Probing elusive cations: infrared spectroscopy of protonated acetic acid

Davies, Julia A.; Besley, Nicholas A.; Yang, Shengfu; Ellis, Andrew M.

Abstract

Protonated carboxylic acids, (RCOOH)H+, are the initial intermediates in acid-catalyzed (Fischer) esterification reactions. However the identity of the isomeric form is under debate. Surprisingly, no optical spectra have been reported for any isomer of the protonated carboxylic acid monomer, despite it being a fundamental organic cation. Here, we address these issues by using a new approach to prepare cold He-tagged cations of protonated acetic acid (AA), which entails electron ionization of helium nanodroplets containing metastable dimers of AA. The protonated species is subsequently probed using infrared photodissociation spectroscopy and, following a comparison with calculations, we identify the two isomers whose roles are debated in Fischer esterification. These are the carbonyl-protonated E,Z isomer and the metastable hydroxyl-protonated isomer. Our technique provides a novel approach that can be applied to other elusive ionic species.

Citation

Davies, J. A., Besley, N. A., Yang, S., & Ellis, A. M. (2019). Probing elusive cations: infrared spectroscopy of protonated acetic acid. Journal of Physical Chemistry Letters, 10(9), 2108-2112. https://doi.org/10.1021/acs.jpclett.9b00767

• Journal Article Type: Article
• Acceptance Date: Apr 11, 2019
• Online Publication Date: Apr 11, 2019
• Publication Date: Apr 11, 2019
• Deposit Date: Apr 18, 2019
• Publicly Available Date: Apr 12, 2020
• Journal: The Journal of Physical Chemistry Letters
• Print ISSN: 1948-7185
• Electronic ISSN: 1948-7185
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 10
• Issue: 9
• Pages: 2108-2112
• DOI: https://doi.org/10.1021/acs.jpclett.9b00767
• Keywords: General Materials Science
• Public URL: https://nottingham-repository.worktribe.com/output/1828290
• Publisher URL: https://pubs.acs.org/doi/10.1021/acs.jpclett.9b00767
• Additional Information: This document is the unedited Author’s version of a submitted Work that was subsequently accepted for publication in Journal of Physical Chemistry Letters, copyright © American Chemical Society after peer review. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.jpclett.9b00767