Large Phosphorus Hyperfine Coupling as a Sensitive Tool for Studying Molecular Dynamics: ESR and Molecular Mechanics Studies of Ring Interconversion in the cis-2,5-Diphosphoryl-2,5-dimethyl-pyrrolidinoxyl Radical
| Autor: | Paul Tordo, François Le Moigne, Gilles Olive, Didier Siri, Yves Berchadsky, Antal Rockenbauer, Anouk Gaudel-Siri |
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| Přispěvatelé: | Institute of Materials and Environmental Chemistry [Budapest], Research Centre for Natural Sciences, Hungarian Academy of Sciences (MTA)-Hungarian Academy of Sciences (MTA), Chimie, biologie et radicaux libres - UMR 6517 (CBRL), Université de la Méditerranée - Aix-Marseille 2-Université Paul Cézanne - Aix-Marseille 3-Université de Provence - Aix-Marseille 1-Centre National de la Recherche Scientifique (CNRS) |
| Jazyk: | angličtina |
| Rok vydání: | 2003 |
| Předmět: |
010405 organic chemistry
Chemistry Radical Phosphorus chemistry.chemical_element 010402 general chemistry Ring (chemistry) 01 natural sciences Molecular mechanics 0104 chemical sciences Esr spectra [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry Molecular dynamics Hyperfine coupling Computational chemistry Physical chemistry Physical and Theoretical Chemistry |
| Zdroj: | Journal of Physical Chemistry A Journal of Physical Chemistry A, American Chemical Society, 2003, 107, pp.3851. ⟨10.1021/jp0213351⟩ Journal of Physical Chemistry A, 2003, 107, pp.3851. ⟨10.1021/jp0213351⟩ |
| ISSN: | 1089-5639 1520-5215 |
| DOI: | 10.1021/jp0213351⟩ |
| Popis: | International audience; ESR spectra of cis- and trans-β-diphosphorylated pyrrolidine-N-oxyl radicals, c-1 and t-1, were studied in liquid and frozen solution. The expected 1:2:1 triplet (aP (2)) of the 1:1:1 triplet (aN) was observed for t-1; however, for c-1, the inner lines of the 1:2:1 triplet showed a dramatic broadening characteristic of chemical exchange between two equivalent conformations. Owing to the large difference in the hyperfine splitting constants (hfsc) of the exchanging phosphorus (ΔaP ≈ 21 G), the coalescence temperature was unusually high (193 K, in n-pentane), and the potential barrier for ring interconversion (10.5 kJ mol-1) was easily obtained from the temperature dependence of the exchange rate. This value was in very good agreement with the value obtained for an empirical pseudorotational potential (11 kJ mol-1) that was adjusted to fit the temperature dependence of the phosphorus hfsc. For c-1, molecular mechanics calculations gave similar characteristics for the pseudorotational potential and indicated the existence of two identical minima with distorted geometries lying between 3T4 and 3E or 4T3 and E3. For t-1, only the 3T4 conformer was found to be significantly populated. Frozen solution spectra showed that the phosphorus hfsc anisotropy is higher when the C−P bond is pseudoaxial; this result can be explained by a geometry-dependent delocalization of the unpaired electron into the phosphorus 3p orbitals. |
| Databáze: | OpenAIRE |
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