Substituent Effects on the Reactivity of the 2,4,6-Tridehydropyridinium Cation, an Aromatic σ,σ,σ-Triradical

Jinshan Gao, Bartłomiej J. Jankiewicz, Huaming Sheng, Lindsey Kirkpatrick, Xin Ma, John J. Nash, Hilkka I. Kenttämaa

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

2,4,6-Tridehydropyridinium cation (7) undergoes three consecutive atom or atom group abstractions from reagent molecules in the gas phase. By placing a π-electron-donating hydroxyl group between two radical sites, their reactivity can be quenched by enhancing their through-space coupling via a favorable resonance structure. Indeed, 3-hydroxy-2,4,6-tridehydropyridinium cation (8) abstracts only one atom or group of atoms from reagents. On the other hand, an electron-withdrawing cyano group between two of the radical sites (9) destabilizes the analogous resonance structure and diminishes through-space coupling between the radical sites, resulting in abstraction of three atoms, just like 7. However, the cyano-substituent also increases acidity to the point that 9 reacts predominantly via proton transfer instead of undergoing radical reactions. Therefore, acidic triradicals may undergo nonradical, barrierless proton transfer reactions faster than radical reactions, which are usually accompanied by barriers. Examination of the analogous cyano-substituted mono- and biradicals revealed behavior similar to that of the corresponding unsubstituted species, with the exception of substantially greater reactivities due to their greater (calculated) vertical electron affinities. Finally, the 3-cyano-2,6-didehydropyridinium cation with a singlet ground state (S-T splitting: –11.9 kcal mol–1) was found to react exclusively from the lowest-energy triplet state by fast proton transfer reactions.

Original languageEnglish
Pages (from-to)6582-6589
Number of pages8
JournalEuropean Journal of Organic Chemistry
Volume2018
Issue number46
DOIs
StatePublished - 13 Dec 2018

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Cations
reactivity
Proton transfer
cations
Atoms
atoms
reagents
protons
Electron affinity
Electrons
electron affinity
Acidity
acidity
Hydroxyl Radical
Electron energy levels
Ground state
atomic energy levels
electrons
examination
Gases

Keywords

  • Acidity
  • Cations
  • Radical reactions
  • Reactivity
  • Substituent effects

Cite this

Gao, Jinshan ; Jankiewicz, Bartłomiej J. ; Sheng, Huaming ; Kirkpatrick, Lindsey ; Ma, Xin ; Nash, John J. ; Kenttämaa, Hilkka I. / Substituent Effects on the Reactivity of the 2,4,6-Tridehydropyridinium Cation, an Aromatic σ,σ,σ-Triradical. In: European Journal of Organic Chemistry. 2018 ; Vol. 2018, No. 46. pp. 6582-6589.
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abstract = "2,4,6-Tridehydropyridinium cation (7) undergoes three consecutive atom or atom group abstractions from reagent molecules in the gas phase. By placing a π-electron-donating hydroxyl group between two radical sites, their reactivity can be quenched by enhancing their through-space coupling via a favorable resonance structure. Indeed, 3-hydroxy-2,4,6-tridehydropyridinium cation (8) abstracts only one atom or group of atoms from reagents. On the other hand, an electron-withdrawing cyano group between two of the radical sites (9) destabilizes the analogous resonance structure and diminishes through-space coupling between the radical sites, resulting in abstraction of three atoms, just like 7. However, the cyano-substituent also increases acidity to the point that 9 reacts predominantly via proton transfer instead of undergoing radical reactions. Therefore, acidic triradicals may undergo nonradical, barrierless proton transfer reactions faster than radical reactions, which are usually accompanied by barriers. Examination of the analogous cyano-substituted mono- and biradicals revealed behavior similar to that of the corresponding unsubstituted species, with the exception of substantially greater reactivities due to their greater (calculated) vertical electron affinities. Finally, the 3-cyano-2,6-didehydropyridinium cation with a singlet ground state (S-T splitting: –11.9 kcal mol–1) was found to react exclusively from the lowest-energy triplet state by fast proton transfer reactions.",
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Substituent Effects on the Reactivity of the 2,4,6-Tridehydropyridinium Cation, an Aromatic σ,σ,σ-Triradical. / Gao, Jinshan; Jankiewicz, Bartłomiej J.; Sheng, Huaming; Kirkpatrick, Lindsey; Ma, Xin; Nash, John J.; Kenttämaa, Hilkka I.

In: European Journal of Organic Chemistry, Vol. 2018, No. 46, 13.12.2018, p. 6582-6589.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Substituent Effects on the Reactivity of the 2,4,6-Tridehydropyridinium Cation, an Aromatic σ,σ,σ-Triradical

AU - Gao, Jinshan

AU - Jankiewicz, Bartłomiej J.

AU - Sheng, Huaming

AU - Kirkpatrick, Lindsey

AU - Ma, Xin

AU - Nash, John J.

AU - Kenttämaa, Hilkka I.

PY - 2018/12/13

Y1 - 2018/12/13

N2 - 2,4,6-Tridehydropyridinium cation (7) undergoes three consecutive atom or atom group abstractions from reagent molecules in the gas phase. By placing a π-electron-donating hydroxyl group between two radical sites, their reactivity can be quenched by enhancing their through-space coupling via a favorable resonance structure. Indeed, 3-hydroxy-2,4,6-tridehydropyridinium cation (8) abstracts only one atom or group of atoms from reagents. On the other hand, an electron-withdrawing cyano group between two of the radical sites (9) destabilizes the analogous resonance structure and diminishes through-space coupling between the radical sites, resulting in abstraction of three atoms, just like 7. However, the cyano-substituent also increases acidity to the point that 9 reacts predominantly via proton transfer instead of undergoing radical reactions. Therefore, acidic triradicals may undergo nonradical, barrierless proton transfer reactions faster than radical reactions, which are usually accompanied by barriers. Examination of the analogous cyano-substituted mono- and biradicals revealed behavior similar to that of the corresponding unsubstituted species, with the exception of substantially greater reactivities due to their greater (calculated) vertical electron affinities. Finally, the 3-cyano-2,6-didehydropyridinium cation with a singlet ground state (S-T splitting: –11.9 kcal mol–1) was found to react exclusively from the lowest-energy triplet state by fast proton transfer reactions.

AB - 2,4,6-Tridehydropyridinium cation (7) undergoes three consecutive atom or atom group abstractions from reagent molecules in the gas phase. By placing a π-electron-donating hydroxyl group between two radical sites, their reactivity can be quenched by enhancing their through-space coupling via a favorable resonance structure. Indeed, 3-hydroxy-2,4,6-tridehydropyridinium cation (8) abstracts only one atom or group of atoms from reagents. On the other hand, an electron-withdrawing cyano group between two of the radical sites (9) destabilizes the analogous resonance structure and diminishes through-space coupling between the radical sites, resulting in abstraction of three atoms, just like 7. However, the cyano-substituent also increases acidity to the point that 9 reacts predominantly via proton transfer instead of undergoing radical reactions. Therefore, acidic triradicals may undergo nonradical, barrierless proton transfer reactions faster than radical reactions, which are usually accompanied by barriers. Examination of the analogous cyano-substituted mono- and biradicals revealed behavior similar to that of the corresponding unsubstituted species, with the exception of substantially greater reactivities due to their greater (calculated) vertical electron affinities. Finally, the 3-cyano-2,6-didehydropyridinium cation with a singlet ground state (S-T splitting: –11.9 kcal mol–1) was found to react exclusively from the lowest-energy triplet state by fast proton transfer reactions.

KW - Acidity

KW - Cations

KW - Radical reactions

KW - Reactivity

KW - Substituent effects

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