Use of two‐parameter correlations for studying the radical reactivity of aromatic compounds

Afanas’ev, Igor B.

doi:10.1002/kin.550130207

Cited by 7 publications

(1 citation statement)

References 57 publications

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“…For disubstituted radicals containing either only amino- (20) or only cyano groups (21), three contributing structures can be proposed Thus, stabilisation of these species due to delocalisation would be somewhat weaker than is expected based on the sum of the substituent effects in the monosubstituted analogues.…”

Section: Critical Analysis Of the Existing Approachesmentioning

confidence: 99%

Correlation analysis in the chemistry of free radicals

Cherkasov¹,

Jönsson²,

Галкин³

et al. 2001

Russ. Chem. Rev.

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Published data now available on the use of correlation Published data now available on the use of correlation analysis in free-radical chemistry are discussed systematically. The analysis in free-radical chemistry are discussed systematically. The scales of `radical' scales of `radical' s s-constants of substituents proposed previously -constants of substituents proposed previously are analysed. It is shown that none of them is applicable as a are analysed. It is shown that none of them is applicable as a general scale because almost in all cases, it is impossible to general scale because almost in all cases, it is impossible to separate correctly the proper radical and polar contributions to separate correctly the proper radical and polar contributions to the overall effect of substituents. A new approach to the quanti-the overall effect of substituents. A new approach to the quantitative estimation of the relationship between the structure and tative estimation of the relationship between the structure and reactivity of molecules in free-radical processes called reactivity of molecules in free-radical processes called r r 7 72 2 -analysis -analysis is proposed. The bibliography includes 238 references. is proposed. The bibliography includes 238 references.

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Section: Critical Analysis Of the Existing Approachesmentioning

confidence: 99%

Correlation analysis in the chemistry of free radicals

Cherkasov¹,

Jönsson²,

Галкин³

et al. 2001

Russ. Chem. Rev.

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ChemInform Abstract: USE OF TWO‐PARAMETER CORRELATIONS FOR STUDYING THE RADICAL REACTIVITY OF AROMATIC COMPOUNDS

Afanas’ev¹

1981

Chemischer Informationsdienst

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Nucleophilic character of the tert‐butyl radical. Absolute rate constants for the reactions with substituted toluenes

Dütsch

Fischer

1982

Int J of Chemical Kinetics

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The decay of photochemically generated tert-butyl radicals is studied at 48°C in 11 n-and p -substituted toluenes by time-resolved electron spin resonance spectroscopy. It is governed by the second-order self-termination perturbed by a pseudo-first-order reaction of the radical with the toluenes. The first-order lifetimes yield the rate constants k A for hydrogen transfer from toluenes to tert-butyl. Substituent effects on the rate constants confirm the nucleophilic character of the radical.Rate constants for the abstraction of a benzylic hydrogen atom from mand p-substituted toluenes by many neutral radicals are known to obey, at least approximately, the Hammett p a relation [l] (1) h i is the rate constant for unsubstituted toluene, and a is a substituent parameter. This correlation is often interpreted in terms of polar resonance structures contributing to the transition state and lowering the activation energy. The sign of the reaction parameter p classifies radicals as electro-( p < 0) or nucleophilic ( p > 0). For most radicals a negative p is found [I].It has been argued [2] that for this case the correlation can also be explained in terms of substituent effects on the dissociation energy of the benzylic CH bond without resorting to polar transition states. The few published examples for radicals with positive p values [3-71 are of deciding importance, therefore. Usually correlation (1) is based not on absolute rate constants but on relative rate constants derived from relative product yields in reaction systems where the hydrogen abstraction reaction from the toluene competes with the reaction of the radical with a suitable added standard. Using deuterated thiols as standards, Pryor et al. [3,4] obtained the hitherto highest positive p reported, p = 1.0, for the tert-butyl radical at log(KA/K;) = p -a

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Use of two‐parameter correlations for studying the radical reactivity of aromatic compounds

Cited by 7 publications

References 57 publications

Correlation analysis in the chemistry of free radicals

Correlation analysis in the chemistry of free radicals

ChemInform Abstract: USE OF TWO‐PARAMETER CORRELATIONS FOR STUDYING THE RADICAL REACTIVITY OF AROMATIC COMPOUNDS

Nucleophilic character of the tert‐butyl radical. Absolute rate constants for the reactions with substituted toluenes

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