Radical Reactions of Didehydroarenes with a 1,4-Relationship

Amegayibor, F. Sedinam; Nash, John J.; Kenttämaa, Hilkka I.

doi:10.1021/ja0360079

Cited by 17 publications

(27 citation statements)

References 26 publications

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“…1.6 Å; Figure 1). Therefore, even though the S-T gaps and EAs (6.30, 6.50, and 6.59 eV, respectively 15 ) of b-d are similar, their structural differences may lead to very different reactivities; that is, biradicals b and d might undergo electrophilic addition reactions, while c may display reactivity that is more radical-like.A well-known 8,9,11,16 method was used to study the reaction kinetics of b-g in a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer. Their precursors, 3,5-diiodo-, 2-hydroxy-3,5-diiodo-, 17 and 2-chloro-3,5-dinitropyridines, as well as 5,7-dinitro-, 18 8-hydroxy-5,7-diiodo-, and 6,8-dinitroquinolines, 19…”

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Demonstration of Tunable Reactivity for meta-Benzynes

et al. 2005

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A combined computational and experimental study on the gas-phase structures and reactivities of charged 1,3-didehydroarenes (meta-benzynes) demonstrates that the reactivity of such biradicals can be "tuned" by using appropriate substituents. Substituents that destabilize a specific zwitterionic resonance structure can change the reactivity of the biradical from mildly carbocationic to radical-like. These substituent effects are not the result of changes in the singlet-triplet gaps of the biradicals, but rather reflect changes in the potential energy surfaces for the dehydrocarbon separation.

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Demonstration of Tunable Reactivity for meta-Benzynes

et al. 2005

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“…The calculated S-T gaps and EAs for the biradicals are given in Table 1. Previously published studies [9,11] have demonstrated that the biradicals 1 and 2 react exclusively via radical pathways, while radical 3 undergoes electrophilic addition/elimination reactions. The results for the reactions of the (bi)radicals with the various sugars are summarized in Tables 2 and 3.…”

Section: Reactivity Studiesmentioning

confidence: 99%

“…It was demonstrated in a recent study [11] that as the EA of a biradical increases, the overall reaction efficiency increases for reactions with simple organic substrates. The ordering of the EAs for the biradicals studied here (1a Ͼ 1b Ͼ 2a Ͼ 2b Ͼ 3a Ͼ 3b; Table 1) correlates to some extent with the relative reaction efficiencies for the sugars.…”

Section: Polar Effectsmentioning

confidence: 99%

“…Biradicals with large S-T gaps appear to avoid this penalty by undergoing nucleophilic or electrophilic (nonradical) addition reactions [10]. Recent gas-phase studies have shown that in addition to S-T gap effects [9], reactions of biradicals with simple organic substrates are also sensitive to polar effects (which is reflected by the biradical's calculated vertical electron affinity, EA) [11]. Here, we report an examination of the reactivity of several ,-biradicals (Scheme 1) toward various sugars, and show that these reactions are also affected by the S-T gap and the EA of the biradical.…”

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Reactivity of aromatic σ,σ-biradicals toward riboses

Adeuya

Yang

Amegayibor

et al. 2006

J. Am. Soc. Mass Spectrom.

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The gas-phase reactions of sugars with aromatic, carbon-centered ,-biradicals with varying polarities [as reflected by their calculated electron affinities (EA)] and extent of spin-spin coupling [as reflected by their calculated singlet-triplet (S-T) gaps] have been studied. The biradicals are positively charged, which allows them to be manipulated and their reactions to be studied in a Fourier-transform ion cyclotron resonance mass spectrometer. Hydrogen atom abstraction from sugars was found to be the dominant reaction for the biradicals with large EA values, while the biradicals with large S-T gaps tend to form addition/elimination products instead. Hence, not all ,-biradicals may be able to damage DNA by hydrogen atom abstraction. The overall reaction efficiencies of the biradicals towards a given substrate were found to be directly related to the magnitude of their EA values, and inversely related to their S-T gaps. The EA of a biradical appears to be a very important rate-controlling factor, and it may even counterbalance the reduced radical reactivity characteristic of singlet biradicals that have large S-T gaps. . These intermediates are believed to irreversibly damage double-stranded DNA via hydrogen atom abstraction from a sugar moiety in each strand [2]. Therefore, a better understanding of the factors controlling the reactivity of these biradicals toward sugars is important.Solution [3] and gas-phase [4] studies on the reactivity of neutral and charged phenyl radicals have confirmed that these monoradicals can abstract hydrogen atoms from sugars as well as from the sugar moiety in nucleosides and dinucleoside phosphates. Polar effects (i.e., polarization of the transition state) play a major role in controlling these reactions [5][6][7]. However, no such studies have been reported for the analogous biradicals.The magnitude of the singlet-triplet (S-T) gap has been proposed earlier [8] as the major reaction rate controlling factor for aromatic ,-biradicals with singlet ground states. As the magnitude of the S-T gap increases, the reaction efficiency for hydrogen atom abstraction from simple substrates has been observed to decrease, presumably because of the energetically high cost of uncoupling the biradical's electrons in the transition state [8,9]. Biradicals with large S-T gaps appear to avoid this penalty by undergoing nucleophilic or electrophilic (nonradical) addition reactions [10]. Recent gas-phase studies have shown that in addition to S-T gap effects [9], reactions of biradicals with simple organic substrates are also sensitive to polar effects (which is reflected by the biradical's calculated vertical electron affinity, EA) [11]. Here, we report an examination of the reactivity of several ,-biradicals (Scheme 1) toward various sugars, and show that these reactions are also affected by the S-T gap and the EA of the biradical.

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“…Dimethyl disulfide and a variety of hydrogen atom donors, such as 1,4-cyclohexadiene and thiophenol, are often used since positively charged radicals react with dimethyl disulfide by thiomethyl radical abstraction and with hydrogen donors by hydrogen atom abstraction [23, 24, 26, 30, 31]. Two sequential atom or group abstractions have been reported for biradicals [30,31]. Therefore, the ion of interest was allowed to react with dimethyl disulfide and selected hydrogen atom donors.…”

Section: Resultsmentioning

confidence: 99%

Generation and Characterization of a Distonic Biradical Anion Formed from an Enediynone Prodrug in the Gas Phase

Yang

Bekele

Lipton

et al. 2013

J. Am. Soc. Mass Spectrom.

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A negatively charged biradical intermediate was successfully generated in the gas phase via cyclization of the deprotonated bicyclo[8.3.0]trideca-12-ene-2,7-diyn-1-one precursor. The inherent negative charge of this biradical allows its characterization via collision-activated dissociation and reactions with a variety of neutral substrates in an FT-ICR mass spectrometer. Although the biradical is unreactive toward reagents that usually react rapidly with positively charged biradicals, such as dimethyl disulfide, it reacts with the halogen-containing substrates carbon tetrachloride, carbon tetrabromide and bromotrichloromethane via bromine or chlorine atom abstraction, which supports its biradical structure. The results presented in this study indicate that cyclizations commonly used in solution to form biradical intermediates from enediyne compounds may also occur in the gas phase.

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Radical Reactions of Didehydroarenes with a 1,4-Relationship

Abstract: A gas-phase study of the radical reactivities of didehydroarenes with a 1,4-relationship reveals that electronic effects (due to singlet-triplet state splittings) can be offset by polar effects.

Cited by 17 publications

References 26 publications

Demonstration of Tunable Reactivity for meta-Benzynes

Demonstration of Tunable Reactivity for meta-Benzynes

Reactivity of aromatic σ,σ-biradicals toward riboses

Generation and Characterization of a Distonic Biradical Anion Formed from an Enediynone Prodrug in the Gas Phase

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