Evidence for Oxonium Ions in Ethereal "Hydrogen Chloride"

25 October 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Although solutions of hydrogen chloride in ethereal solvents like diethyl ether or dioxane are commonly employed in the laboratory, the solution structure of these reagents has yet to be firmly established. Here, we analyze solutions of ethereal hydrogen chloride or deuterium chloride in toluene, dichloromethane, or in the absence of cosolvent by in situ IR spectroscopy. The resulting spectra are inconsistent with free HCl or often-proposed 1:1 HCl:ether complexes, but closely match the predicted spectra of oxonium ions generated via protonation of diethyl ether. Molecular dynamics simulation of the oxonium chloride complexes provides evidence for an outer-sphere contact ion pair. These results suggest new approaches for tuning the acidity of strong Brønsted acids in organic solvents and demonstrate the importance of conducting spectroscopic measurements under reaction-relevant conditions.


in situ IR
solution structure
ab initio molecular dynamics

Supplementary materials

Supporting Information
Experimental and computational methods.


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.