Close Non-Bonded Contacts: Effects on Structure and Conformational Reactions

在这个由化学部门化学结构、动态和机制B项目资助的国家科学基金项目中，杜兰大学化学系的Robert Pascal教授制备了新的化合物，这些化合物含有相互作用的官能团，这些官能团在非常接近但不成键的接触和/或相互作用的分子表面，其接触程度随构象而变化。其中一些分子很可能在键距和非键接触距离上表现出“世界纪录”的缩短。这些化合物中有许多具有非常不寻常的形状，在自然界中基本上是未知的。这项研究在本质上是基础性的，将提高我们对化学键的理解。这些化合物还可能具有独特的手性和光物理性质，这将使它们成为手性催化剂、手性传感器或有机电子材料的候选材料。它们还对化学和生物科学中广泛使用的计算方法的准确性提供严格的测试。这项研究非常适合培训各个层次的实验室化学家，包括来自科学界代表性不足群体的学生。在环烷中，复杂的多苯基芳香族分子和含有强相互作用表面的多环芳香族结构有一个共同的特征：传统的和分散校正的密度泛函理论（DFT）计算对它们的描述完全不同，但这些方法中哪一种更符合实验？(1)所提出的in，in-cyclophanes包含沿分子中心轴非常紧密地压在一起的官能团，但两种类型的DFT计算给出了显着不同的原子间距离。(2)所提出的多苯基芳烃具有手性最低能构象，但两种类型的DFT计算给出的外消旋化势垒差异很大。(3)与芳香多环相互作用的分子可能采用不同的构象，使分子内范德华相互作用最大化或最小化，但两种类型的DFT计算为它们的相互转化提供了非常不同的平衡常数。x射线晶体学、动态核磁共振光谱、手性载体的色谱分辨率和核磁共振平衡常数的测定被用来判断各种计算方法的准确性。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。

In this NSF project, funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Robert Pascal, Jr. of the Department of Chemistry at Tulane University prepares new compounds that contain interacting functional groups in very close, but non-bonded contact and/or interacting molecular surfaces whose extent of contact varies with conformation. Some of these molecules are likely to exhibit "world record" shortening of bond distances and non-bonded contact distances. Many of these compounds have highly unusual shapes that are essentially unknown in the natural world. The research is fundamental in nature and will improve our understanding of chemical bonding. These compounds may also possess unique chiroptical and photophysical properties that would make them candidates for chiral catalysts, chiral sensors, or organic electronic materials. They also provide stringent tests of the accuracy of computational methods that are widely used in the chemical and biological sciences. The research is ideal for the training of laboratory chemists at all levels, including students from underrepresented groups in science.In,in-cyclophanes, complex polyphenyl aromatic molecules, and polycyclic aromatic structures containing strongly interacting surfaces share a common feature: conventional and dispersion-corrected density functional theory (DFT) calculations describe them quite differently, but which of these methods better agrees with experiment? (1) The proposed in,in-cyclophanes contain functional groups pressed very close together along the central axes of the molecules, but the two types of DFT calculations give significantly different interatomic distances. (2) The proposed polyphenyl aromatics have chiral lowest-energy conformations, but the two types of DFT calculations give very different barriers for racemization. (3) The proposed molecules with interacting aromatic polycycles may adopt distinct conformations that either maximize or minimize intramolecular van der Waals interactions, but the two types of DFT calculations give very different equilibrium constants for their interconversion. X-ray crystallography, dynamic NMR spectroscopy, chromatographic resolution on chiral supports, and NMR determination of equilibrium constants are being employed to judge the accuracy of the various computational methods.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.