London vs. Keesom and Debye forces: From FTIR cluster spectroscopy of ambivalent alcohol complexes towards intermolecular energy balances

伦敦色散力可以使醇分子的不同氢键对接位点之间的平衡向多功能受体分子倾斜。通过选择在能量近简并对接点之间具有低障碍的系统，并在超音速射流环境中工作，可以用线性红外光谱检测和量化非常细微的能量差异。通过研究大量具有不同色散锚点的系统，可以排除偶然的误差抵消，并且可以系统地揭示量子化学方法在提供所有分子间力的平衡描述方面的细微缺陷。通过选择化学上相似的对接点，非调和零点能量的扭曲效应可以最小化。通过引入手性给体和受体分子，还可以研究分散力介导的手性识别效应。该项目侧重于羰基孤对和烯烃π键面选择，以及氧/π竞争，这是第一个资助期的重点。改进的喷嘴和样品制备设计将被探索。已计划在优先方案中与紫外线/红外和微波专家进行密切的实验合作。除了测试分子间相互作用的量子化学预测外，这些理论方法将与理论小组合作，用于分离和可视化取代基的伦敦色散贡献。最后，利用分子间能量平衡的新概念来探测低温下气相中的伦敦色散相互作用，将通过提供不受体溶剂影响的能量聚焦信息来补充溶液中流行的分子内扭转平衡。

London dispersion forces can tip the balance between different hydrogen bond docking sites of an alcohol molecule to a multifunctional acceptor molecule. By selecting systems with low barriers between energetically nearly degenerate docking sites and by working in a supersonic jet environment, very subtle energy differences can be detected and quantified with linear infrared spectroscopy. By studying a large number of systems with varying dispersion anchors, fortuitous error cancellation can be ruled out and subtle deficiencies of quantum chemical methods in providing balanced descriptions of all intermolecular forces can be uncovered in a systematic way. By choosing chemically similar docking sites, distorting effects from anharmonic zero point energy can be minimized. By including chiral donor and acceptor molecules, chirality recognition effects mediated by dispersion forces can be studied as well. The project concentrates on carbonyl lone pair and alkene π bond face choices, along with the oxygen/π competition, which was in the focus of the first funding period. Improved nozzle and sample preparation designs will be explored. Intense experimental cooperation with UV/IR and microwave experts in the priority programme is planned. Besides testing quantum chemical predictions for intermolecular interactions, such theoretical methods will be used to separate and visualize the London dispersion contribution of substituents in cooperation with theory groups. In the end, the new concept of intermolecular energy balances to probe London dispersion interactions in the gas phase at low temperature will complement the popular intramolecular torsional balances in solution by providing energy-focused information free of bulk solvent influence.