Deuterium, proton, and carbon-13 NMR spectra of 1,3,5,7-tetraoxacyclooctane (tetroxocane) were recorded in liquid crystalline and isotropic solutions. as well as in the solid state. In solution, tetroxocane exists as a mixture of the boat-chair (BC) and crown (Cr) conformers. Pseudorotation and inversion is extremely fast in the BC form, while inversion in the crown conformer is relatively slow (on the NMR time scale). Analysis of the NMR line shape and 2D exchange experiments shows that the ring inversion in the Cr form occurs via the BC form. Interconversion rate constants and equilibrium constants between the two forms over a wide temperature range were determined in several normal and liquid crystalline solvents. In the solid state tetroxocane crystallizes in a (slightly distorted) crown form. Deuterium NMR in a powder sample of solid tetroxocane-d(g) exhibits dynamic spectra consistent with molecular 4-fold jumps about their pseudo-C-4 axes. Quantitative analysis of the dynamic line shape is consistent with a small Ct deformation of the molecule, as found previously by X-ray analysis, and yields the following kinetic equation for the jump rate, k(J) (s(-1)) = 5.9 x 10(16) exp (-15.9/RT), where R is in kcal mol(-1) K-1.
Computational and NMR Studies on the Complexation of Lithium Ion to 8‐Crown‐4
作者:Alex van der Ham、Thomas Hansen、Gerrit Lodder、Jeroen D. C. Codée、Trevor A. Hamlin、Dmitri V. Filippov
DOI:10.1002/cphc.201900496
日期:2019.8.16
Lithiumion selective crown ethers have been the subject of much research for a multitude of applications. Current research is aimed at structurally rigidifying crown ethers, as restructuring of the crown ether ring upon ion binding is energetically unfavorable. In this work, the lithiumion binding ability of the relatively rigid 8‐crown‐4 was investigated both computationally by density functional
锂离子选择性冠醚已成为多种应用的大量研究的主题。目前的研究旨在结构上刚性化冠醚,因为离子结合时冠醚环的重组在能量上是不利的。在这项工作中,通过密度泛函理论计算和1 H 和7 Li NMR 光谱实验研究了相对刚性的 8-crown-4 的锂离子结合能力。尽管计算和实验结果都表明 8-crown-4 可以结合锂离子,但与较大的冠醚相比,这种结合较弱。计算分析表明,络合作用是由焓而不是熵驱动的,这说明刚性仅具有名义上的重要性。为了阐明锂离子与冠醚有利相互作用的起源,进行了活化应变分析和能量分解分析,指出有利相互作用本质上主要是静电。8-crown-4是迄今为止报道的能够结合锂离子的最小冠醚,它具有两种不同的构象。
Staudinger; Luethy, Helvetica Chimica Acta, 1925, vol. 8, p. 57
作者:Staudinger、Luethy
DOI:——
日期:——
Clauss,K. et al., Justus Liebigs Annalen der Chemie, 1974, p. 561 - 592
作者:Clauss,K. et al.
DOI:——
日期:——
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