Structure and Dynamic Behavior of Selected Organolithium Compounds

美国俄亥俄州立大学Gideon Fraenkel教授的有机动力学项目旨在通过核磁共振波谱技术阐明有机锂化合物的结构。此外，俄亥俄州立大学的研究小组将研究有机锂化合物在溶液中聚集的方式。这项工作具有重要的意义，因为有机锂被有机化学家广泛用作合成新的重要化合物的中间体。各种核磁共振技术，包括线形分析和NOE实验，将应用于研究模型溶剂化有机锂化合物的结构和动力学行为，富集Li-6，必要时在α碳上富集C-13，以揭示特定的效应和相互作用。使用极低温度，低至120°K，低浓度，以确保C-Li键交换过程不干扰光谱，将允许观察特定的结构特征。这包括a) RLi - n可能与孤立的双键相互作用；B)配体的溶剂化性质和伴随的热力学；C)烯丙锂的非平面度；d)理论上有趣的二锂化合物的结构。将合成一些手性的顺水二胺和三胺，以观察它们是否稳定不同的（RLi）n聚集体，并确保锂配体的缓慢交换。离子对的结构将通过NOE实验来研究，包括利用偶极耦合的结构依赖性在液晶介质中的离子对。后一种光谱中的交换平均将允许测量离子对之间非常快的离子交换速率。研究人员将分析RLi化合物核磁共振数据中C-13/Li-6偶联的信号平均和物种间的移位，以确定交换速率，并通过动力学和结构信息了解平衡时的交换机制。

This project in the Organic Dynamics Program by Professor Gideon Fraenkel of the Ohio State University is aimed at the elucidation of the structure of organolithium compounds by Nuclear Magnetic Resonance Spectroscopy. In addition, the Ohio State group will investigate the way that organolithium compounds group together in solution (aggregation). This work is highly significant in that organolithiums are widely used by organic chemists as intermediates in the synthesis of new and important compounds. A variety of NMR techniques including line-shape analysis and NOE experiments will be applied to the study of structure and dynamic behavior of model solvated organolithium compounds enriched in Li-6, and if necessary C-13 at the alpha carbon, selected to reveal specific effects and interactions. Use of very low temperature, down to 120 degrees K, and low concentrations to ensure that C-Li bond exchange processes do not perturb the spectra, will allow observation of specific structural features. These include a) possible interactions of (RLi)n species with isolated double bonds; b) nature of ligand solvation and accompanying thermodynamics; c) the degree of non-planarity of allyllithiums; and d) structure of theoretically interesting dilithium compounds. Cisoid diamines and triamines, some chiral, will be synthesized to see if they stabilize different (RLi)n aggregates, and also to ensure slow lithium ligand exchange. The architecture of ion pairs will be studied via NOE experiments including ion pairs in liquid crystal media making use of the structural dependence of the dipolar couplings. Exchange averaging in the latter spectra will allow measurement of very fast rates of exchange of ion among ion pairs. The signal averaging of C-13/Li-6 couplings and shifts among species seen in NMR data for RLi compounds will be analyzed to determine exchange rates, and via kinetics and structural information, to learn about exchange mechanisms at equilibrium.