Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392 Giessen, Germany.
J Am Chem Soc. 2021 Jan 13;143(1):41-45. doi: 10.1021/jacs.0c09597. Epub 2020 Dec 15.
We present a comprehensive experimental study of a di--butyl-substituted cyclooctatetraene-based molecular balance to measure the effect of 16 different solvents on the equilibrium of folded versus unfolded isomers. In the folded 1,6-isomer, the two -butyl groups are in close proximity (H···H distance ≈ 2.5 Å), but they are far apart in the unfolded 1,4-isomer (H···H distance ≈ 7 Å). We determined the relative strengths of these noncovalent intramolecular σ-σ interactions via temperature-dependent nuclear magnetic resonance measurements. The origins of the interactions were elucidated with energy decomposition analysis at the density functional and levels of theory, pinpointing the predominance of London dispersion interactions enthalpically favoring the folded state in any solvent measured.
我们进行了一项关于二丁基取代环辛四烯基分子天平的综合实验研究，以测量 16 种不同溶剂对折叠型与展开型异构体平衡的影响。在折叠的 1,6-异构体中，两个丁基基团非常接近（H···H 距离≈2.5Å），但在展开的 1,4-异构体中它们相隔很远（H···H 距离≈7Å）。我们通过温度依赖的核磁共振测量确定了这些非共价分子内 σ-σ 相互作用的相对强度。通过密度泛函和理论水平的能量分解分析阐明了相互作用的起源，指出在测量的任何溶剂中，伦敦色散相互作用的焓有利于折叠态。
