The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical Study
The radical cation of s-trioxane, radiolytically generated in a freon (CF3CCl3) matrix, was studied in the 10–140 K temperature region. Reversible changes of the EPR spectra were observed, arising from both ring puckering and ring inversion through the molecular plane. The ESREXN program based on th...
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MDPI AG
2014-10-01
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| Series: | Molecules |
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| Online Access: | http://www.mdpi.com/1420-3049/19/11/17305 |
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| author | Sergej S. Naumov Wolfgang Knolle Sergej P. Naumov Andreas Pöppl Igor Janovský |
| author_facet | Sergej S. Naumov Wolfgang Knolle Sergej P. Naumov Andreas Pöppl Igor Janovský |
| author_sort | Sergej S. Naumov |
| collection | DOAJ |
| description | The radical cation of s-trioxane, radiolytically generated in a freon (CF3CCl3) matrix, was studied in the 10–140 K temperature region. Reversible changes of the EPR spectra were observed, arising from both ring puckering and ring inversion through the molecular plane. The ESREXN program based on the Liouville density matrix equation, allowing the treatment of dynamical exchange, has been used to analyze the experimental results. Two limiting conformer structures of the s-trioxane radical cation were taken into account, namely “rigid” half-boat and averaged planar ones, differing strongly in their electron distribution. The spectrum due to the “rigid” half-boat conformer can be observed only at very low (<60 K) temperatures, when the exchange of conformers is very slow. Two transition states for interconversion by puckering and ring-inversion were identified, close in activation energy (2.3 and 3.0 kJ/mol calculated). Since the energy difference is very small, both processes set on at a comparable temperature. In the case of nearly complete equilibration (fast exchange) between six energetically equivalent structures at T > 120 K in CF3CCl3, a septet due to six equivalent protons (hfs splitting constant 5.9 mT) is observed, characteristic of the dynamically averaged planar geometry of the radical cation. DFT quantum chemical calculations and spectral simulation including intramolecular dynamical exchange support the interpretation. |
| first_indexed | 2024-12-11T01:15:07Z |
| format | Article |
| id | doaj.art-d92b2aa401b24de3bd26e363ef202de5 |
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| issn | 1420-3049 |
| language | English |
| last_indexed | 2024-12-11T01:15:07Z |
| publishDate | 2014-10-01 |
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| series | Molecules |
| spelling | doaj.art-d92b2aa401b24de3bd26e363ef202de52022-12-22T01:25:56ZengMDPI AGMolecules1420-30492014-10-011911173051731310.3390/molecules191117305molecules191117305The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical StudySergej S. Naumov0Wolfgang Knolle1Sergej P. Naumov2Andreas Pöppl3Igor Janovský4Ingenieurgesellschaft Auto und Verkehr (IAV GmbH), Rockwellstraße 16, Gifhorn D-38518, GermanyLeibniz-Institute for Surface Modification, Permoserstraße 15, Leipzig D-04318, GemanyLeibniz-Institute for Surface Modification, Permoserstraße 15, Leipzig D-04318, GemanyDepartment of Physics, University of Leipzig, Linnéstraße 5, Leipzig D-04103, GemanyLeibniz-Institute for Surface Modification, Permoserstraße 15, Leipzig D-04318, GemanyThe radical cation of s-trioxane, radiolytically generated in a freon (CF3CCl3) matrix, was studied in the 10–140 K temperature region. Reversible changes of the EPR spectra were observed, arising from both ring puckering and ring inversion through the molecular plane. The ESREXN program based on the Liouville density matrix equation, allowing the treatment of dynamical exchange, has been used to analyze the experimental results. Two limiting conformer structures of the s-trioxane radical cation were taken into account, namely “rigid” half-boat and averaged planar ones, differing strongly in their electron distribution. The spectrum due to the “rigid” half-boat conformer can be observed only at very low (<60 K) temperatures, when the exchange of conformers is very slow. Two transition states for interconversion by puckering and ring-inversion were identified, close in activation energy (2.3 and 3.0 kJ/mol calculated). Since the energy difference is very small, both processes set on at a comparable temperature. In the case of nearly complete equilibration (fast exchange) between six energetically equivalent structures at T > 120 K in CF3CCl3, a septet due to six equivalent protons (hfs splitting constant 5.9 mT) is observed, characteristic of the dynamically averaged planar geometry of the radical cation. DFT quantum chemical calculations and spectral simulation including intramolecular dynamical exchange support the interpretation.http://www.mdpi.com/1420-3049/19/11/17305radical cationss-trioxaneEPRDFTdynamical exchange |
| spellingShingle | Sergej S. Naumov Wolfgang Knolle Sergej P. Naumov Andreas Pöppl Igor Janovský The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical Study Molecules radical cations s-trioxane EPR DFT dynamical exchange |
| title | The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical Study |
| title_full | The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical Study |
| title_fullStr | The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical Study |
| title_full_unstemmed | The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical Study |
| title_short | The Dynamical Behavior of the s-Trioxane Radical Cation—A Low-Temperature EPR and Theoretical Study |
| title_sort | dynamical behavior of the s trioxane radical cation a low temperature epr and theoretical study |
| topic | radical cations s-trioxane EPR DFT dynamical exchange |
| url | http://www.mdpi.com/1420-3049/19/11/17305 |
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