授和他的学生正在研究在明确的实验室条件下产生和观察氮离子的方法。这些方法对典型的氮离子进行了详细的动力学和光谱测量。实验结果与最先进的计算机模型的预测进行比较，目的是改进和改进这些预测。这些结果将提供给工程师和科学家，他们可以利用它们来改进制药和农用化学品的制造过程，预测环境中污染物的命运，并了解人体如何与药物和/或毒素相互作用。法尔维教授积极招募不同的学生群体，包括女性和传统上代表性不足的群体的学生参与这些调查。参与这项研究的学生将获得动手经验，合成和表征新的化学物种，对反应速率和结果进行定量测量，以及计算机建模。这些经历为他们在学术界、工业界和政府的职业生涯做好了准备。氮离子是一种活性中间体，其特征是一个配位的氮原子并带形式正电荷。含氮化合物无处不在，因为这种元素是药品、农用化学品、高能材料和工业聚合物的组成部分。氮离子是在含氮化合物被氧化和/或氮原子被良好的离去基取代的条件下形成的中间产物。氮离子表现出广泛的反应性。简单的烷基氮离子在单线态势能表面上甚至不是局部最小值，而氨基取代的例子则是无限稳定的，可以用作金属配合物中的路易斯酸和配体。Falvey教授实验室的早期工作建立了生成芳基氮离子的光化学方法，为通过激光闪光光解和相关方法表征这些物种提供了一种手段。目前的努力将这些研究扩展到非芳基氮离子，包括烷基、环烷基和杂芳基氮离子。这些类别的氮离子受到的关注要少得多，而且对它们的衰变反应或稳定性知之甚少。最近的一些计算表明，环丙基和环丁基硝基离子将具有类似于相应的碳离子的非经典sigma键。同样，磺酰基nitrenium离子似乎具有高度扭曲的结构，这使得它们的亲电性远不如直觉所认为的那样强。最后，有几种类型的异芳基氮离子和乙烯基氮离子被预测具有低能三重态。本项目旨在解决有关氮离子结构和反应性的基本问题。本研究的方法包括光化学前体的合成、生成的氮离子稳定产物的分析、利用激光闪光光解对氮离子进行光谱和动力学表征、三态态氮离子的低温电子自旋共振研究以及氮离子电子结构和反应机理的计算研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。