Reactivity of the 3,4,5‐Tridehydropyridinium Cation—An Aromatic σ,σ,σ‐Triradical

Jankiewicz, Bartłomiej J.; Reece, Jennifer N.; Vinueza, Nelson R.; Nash, John J.; Kenttämaa, Hilkka I.

doi:10.1002/ange.200802714

Cited by 12 publications

(5 citation statements)

References 43 publications

(35 reference statements)

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“…This was expected as previous studies have demonstrated that thiomethyl abstraction is a dominant reaction for many related charged mono-and biradicals (distonic ions). 5,11,12,35 Only a small amount of DMDS radical cation (1−14% relative abundance; Table 1) was observed. In sharp contrast, the four isomeric triradicals studied (4−7; Table 1) produce the DMDS radical cation as the major product (83−94% relative abundance; Table 1).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Quinoline Triradicals: A Reactivity Study

et al. 2019

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The gas-phase reactivities of several protonated quinoline-based σ-type (carbon-centered) mono-, bi-, and triradicals toward dimethyl disulfide (DMDS) were studied by using a linear quadrupole ion trap mass spectrometer. The mono- and biradicals produce abundant thiomethyl abstraction products and small amounts of DMDS radical cation, as expected. Surprisingly, all triradicals produce very abundant DMDS radical cations. A single-step mechanism involving electron transfer from DMDS to the triradicals is highly unlikely because the (experimental) adiabatic ionization energy of DMDS is almost 3 eV greater than the (calculated) adiabatic electron affinities of the triradicals. The unexpected reactivity can be explained based on an unprecedented two-step mechanism wherein the protonated triradical first transfers a proton to DMDS, which is then followed by hydrogen atom abstraction from the protonated sulfur atom in DMDS by the radical site in the benzene ring of the deprotonated triradical to generate the conventional DMDS radical cation and a neutral biradical. Quantum chemical calculations as well as examination of deuterated and methylated triradicals provide support for this mechanism. The proton affinities of the neutral triradicals (and DMDS) influence the first step of the reaction while the vertical electron affinities and spin–spin coupling of the neutral triradicals influence the second step. The calculated total reaction exothermicities for the triradicals studied range from 27.6 up to 29.9 kcal mol–1.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Quinoline Triradicals: A Reactivity Study

et al. 2019

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“…Monoradicals 5 , 6 , 7 , and 8 show major reaction products, with branching ratios at or near 100%, that are diagnostic [21] for the presence of a radical site, such as a H atom abstraction product for cyclohexane and tetrahydrofuran, I atom abstraction product for allyl iodide and SCH 3 abstraction product for dimethyl disulfide (see Tables 1 and 2). The same primary reactions were observed for the para -benzynes.…”

Section: Resultsmentioning

confidence: 99%

Polar effects control the gas-phase reactivity of charged para-benzyne analogs

Wittrig

Archibold

Sheng

et al. 2015

International Journal of Mass Spectrometry

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The gas-phase reactivity of charged para-benzynes is entirely unexplored as they and/or their precursors tend to undergo ring-opening upon their generation. We report here a gas-phase reactivity study of two such benzynes, the 2,5-didehydropyridinium and 5,8-didehydroisoquinolinium cations, generated in a modified dual-linear quadrupole ion trap (DLQIT) mass spectrometer. Both biradicals were found to form diagnostic products with organic molecules, indicating the presence of two radical sites. As opposed to earlier predictions that the singlet-triplet (S-T) splitting controls the radical reactivity of such species, the 2,5-didehydropyridinium cation reacts much faster in spite of its larger S-T splitting. Calculated vertical electron affinities of the radical sites of the para-benzynes, a parameter related to the polarity of the transition states of their reactions, appears to be the most important reactivity controlling factor.

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“…To gain additional insight into the hydrogen atom abstraction reactions of 8, another hydrogen atom donor, cyclohexane, was examined. In a previous study, [16] mono-and biradicals were found to react with cyclohexane solely by one and/or two hydrogen atom abstractions. Biradical 8 reacts with cyclohexane by addition (19 %), and by one (35 %) as well as two (46 %) hydrogen atom abstractions (Scheme 7; reaction efficiency = 18 %).…”

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confidence: 91%

“…[4b, 6] Instead, 11 behaves like an activated electrophilic alkyne and readily undergoes nonradical addition reactions, as observed in previous studies. [16] The main reactions of 11 with THF (CH 2 O abstraction (49 %) and H 2 O abstraction (36 %)), AI (addition (72 %)), DMDS (HSCH 3 abstraction (92 %)), and tBuNC (HCN abstraction (90 %)), are thought to occur via nonradical mechanisms and hence do not require uncoupling of the biradical electrons in the transition state. [16] Therefore, they are not expected to be dependent on the magnitude of DE ST .…”

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confidence: 99%

“…[16] The main reactions of 11 with THF (CH 2 O abstraction (49 %) and H 2 O abstraction (36 %)), AI (addition (72 %)), DMDS (HSCH 3 abstraction (92 %)), and tBuNC (HCN abstraction (90 %)), are thought to occur via nonradical mechanisms and hence do not require uncoupling of the biradical electrons in the transition state. [16] Therefore, they are not expected to be dependent on the magnitude of DE ST . Comparison of the reactivity of biradical 8 to that of bi-A C H T U N G T R E N N U N G radicals 11 and 12 and monoradicals 9 and 10 reveals that almost all the product ions formed for 8, but not for 9, 10, or 12, are also formed for biradical 11.…”

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Reactivity of the 4,5‐Didehydroisoquinolinium Cation

Vinueza¹,

Archibold²,

Jankiewicz³

et al. 2012

Chemistry A European J

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The chemical properties of a 1,8-didehydronaphthalene derivative, the 4,5-didehydroisoquinolinium cation, were examined in the gas phase in a dual-cell Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. This is an interesting biradical because it has two radical sites in close proximity, yet their coupling is very weak. In fact, the biradical is calculated to have approximately degenerate singlet and triplet states. This biradical was found to exclusively undergo radical reactions, as opposed to other related biradicals with nearby radical sites. The first bond formation occurs at the radical site in the 4-position, followed by that in the 5-position. The proximity of the radical sites leads to reactions that have not been observed for related mono- or biradicals. Interestingly, some ortho-benzynes have been found to yield similar products. Since ortho-benzynes do not react via radical mechanisms, these products must be especially favorable thermodynamically.

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Reactivity of the 3,4,5‐Tridehydropyridinium Cation—An Aromatic σ,σ,σ‐Triradical

Cited by 12 publications

References 43 publications

Quinoline Triradicals: A Reactivity Study

Quinoline Triradicals: A Reactivity Study

Polar effects control the gas-phase reactivity of charged para-benzyne analogs

Reactivity of the 4,5‐Didehydroisoquinolinium Cation

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