The electron spin resonance spectra of dioxene radical cations

Davies, Alwyn G.; Shields, Charles J.; Evans, Jeffrey; Rowlands, Christopher C.

doi:10.1139/v89-270

Cited by 7 publications

(9 citation statements)

References 8 publications

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The kinetics of the inversion of the dihydrodioxine ring in the radical cations of six dihydrobenzo [1,4]dioxines have been determined by EPR spectroscopy. In the nine compounds for which results are now available, the activation energies E a range from 22.6 to 47.6 kJ mol Ϫ1 , and the pre-exponential factors, log A, from 12.8 to 16.2.

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mentioning

confidence: 99%

“…Dihydro [1,4]dioxines can readily be converted into their radical cations, which can be observed by EPR spectroscopy. The ring inversions occur at a rate which can be measured by monitoring the line shape effects on the signals of the axial and equatorial protons over a range of temperatures, and computer simulation of the spectra gives the rate constants and thence the Arrhenius and Eyring parameters for these reactions.…”

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confidence: 99%

“…We have previously applied this technique to the radical cations of 2,3-dihydro [1,4]dioxine 1 ϩ , 6,7-dimethyl-2,3-dihydro [1,4]dioxine 2 ϩ , and 2,3-dihydrobenzo [1,4]dioxine 3 ϩ . 1…”

mentioning

confidence: 99%

“…The same technique has now been used to determine the kinetics of the inversion of the dioxine ring in the radical cations of 5,8-di-tert-butyl-2,3-dihydrobenzo [1,4]dioxine 4 ϩ , 6,7dimethyl-2,3-dihydrobenzo [1,4]dioxine 5 ϩ , 6,7-dimethoxy-2,3dihydrobenzo [1,4]dioxine 6 ϩ , 2,3,7,8-tetrahydrobenzo[1,2-b; 4,5-bЈ]bis [1,4]dioxine 7 ϩ , 6,7-dihydro-1,3,5,8-tetraoxacyclopenta[b]naphthalene 8 ϩ , and hexahydrobenzotris [1,4]dioxine 9 ϩ . The free energy of inversion in the closed shell parent 9 has also been determined by NMR spectroscopy.…”

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confidence: 99%

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Conformational inversion in dihydrobenzodioxine radical cations

Avila¹,

Davies²,

Lapouyade³

et al. 1998

J. Chem. Soc., Perkin Trans. 2

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mentioning

confidence: 99%

mentioning

confidence: 99%

“…We have previously applied this technique to the radical cations of 2,3-dihydro [1,4]dioxine 1 ϩ , 6,7-dimethyl-2,3-dihydro [1,4]dioxine 2 ϩ , and 2,3-dihydrobenzo [1,4]dioxine 3 ϩ . 1…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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Conformational inversion in dihydrobenzodioxine radical cations

Avila¹,

Davies²,

Lapouyade³

et al. 1998

J. Chem. Soc., Perkin Trans. 2

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“…Computer simulations provide rate constants and, hence the activation parameters for these reactions. This study is reported for 26-28 [99].…”

Section: H Systemsmentioning

confidence: 96%

Electron‐transfer Reactions of Aromatic Compounds

Gescheidt¹,

Khan²

2001

Electron Transfer in Chemistry

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Aromatic molecules are inclined to undergo electron-transfer reactions. The additional charges introduced by the electron-transfer process are efficiently stabilized by delocalization. Nevertheless rearrangements of the molecular skeleton or followup reactions can occur. The course of the electron-transfer reactions and the properties of the species thus formed are the subject of this section.In particular, we concentrate on the species formed after an one-electron transfer reaction. Starting from closed-shell diamagnetic precursors, paramagnetic stages, i.e. radical cations or radical anions are formed in this first step. To understand the properties and reactivity of these species, detailed knowledge in terms of charge and spin delocalization and electronic structure is an important prerequisite. This information is preferably derived from electronic and paramagnetic resonance (EPR and electron-nuclear multiple resonance-techniques such as ENDOR or Triple spectroscopy). It has recently been shown that the experimental results can be substantiated by the use of quantum-chemical calculations. In addition to Hartree-Fock-based ab initio procedures, calculations on the density-functional level of theory have been established as rather efficient tools. Therefore, before representing examples of electron-transfer-generated radicals a short survey of the computational methods is given.Another substantial factor directing the kinetic and thermodynamic stability of charged radicals is ion pairing. This phenomenon, although well established for many years, is often not directly distinct in experiments. To establish the importance of ion pairing, or, in other words, supramolecular interactions, a separate introductory chapter is dedicated to these aspects.The references are selected particularly from recent publications, without, however, ignoring some 'classical' contributions. In some sections topics are included which do not strictly represent aromatic molecules but involve interactions of ztype orbitals.

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