Picosecond radical kinetics. Rate constants for reaction of benzeneselenol with primary alkyl radicals and calibration of the 6-cyano-5-hexenyl radical cyclization

Newcomb, Martin; Varick, Thomas R.; Ha, Chau; Manek, M. Beata; Yue, Xiaodong

doi:10.1021/ja00047a026

Cited by 63 publications

(42 citation statements)

References 6 publications

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“…The kinetics of ring openings for the series of radicals 1 were determined by an indirect method using Barton's PTOC esters (2) (15) as radical precursors and benzeneselenol trapping as the basis reaction (Scheme 1) (3,(16)(17)(18). The PTOC esters react in radical chain reactions to give acyloxyl radicals (3) that decarboxylate rapidly to give radicals 1.…”

Section: Precursors and Productsmentioning

confidence: 99%

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Picosecond radical kinetics. Rate constants for ring openings of 2-aryl-substituted cyclopropylcarbinyl radicals

Newcomb¹,

Choi²,

Toy³

1999

Can. J. Chem.

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The kinetics of ring openings of a series of eight (trans-2-arylcyclopropyl)methyl radicals (1) were studied by indirect kinetic methods using Barton's PTOC esters as radical precursors and reaction with PhSeH as the competition reaction. The substituents were CF 3 , F, Me, and OMe located on both the para and meta positions of the aromatic ring. Syntheses of the radical precursors and the products of the radical reactions are described. Kinetics were determined between -43 and 25°C in four cases (CF 3 and OMe substituents) and at 0 and 25°C in the other four cases. The rate constants at 25°C ranged from 1.0 × 10 11 s -1 (p-CH 3 ) to 4.1 × 10 11 s -1 (p-CF 3 ). The relatively large acceleration of the p-CF 3 group, ca. 2.5 times as fast as the parent system with Ar = Ph, correlates well with Adam's ∆D substituent parameters but not with other radical substituent parameters. These calibrated radical rearrangements provide a new set of ultrafast reactions that can be applied in mechanistic probe studies.Résumé : On a étudié la cinétique de l'ouverture de cycle d'une série de huit radicaux (trans-2arylcyclopropyl)méthyles (1) à l'aide de méthodes cinétiques indirectes, en utilisant les esters PTOC de Barton comme précurseurs des radicaux et la réaction avec le PhSeH comme réaction en compétition. Des substituants CF 3 , F, Me et OMe ont été placés dans les positions ortho ainsi que méta du noyau aromatique. On décrit les synthèses des précurseurs de radicaux ainsi que celles des produits des réactions radicalaires. Dans quatre cas (substituants CF 3 et OMe), on a déterminé les cinétiques à des températures entre -43 à +25°C et à 0 et 25°C dans les quatre autres cas. Les constantes de vitesse à 25°C vont de 1,0 × 10 11 s -1 (p-CH 3 ) à 4,1 × 10 11 s -1 (p-CF 3 ). L'accélération relativement importante observée avec le groupe p-CF 3 , environ 2,5 fois plus rapide que le système parent dans lequel Ar = Ph, donne une bonne corrélation avec les paramètres de substituants ∆D de Adam, mais ce n'est pas le cas avec les autres paramètres de substituants radicalaires. Ces réarrangements radicalaires calibrés fournissent un nouvel ensemble de réactions ultrarapides qui peuvent être appliquées comme sonde dans des études mécanistiques.

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Section: Precursors and Productsmentioning

confidence: 99%

“…These studies followed the method of Newcomb et al as previously described (4,17). Benzeneselenol, prepared by the method of Foster (30), was distilled under subdued light.…”

Section: Indirect Kinetic Studiesmentioning

confidence: 99%

Picosecond radical kinetics. Rate constants for ring openings of 2-aryl-substituted cyclopropylcarbinyl radicals

Newcomb¹,

Choi²,

Toy³

1999

Can. J. Chem.

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“…Keshan disease) have been observed (Duddeck 1995). Medical treatments of heart diseases and of intoxications by arsenic, cadmium and mercury as well as cancer therapies and the stimulation of the immune system widely use selenium-containing substances (Newcomb et al 1992). The inorganic selenium compounds, e.g.…”

Section: Introductionmentioning

confidence: 99%

Theoretical 1H(Se—H) NMR shifts in meta-substituted Ph—XH (X = O, S, Se)

Sládek¹,

Rottmannová²,

Škorňa³

et al. 2012

Acta Chimica Slovaca

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A systematic comparative theoretical study has been performed on a series of fourteen metasubstituted selenophenols. The optimal geometries were calculated using the density functional theory (DFT) and the Nuclear Magnetic Resonance parameters were computed by applying the Gauge Including Atomic Orbital (GIAO) method. The calculated NMR shifts were correlated with the Hammett constants. The obtained results were also compared with the theoretical data obtained for thiophenols and phenols. Our results indicate the linear dependence between the gas-phase NMR shifts and Hammett constants. However, the presence of large selenium atoms is able to suppress signifi cantly the substituent effect in meta position. Therefore six substituents (Me, OH, MeCO, COOMe, COOEt and CF 3 groups) were excluded from the data evaluation. Correlations with the fundamental stretching vibration frequencies of the mode with the dominant Se-H vibration have not been found.

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“…The N-cyclopropyl MPTP derivatives provide a unique way to probe the mechanism of these benzophenone triplet-mediated oxidations because in direct analogy to the cyclopropylcarbinyl?homoallyl neutral radical rearrangement (Scheme 4), 19 the derived radical cations (if produced) are expected to undergo instantaneous ring opening. Moreover, because the barrier to this ring opening is exceedingly small (vide infra), this process should be competitive with deprotonation of the aminyl radical cation.…”

Section: Introductionmentioning

confidence: 99%

“…20 Electron paramagnetic resonance (EPR) examinations of the radical cation generated from N-cyclopropylamine (11) support this statement. 19 EPR experiments in a solid matrix have provided evidence for the distonic radical cation (ring-opened) structure based upon hyperfine coupling constants and have shown that the aminyl radical cation ring-opens to the distonic radical cation rapidly upon electron removal. 21,22 Subsequent molecular orbital calculations at the MP2 and other levels of theory have suggested that the removal of an electron from N-cyclopropylamine occurs simultaneously with ring opening; the only stable structure is the distonic radical ion, which collapses to a more stable aminopropenyl ion.…”

Section: Introductionmentioning

confidence: 99%

Reaction of benzophenone triplet with aliphatic amines. What a potent neurotoxin can tell us about the reaction mechanism

Grimm

Allen

Finn

et al. 2011

Bioorganic & Medicinal Chemistry

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Picosecond radical kinetics. Rate constants for reaction of benzeneselenol with primary alkyl radicals and calibration of the 6-cyano-5-hexenyl radical cyclization

Cited by 63 publications

References 6 publications

Picosecond radical kinetics. Rate constants for ring openings of 2-aryl-substituted cyclopropylcarbinyl radicals

Picosecond radical kinetics. Rate constants for ring openings of 2-aryl-substituted cyclopropylcarbinyl radicals

Theoretical 1H(Se—H) NMR shifts in meta-substituted Ph—XH (X = O, S, Se)

Reaction of benzophenone triplet with aliphatic amines. What a potent neurotoxin can tell us about the reaction mechanism

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