Hydrocarbon Radical Cations in Condensed Phases

Lund, Anders; Lindgren, Mikael; Lunell, Sten; Maruani, J.

doi:10.1007/978-94-009-2853-4_11

Cited by 15 publications

(10 citation statements)

References 163 publications

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“…18 Each state is associated with a particular geometrical distortion and distribution of the unpaired electron.' ' , 1 8 These are summarized as shown above 10 G = 1 mT. l,c3-Me2-cC6: 1 ,c-3-dimethylcyclohexane; l,r3-1LIe2-cC6: 1, r-3-dimethylcyclohexane; 1,c3,t5-Me3-cC6: l,c-3,r-5-trimethylcyclohexane; l,c3,c5-Me3-cC6: with schematical SOMOs as projected in the averaged ring plane.…”

mentioning

confidence: 99%

Radical cations of cis- and trans-1,3-di- and 1,3,5-trimethylcyclohexanes. Matrix influence on two nearly degenerate SOMOs

Lindgren¹,

Matsumoto²,

Shiotani³

1992

J. Chem. Soc., Perkin Trans. 2

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Radical cations of cis and trans isomers of 1,3-di-and 1,3,5-tri-methyIcyclohexane, stabilized in various y-irradiated solute-halocarbon matrices at 77 K and above, have been investigated b y means of EPR spectroscopy. The hfs constants have been compared w i t h those calculated using semiempirical methods, I NDO (spin density) and MN DO (geometry optimizations). The SOMOs of the methyl-substituted cyclohexane cations are all similar t o either of the orbitals, a, or b, , following a Jahn-Teller split of the e, orbital (HOMO) of cyclohexane. The selection of SOMO depends on matrix and isomer. The trans isomers have one axial methyl group and the cations were found to take an a,-like SOMO in all matrices used, with large spin density o n the equatorial hydrogen attached t o the axially substituted ring-carbon. Using CF,CCI, as matrix the EPR signal due to the trans-l,3,5-trimethylcyclohexane cation contains (in addition) a spectrum of the b,-like SOMO superimposed. The cation of cis-I ,3-dimethylcyclohexane shows contributions from both SOMOs in the matrices CF,-cC,F,,, CF,CICFCI, and CF3CCI3, but exclusively a b,-like SOMO in cC6F12. A b,-like SOMO is observed for the cis-l,3,5-trimethylcyclohexane cation in all matrices. The abundance ratios, [a,]/[b,],for the cases where the matrix-stabilized cation shows contribution from both b,and a,-like SOMOs simultaneously, are found t o be ca. 1/4 from line shape simulations. No prominent temperature dependence of this ratio is detected. 'A" ( C,) A'(C,) 'A" (C,) 'A'(C,) ' A' ( C J 'A'K,) ' A" (C,) 'A"(C,)36 (2 H); 29 (2 H) 93 (2 H); 12 (2 H ) 38 (2 H); 29 (2 H) 107 (1 H); 64 (1 H); 35 ( I H) * 1 cal = 4.184 J.

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confidence: 99%

Radical cations of cis- and trans-1,3-di- and 1,3,5-trimethylcyclohexanes. Matrix influence on two nearly degenerate SOMOs

Lindgren¹,

Matsumoto²,

Shiotani³

1992

J. Chem. Soc., Perkin Trans. 2

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“…To a large extent this effect is assumed to be due to the strong attenuation of reactivity experienced by many nucleophiles [ 981. Dihydro [ 1,4]dioxines can readily be converted into their radical cations, the ring inversion occurs at a rate which can be measured by monitoring line shape effects on signals of axial and equatorial protons over a range of temperatures. Computer simulations provide rate constants and, hence the activation parameters for these reactions.…”

Section: H Systemsmentioning

confidence: 99%

“…The g-factors of the radical cations comply with the values for oxidized S-donors, whereas those of the corresponding anions are typically of reduced n-systems without heteroatoms. The new derivative 8,9-bis(methylsulfanyl)-acenaphtho [ 1,2-b] [ 1,4]dithiine has emerged as a promising electron donor for the formation of crystalline charge-transfer complexes and radical ion salts, X-ray crystal structures have been obtained for its 1:l complexes with TCNQ and BrZTCNQ. In his extensive study of the UV spectra of organic thiocarbonyl compounds, Janssen [422] included some sodium dithiocarbamates based on primary and secondary aliphatic amines.…”

Section: Heteronuclear Radical Anionsmentioning

confidence: 99%

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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“…The near degeneracy of the lower two states results through the Jahn-Teller distortion of highly symmetric radical cations [51,52]. The gap between the two lower states is greater for methylcyclohexane^+ and cis-decalin^+ and these two radical cations exhibit more regular magnetic resonance behavior.…”

mentioning

confidence: 99%

“…Indeed, both matrix-isolation EPR experiments and quantum-mechanical calculations indicate that the neutral cycloalkanes and their ground-state radical cations have rather different geometries [50,51,52]. For example, in cis-and trans-decalins the bridging C 9 -C 10 bond elongates from 0.153-0.156 nm in the neutral molecules to 0.19-0.21 nm in the 2 A 1 and 2 A g states of the radical cations, respectively [10,52].…”

mentioning

confidence: 99%