Electronic Absorption Spectra of Some Alkoxyl Radicals. An Experimental and Theoretical Study

Avila, D. V.; Ingold, K. U.; Nardo, Ariel A. Di; Zerbetto, Francesco; Zgierski, Marek Z.; Lusztyk, J.

doi:10.1021/ja00115a005

Cited by 81 publications

(118 citation statements)

References 2 publications

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“…In acetonitrile solution, CumOc is characterized by an absorption band in the visible region of the spectrum centered at 485 nm. 32,33 Under these conditions, CumOc decays mainly by C-CH 3 b-scission. 33,34 Previous studies have shown the stability of dicumyl peroxide in AcOH solution.…”

Section: Resultsmentioning

confidence: 97%

“…The observed rate constants (k obs ) were obtained by averaging 2-5 individual values and were reproducible to within 5%. On the basis of the change in absorbance observed aer laser excitation at the CumOc visible absorption band maximum (l max ¼ 485 nm), and the CumOc extinction coefficient, 32 the amount of peroxide that dissociates upon laser excitation can be estimated as <1%.…”

Section: Methodsmentioning

confidence: 99%

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Tuning hydrogen atom abstraction from the aliphatic C–H bonds of basic substrates by protonation. Control over selectivity by C–H deactivation

2013

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A kinetic study on the effect of acetic (AcOH) and trifluoroacetic acid (TFA) on hydrogen abstractions from the C-H bonds of basic substrates by the cumyloxyl radical (CumOc) was carried out in acetonitrile. With tetrahydropyran no significant effect on k H was observed after acid addition. With the more basic tertiary amines acid addition led to greater than 4-orders of magnitude decreases in k H . Protonation at nitrogen decreases the degree of overlap between the a-C-H s* orbital and the lone-pair leading to an increase in the strength of the C-H bond and a destabilization of the radical formed after abstraction.Evidence that C-H deactivation extends up to the g-C-H bonds and for the reversibility of this approach was also provided. With TFA no reaction was observed up to [amine] ¼ [TFA], pointing towards stoichiometric protonation. At [amine] > [TFA], k H values that are very similar to those measured in the absence of added acid were obtained. With the weaker acid, AcOH, no reaction was observed up to[AcOH]/[amine] $4, and a curved plot was observed with increasing [amine], as a result of the acidbase equilibrium between AcOH and the amine. With 1,4-dimethylpiperazine, a quantitative evaluation of the C-H deactivation determined by sequential protonation of one or both nitrogen centers was obtained. These observations show that protonation provides an extremely efficient, precise and tunable method for the deactivation of the C-H bonds of basic substrates allowing moreover for careful control over the hydrogen abstraction selectivity. The implications of this approach are discussed.

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Section: Resultsmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 99%

Tuning hydrogen atom abstraction from the aliphatic C–H bonds of basic substrates by protonation. Control over selectivity by C–H deactivation

2013

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“…15 This hydrogen atom abstraction reaction occurs in competition with the β-scission of CumO • , which leads to the formation of acetophenone and a methyl radical (eq 3 in Scheme 2; k β ∼ 6.5 × 10 5 s −1 in CH 3 CN). 13 Figure 5 shows the time-resolved spectra obtained. The first-order decay of the cumyloxyl radical recorded at its maximal absorption wavelength (485 nm) 14 is accompanied by the buildup of the QINO absorption at 390 nm.…”

Section: ■ Resultsmentioning

confidence: 99%

Hydrogen Atom Transfer (HAT) Processes Promoted by the Quinolinimide-N-oxyl Radical. A Kinetic and Theoretical Study

et al. 2017

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A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of organic compounds to the quinolinimide-N-oxyl radical (QINO) was performed in CH 3 CN. The HAT rate constants are significantly higher than those observed with the phthalimide-N-oxyl radical (PINO) as a result of enthalpic and polar effects due to the presence of the Nheteroaromatic ring in QINO. The relevance of polar effects is supported by theoretical calculations conducted for the reactions of the two N-oxyl radicals with toluene, which indicate that the HAT process is characterized by a significant degree of charge transfer permitted by the π-stacking that occurs between the toluene and the N-oxyl aromatic rings in the transition state structures. An increase in the HAT reactivity of QINO was observed in the presence of 0.15 M HClO 4 and 0.15 M Mg(ClO 4 ) 2 due to the protonation or complexation with the Lewis acid of the pyridine nitrogen that leads to a further decrease in the electron density in the N-oxyl radical. These results fully support the use of N-hydroxyquinolinimide as a convenient substitute for N-hydroxyphthalimide in the catalytic aerobic oxidations of aliphatic hydrocarbons characterized by relatively high C−H bond dissociation energies.

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“…3). Since the phenyl group in benzyloxyl radicals favors co-planar alignment of aromatic plane and radical oxygen, 46 axial phenyl, and exo-bisectional vinyl group orientation lead to no significant steric repulsion (Fig. 3, bottom right).…”

Section: Intramolecular Additionmentioning

confidence: 99%

Tertiary alkoxyl radicals from 3-alkoxythiazole-2(3H)-thiones

Schur¹,

Becker²,

Bergsträßer³

et al. 2011

Tetrahedron

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Electronic Absorption Spectra of Some Alkoxyl Radicals. An Experimental and Theoretical Study

Cited by 81 publications

References 2 publications

Tuning hydrogen atom abstraction from the aliphatic C–H bonds of basic substrates by protonation. Control over selectivity by C–H deactivation

Tuning hydrogen atom abstraction from the aliphatic C–H bonds of basic substrates by protonation. Control over selectivity by C–H deactivation

Hydrogen Atom Transfer (HAT) Processes Promoted by the Quinolinimide-N-oxyl Radical. A Kinetic and Theoretical Study

Tertiary alkoxyl radicals from 3-alkoxythiazole-2(3H)-thiones

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