Conformer-Dependent Chemistry: Experimental Product Branching of the Vinyl Alcohol + OH + O₂ Reaction
Abstract
The concentration of formic acid in Earth's troposphere is underestimated by detailed chemical models compared to field observations. Phototautomerization of acetaldehyde to its less stable tautomer vinyl alcohol, followed by the OH-initiated oxidation of vinyl alcohol, has been proposed as a missing source of formic acid that improves the agreement between models and field measurements. Theoretical investigations of the OH + vinyl alcohol reaction in excess O₂ conclude that OH addition to the α carbon of vinyl alcohol produces formaldehyde + formic acid + OH, whereas OH addition to the β site leads to glycoaldehyde + HO₂. Furthermore, these studies predict that the conformeric structure of vinyl alcohol controls the reaction pathway, with the anti-conformer of vinyl alcohol promoting α OH addition, whereas the syn-conformer promotes β addition. However, the two theoretical studies reach different conclusions regarding which set of products dominate. We studied this reaction using time-resolved multiplexed photoionization mass spectrometry to quantify the product branching fractions. Our results, supported by a detailed kinetic model, conclude that the glycoaldehyde product channel (arising mostly from syn-vinyl alcohol) dominates over formic acid production with a 3.6:1.0 branching ratio. This result supports the conclusion of Lei et al. that conformer-dependent hydrogen bonding at the transition state for OH-addition controls the reaction outcome. As a result, tropospheric oxidation of vinyl alcohol creates less formic acid than recently thought, increasing again the discrepancy between models and field observations of Earth's formic acid budget.
Additional Information
© 2023 American Chemical Society. Published as part of The Journal of Physical Chemistry virtual special issue "Marsha I. Lester Festschrift". This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under Contract No. DE-ACO2-05CH11231. C. J. P., S. P. S., and F. A. F. W. gratefully acknowledge support from the NASA Tropospheric Composition and Upper Atmosphere Research Programs. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. M. D. S. was supported by a NASA FINESST Fellowship NNX16AO36H. A. H. was supported by the NASA Jet Propulsion Laboratory. G. H. J. and M. O. were supported by the National Science Foundation grant CHE-1413712. D. R., R. A., and D. L. O. are supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences (BES), US Department of Energy (USDOE). Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the USDOE's National Nuclear Security Administration under Contract DE-NA0003525. Argonne National Laboratory is supported by the USDOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences under Contract No. DE-AC02-06CH11357. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the USDOE or the US Government. The authors declare no competing financial interest.Additional details
- Eprint ID
- 121321
- Resolver ID
- CaltechAUTHORS:20230504-446162300.4
- DE-ACO2-05CH11231
- Department of Energy (DOE)
- NASA/JPL/Caltech
- NNX16AO36H
- NASA Earth and Space Science Fellowship
- CHE-1413712
- NSF
- DE-NA0003525
- Department of Energy (DOE)
- DE-AC02-06CH11357
- Department of Energy (DOE)
- Created
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2023-05-05Created from EPrint's datestamp field
- Updated
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2023-05-05Created from EPrint's last_modified field