Probing the Transition State-to-Intermediate Continuum : Mechanistic Distinction between a Dry versus Wet Perepoxide in the Singlet Oxygen "Ene" Reaction at the Air-Water Interface
A mechanistic study is reported for the reactions of singlet oxygen (1O2) with alkene surfactants of tunable properties. Singlet oxygen was generated either top-down (photochemically) by delivery as a gas to an air-water interface or bottom-up (chemically) by transport to the air-water interface as...
| Veröffentlicht in: | Langmuir : the ACS journal of surfaces and colloids. - 1985. - 38(2022), 19 vom: 17. Mai, Seite 6036-6048 |
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| Weitere Verfasser: | , , , , , |
| Format: | Online-Aufsatz |
| Sprache: | English |
| Veröffentlicht: |
2022
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| Zugriff auf das übergeordnete Werk: | Langmuir : the ACS journal of surfaces and colloids |
| Schlagworte: | Journal Article |
| Zusammenfassung: | A mechanistic study is reported for the reactions of singlet oxygen (1O2) with alkene surfactants of tunable properties. Singlet oxygen was generated either top-down (photochemically) by delivery as a gas to an air-water interface or bottom-up (chemically) by transport to the air-water interface as a solvated species. In both cases, reactions were carried out in the presence of 7-carbon (7C), 9-carbon (9C), or 11-carbon (11C) prenylsurfactants [(CH3)2C═CH(CH2)nSO3- Na+ (n = 4, 6, 8)]. Higher "ene" hydroperoxide regioselectivities (secondary ROOH 2 to tertiary ROOH 3) were reached in delivering 1O2 top-down through air as compared to bottom-up via aqueous solution. In the photochemical reaction, ratios of 2:3 increased from 2.5:1 for 7C, to 2.8:1 for 9C, and to 3.2:1 for 11C. In contrast, in the bubbling system that generated 1O2 chemically, the selectivity was all but lost, ranging only from 1.3:1 to 1:1. The phase-dependent regioselectivities appear to be correlated with the "ene" reaction with photochemically generated, drier 1O2 at the air-water interface vs those with wetter 1O2 from the bubbling reactor. Density functional theory-calculated reaction potential energy surfaces (PESs) were used to help rationalize the reaction phase dependence. The reactions in the gas phase are mediated by perepoxide transition states with 32-41 kJ/mol binding energy for C═C(π)···1O2. The perepoxide species, however, evolve to well-defined stationary structures in the aqueous phase, with covalent C-O bonds and 85-88 kJ/mol binding energy. The combined experimental and computational evidence points to a unique mechanism for 1O2 "ene" tunability in a perepoxide continuum from a transition state to an intermediate |
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| Beschreibung: | Date Revised 18.05.2022 published: Print-Electronic Citation Status PubMed-not-MEDLINE |
| ISSN: | 1520-5827 |
| DOI: | 10.1021/acs.langmuir.2c00279 |