Rapid Allylic 1,6 H-atom Transfer In A Criegee Intermediate With Unsaturated Substituents

Qian, Yujie

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https://hdl.handle.net/2142/116612 Copy

Description

Title

Rapid Allylic 1,6 H-atom Transfer In A Criegee Intermediate With Unsaturated Substituents

Author(s)

Qian, Yujie

Contributor(s)

• Lester, Marsha
• Klippenstein, Stephen J.
• Hansen, Anne S.

Issue Date

2022-06-22

Keyword(s)

Mini-symposium: Spectroscopy meets Chemical Dynamics

Abstract

A new allylic 1,6 H-atom transfer mechanism is established through infrared (IR) excitation of the 2-butenal-oxide Criegee intermediate [CH$_{3}$CH=CHCHOO]. Rapid 1,6 H-atom transfer is facilitated for certain conformers of 2-butenal oxide by extended conjugation across the vinyl and carbonyl oxide groups. A low-energy conformer (\emph{tZZ}) of 2-butenal oxide is identified by IR action spectroscopy in the fundamental CH region with ultraviolet (UV) detection of OH products by laser-induced fluorescence (LIF). The strongest observed IR transition at 2996 \wn is consistent with the anharmonic frequency computed for the \emph{tZZ} conformer. A low energy reaction pathway involving isomerization of 2-butenal oxide from a lower energy conformer (\emph{tZZ}) to a higher energy conformer (\emph{cZZ}), followed by 1,6 H-atom transfer via a 7-membered ring transition state with relatively low ring strain, is theoretically predicted and shown experimentally to yield the OH products. The rapid appearance of OH products (ca. 2.3 $\pm$ 1.0 $\times$ 10$^{8}$ s$^{-1}$) agrees with a statistical RRKM calculation for an effective reaction rate (k$_{eff}$(E) on the order of 10$^{8}$ s$^{-1}$ at ca. 3000 \wn) including tunneling. Unimolecular decay involves a combination of conformational isomerization and unimolecular dissociation via 1,6 H-atom transfer. The excellent agreement between experiment and theory confirms the allylic 1,6 H-atom transfer mechanism in 2-butenal-oxide Criegee intermediate and provides a novel pathway for non-photolytic OH generation upon alkene ozonolysis in the troposphere.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Handle URL

https://hdl.handle.net/2142/116612&&

DOI

https://doi.org/10.15278/isms.2022.WH04

Copyright and License Information

Copyright 2022 held by the authors

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