Intramolecular electron exchange in the 2,7-dinitronaphthalene radical anion : electron paramagnetic resonance and kinetic data

Telo, João P.; Shohoji, M. Cândida B. L.; Herold, Bernardo J.; Grampp, Günter

doi:10.1039/ft9928800047

Cited by 33 publications

(27 citation statements)

References 9 publications

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“…Dinitroaromatic radical anions have been the subject of our studies on MV chemistry for the last several years . A wide range of properties can be achieved by changing the nature of the aromatic bridge on these radicals.…”

Section: Introductionmentioning

confidence: 99%

“…Decreasing the conjugation (and hence H ab ) by the twisting around the central bond on substituted biphenyl bridges, as in 2,2′‐dimethyl‐4,4′‐dinitrobiphenyl radical anion, also leads to localization of charge . Dinitroaromatic radical anions with non‐Kekulé substitution patterns like 1,3‐dinitrobenzene, 2,7‐dinitronaphthalene, or 2,7‐dinitrodibenzodioxin radical anions have small enough H ab values to make them localized Class II radicals in all solvents studied …”

Section: Introductionmentioning

confidence: 99%

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Dicyanoaromatic radical anions as mixed valence species

Moneo

Carvalho

Telo

2012

J of Physical Organic Chem

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The reduction of nine symmetric dicyanoaromatic radical anions by sodium amalgam in the presence of cryptand[2.2.2] was studied using cyclic voltammetry and using optical and electron paramagnetic resonance (EPR) spectroscopies in two aprotic solvents. All radicals are charge‐delocalized (Class III) mixed valence species, as shown by the weak solvatochromism of their low‐energy optical bands and by the vibrational structure exhibited by most of the bands. The maximum of the low‐energy optical transition decreases logarithmically with the number of bonds (n) between cyano groups in a series of p‐phenylene‐bridged radicals, from p‐phenyl (n = 5) to p‐quaterphenyl (n = 17), although the energy of the latter lies higher than the value predicted by the linear regression. The energy of this band decreases linearly with the cos2 value of the torsion angle between phenyl rings in the spectra of biphenyl‐4,4′‐dicarbonitrile radical anion and their methyl‐substituted derivatives. The fact that charge delocalization is maintained in radicals with non‐Kekulé bridges, with unusually large bridges and with bridges with highly twisted biphenyl systems suggests that cyano charge‐bearing units have small reorganization energies and induce high electronic couplings through the bridges. Copyright © 2012 John Wiley & Sons, Ltd.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dicyanoaromatic radical anions as mixed valence species

Moneo

Carvalho

Telo

2012

J of Physical Organic Chem

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“…It is usually believed that the absence of direct resonance between the donor and the acceptor is necessary for the occurrence of alternating line-broadening effects caused by IEE in the EPR spectra of free radicals. The examples known in the literature, where the two groups are either in nonconjugative meta positions, as in the radical anions of 1,3-dinitrobenzene and 2,7-dinitronaphthalene [351], or sterically forced out of planarity, as in the radical anion of dinitrodurene [352], seems to confirm this behavior. Line broadening effects due to intramolecular electron exchange are recently observed in the EPR spectra of 2,6-dinitrophenolate radical dianion, where the resonance structures can be drawn delocalizing the electron through the two nitro groups [353].…”

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confidence: 57%

“…In radical anions of 1,3-dinitrobenzenes [318] and 2,7-dinitronaphthalene [319] in protic solvents, the strong solvation of one nitro group through hydrogen bonding causes an asymmetric distribution of the spin densities on the nitrogen atoms, inducing slow intramolecular electron exchange between the two nitro groups. The rate constants determined from line broadening effects are in the fast region range ( K = lo9 s-') in aprotic solvents while in alcohols the exchange is slow ( K z lo6 s-') on the EPR time scale [318,319]. The position of the OH group is a decisive factor in the variation of the rate constant with the deprotonation of the radical anion, variation being large when the OH group is in the ortho position to one nitro group.…”

Section: R = H Hexylmentioning

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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“…used the direct‐COSMO‐RS (conductor‐like screening model for real solvents) model in combination with the time‐dependent density functional theory method . Although these studies successfully reproduced the experimental observation that the free energy barrier in MeOH is much higher than that in MeCN, they provide little information on the dynamical aspects of the ET in solution. Furthermore, the one‐dimensional model does not explicitly treat the intramolecular modes.…”

Section: Introductionmentioning

confidence: 99%

Computational study on intramolecular electron transfer in 1,3-dintrobenzene radical anion

Mori

2014

J. Phys. Org. Chem.

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1,3‐Dinitrobenzene radical anion (DNB−), which is a typical mixed valence compound, undergoes intramolecular electron transfer (ET) in solution. It is reported that the ET rates exceed 1010 s−1 in polar aprotic solvent such as acetonitrile. Formulation based on a simple one‐dimensional model cannot quantitatively account for the observed ET rates, and further study has been desired for better understanding of the solvent effects on the ET. In the present study, molecular dynamics simulations were performed for DNB− in the vacuum and in acetonitrile solution. In the vacuum, ET was induced by the antisymmetric C–N stretching mode on a timescale of ~100 fs, and the charge transferring between the nitro groups was much less than unity. For the acetonitrile solution, short‐timescale and long‐timescale simulations were performed using a droplet model of solvated DNB− at 298 K. Although the mean C–N distance in the charged nitro group was longer than that in the vacuum, no ET took place in the short (~150 fs) simulations. The solvent coordinate, which was defined as the difference in the solute–solvent interaction energy between the reactant and the product, significantly fluctuated even in short‐time simulations. The reorganization energies in acetonitrile were evaluated on the basis of molecular orbital (MO) calculations, and the ratio of the inner sphere and outer sphere parts, λi/λo, was estimated to be ~0.6. The results suggest that the intramolecular mode and fast solvent mode may play an important role in the present ET reaction. Copyright © 2014 John Wiley & Sons, Ltd.

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Intramolecular electron exchange in the 2,7-dinitronaphthalene radical anion : electron paramagnetic resonance and kinetic data

Cited by 33 publications

References 9 publications

Dicyanoaromatic radical anions as mixed valence species

Dicyanoaromatic radical anions as mixed valence species

Electron‐transfer Reactions of Aromatic Compounds

Computational study on intramolecular electron transfer in 1,3-dintrobenzene radical anion

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