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

Wittrig, Ashley M.; Archibold, Enada; Sheng, Huaming; Nash, John J.; Kenttämaa, Hilkka I.

doi:10.1016/j.ijms.2014.04.017

Cited by 8 publications

(11 citation statements)

References 29 publications

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“…[e] URI=unreactive isomer; the CAD processes used to generate these biradicals also yield isomeric enediynes that are unreactive (ref. ).…”

Section: Resultsmentioning

confidence: 97%

“…Third, ion activation in ISCAD only involves a few activating collisions, whereas ions undergo a very large number of collisions in CAD ion traps, each of which deposits only a small amount of internal energy into the ions until the activation threshold has been reached. This process often leads to rearrangement reactions . Therefore, ISCAD was used in this study to test whether the formation of the highly reactive, unknown biradical requires several activation steps as in ITCAD, or whether it can be generated in just a few steps by using ISCAD.…”

Section: Resultsmentioning

confidence: 99%

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Relative Reactivities of Three Isomeric Aromatic Biradicals with a 1,4‐Biradical Topology Are Controlled by Polar Effects

Jin

Wang

et al. 2019

Chemistry A European J

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Unexpectedly, the 5‐dehydroquinoline radical cation was formed in the gas phase from the 5‐iodo‐8‐nitroquinolinium cation upon ion‐trap collision‐activated dissociation. This reaction involves the cleavage of a nitro group to generate an intermediate monoradical, namely, the 8‐dehydro‐5‐iodoquinolinium cation, followed by rearrangement through abstraction of a hydrogen atom from the protonated nitrogen atom by the radical site. Dissociation of the rearranged radical cation through elimination of an iodine atom generates the 5‐dehydroquinoline radical cation. The mechanism was probed by studying isomeric biradicals and performing quantum chemical calculations. The 5‐dehydroquinoline radical cation showed greater gas‐phase reactivity toward dimethyl disulfide, cyclohexane, and allyl iodide than the isomeric 5,8‐didehydroquinolinium cation, which is more reactive than the isomeric 5,8‐didehydroisoquinolinium cation studied previously. All three isomers have a 1,4‐biradical topology. The order of reactivity is rationalized by the vertical electron affinities of the radical sites of these biradicals instead of their widely differing singlet–triplet splittings.

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“…[e] URI=unreactive isomer; the CAD processes used to generate these biradicals also yield isomeric enediynes that are unreactive (ref. ).…”

Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Relative Reactivities of Three Isomeric Aromatic Biradicals with a 1,4‐Biradical Topology Are Controlled by Polar Effects

Jin

Wang

et al. 2019

Chemistry A European J

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“…The greater the EA v , the more polar the transition state, and the lower its energy . Previous calculations suggest that the EA v of analogous monoradicals with the radical site at the 2‐position is larger than for radicals with the radical site at the 3‐position, thus leading to greater reactivity . The cyano‐substituent increases the reactivity of all these radicals when compared to their unsubstituted counterparts by increasing their EA v (Table ).…”

Section: Figurementioning

confidence: 95%

“…Attaching a charged moiety to a reaction intermediate of interest (the “distonic ion approach”) has been successfully utilized to characterize the gas‐phase reactivity of several meta ‐benzynes in mass spectrometers. In a recent study, two para ‐benzyne analogs with different skeletons, the 5,8‐didehydroisoquinolinium cation and the 2,5‐didehydropyridinium cation ( 1 , Figure ), were successfully generated in a dual‐linear quadrupole ion trap mass spectrometer and their gas‐phase reactivity toward several reagents was studied. The more polar biradical 1 (with the greater calculated vertical electron affinity (EA v ) of the radical sites; 6.76 vs. 5.32 eV; calculated at the RHF‐BCCD(T)/cc‐pVTZ//UB3LYP/cc‐pVTZ level of theory) was found to be more reactive, in spite of its greater S−T splitting (−4.6 vs. −3.7 kcal mol −1 , same level of theory).…”

Section: Figurementioning

confidence: 99%

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Polar Effects Control the Gas‐Phase Reactivity of para‐Benzyne Analogs

Sheng

Lei

et al. 2018

ChemPhysChem

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We report herein a gas-phase reactivity study on a para-benzyne cation and its three cyano-substituted, isomeric derivatives performed using a dual-linear quadrupole ion trap mass spectrometer. All four biradicals were found to undergo primary and secondary radical reactions analogous to those observed for the related monoradicals, indicating the presence of two reactive radical sites. The reactivity of all biradicals is substantially lower than that of the related monoradicals, as expected based on the singlet ground states of the biradicals. The cyano-substituted biradicals show substantially greater reactivity than the analogous unsubstituted biradical. The greater reactivity is rationalized by the substantially greater (calculated) electron affinity of the radical sites of the cyano-substituted biradicals, which results in stabilization of their transition states through polar effects. This finding is in contrast to the long-standing thinking that the magnitude of the singlet-triplet splitting controls the reactivity of para-benzynes.

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Reactivity Controlling Factors for an Aromatic Carbon‐Centered σ,σ,σ‐Triradical: The 4,5,8‐Tridehydroisoquinolinium Ion

Vinueza

Jankiewicz

Gallardo

et al. 2015

Chemistry A European J

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The chemical properties of the 4,5,8-tridehydroisoquinolinium ion (doublet ground state) and related mono- and biradicals were examined in the gas phase in a dual-cell Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. The triradical abstracted three hydrogen atoms in a consecutive manner from tetrahydrofuran (THF) and cyclohexane molecules; this demonstrates the presence of three reactive radical sites in this molecule. The high (calculated) electron affinity (EA=6.06 eV) at the radical sites makes the triradical more reactive than two related monoradicals, the 5- and 8-dehydroisoquinolinium ions (EA=4.87 and 5.06 eV, respectively), the reactivity of which is controlled predominantly by polar effects. Calculated triradical stabilization energies predict that the most reactive radical site in the triradical is not position C4, as expected based on the high EA of this radical site, but instead position C5. The latter radical site actually destabilizes the 4,8-biradical moiety, which is singlet coupled. Indeed, experimental reactivity studies show that the radical site at C5 reacts first. This explains why the triradical is not more reactive than the 4-dehydroisoquinolinium ion because the C5 site is the intrinsically least reactive of the three radical sites due to its low EA. Although both EA and spin-spin coupling play major roles in controlling the overall reactivity of the triradical, spin-spin coupling determines the relative reactivity of the three radical sites.

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

Cited by 8 publications

References 29 publications

Relative Reactivities of Three Isomeric Aromatic Biradicals with a 1,4‐Biradical Topology Are Controlled by Polar Effects

Relative Reactivities of Three Isomeric Aromatic Biradicals with a 1,4‐Biradical Topology Are Controlled by Polar Effects

Polar Effects Control the Gas‐Phase Reactivity of para‐Benzyne Analogs

Reactivity Controlling Factors for an Aromatic Carbon‐Centered σ,σ,σ‐Triradical: The 4,5,8‐Tridehydroisoquinolinium Ion

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