A Quantitative Treatment of Isomer Distribution in Aromatic Electrophilic Substitution<sup>1,2</sup>

McGary, C. W.; Okamoto, Y.; Brown, Herbert C.

doi:10.1021/ja01616a035

Cited by 28 publications

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“…The E 5 values of compounds 1, 3, 6, 8, 10, 12, 14, 15, 20, 23-25, 27, and 30 were converted from the potential values at pH 7 (E 7 ) or other pH (Steenken & Neta, 1982;Lind et al, 1990;Jovanovic et al, 1991) as described by Jovanovic et al (1991). The E 5 values of compounds 2, 4, 5, 7, 9, 12, 11, 21, and 22 were converted from E 7 values which were estimated by the correlation of E 7 ) 0.95 + 0.31σ + (Jovanovic et al, 1991) and the published σ + values (McGary et al, 1955) for the substituents involved. An E 5 (32) of 0.9 V was estimated from E 5 (8) ) 2 ) of 0.58 V and E 5 (4-NH 2 -C 6 H 5 OH) of 0.53 V were converted from the values of Steenken and Heta (1982).…”

Section: T H I S C O N T E N T Imentioning

confidence: 99%

Oxidation of Phenols, Anilines, and Benzenethiols by Fungal Laccases: Correlation between Activity and Redox Potentials as Well as Halide Inhibition

1996

Biochemistry

655

430

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A comparative study has been performed with several fungal laccases for the oxidation of a series of phenols, anilines, and benzenethiols and for the inhibition by halides. The observed K(m) and kcat were correlated to the structure of substrate. The change in log (kcat/K(m)) was found to be proportional to the one-electron redox potential difference between laccase's type 1 copper site and substrate. This correlation indicated that the first electron transfer from substrate to laccase was governed by the "outersphere" mechanism. Compared to the electronic factor, the steric effect of small o-substituents (such as methyl and methoxy groups) was found to be unimportant. The depth of the laccase's type 1 copper site was estimated as approximately 10 A by comparing the steric effect among five 2-methoxyphenols whose 4-substituents ranged from 0.1 to 14 kDa in mass. The observed inhibition potency order of F- > Cl- > Br- was attributed to limited accessibility of laccase's type 2/type 3 trinuclear copper cluster site. Although the enzymes studied have homologous primary sequences and predicted similar backbone structures, the difference exhibited by each enzyme (in interacting with individual substrate or inhibitor) suggested the structural variation in their functional domains.

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Section: T H I S C O N T E N T Imentioning

confidence: 99%

Oxidation of Phenols, Anilines, and Benzenethiols by Fungal Laccases: Correlation between Activity and Redox Potentials as Well as Halide Inhibition

1996

Biochemistry

655

430

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“…The use of the Hammett a and the Brown v+ substituent constants in the investigation of structure-reactivity relationships is well established (1). In their studies on electrophilic aromatic substitution, Brown and coworkers (2) recognized that the original Hammett o constants, derived from the ionization of substituted benzoic acids, required modification to allow for the different electron demand situations at the reaction site. Thus Brown and Okamoto (3) estimated the electrophilic substituent constants v+ from the solvolysis of substituted tert-cumyl chlorides in aqueous acetone.…”

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confidence: 99%

Structural effects in solvolytic reactions; carbon-13 NMR studies of carbocations ^† : Effect of increasing electron demand on the carbon-13 NMR shifts in substituted tert -cumyl and 1-aryl-1-cyclopentyl carbocations—correlation of the data by a new set of substituent constants, σ ^C+

Brown

Kelly

Periasamy

1980

Proc. Natl. Acad. Sci. U.S.A.

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The cationic carbon substituent chemical shifts (,AC+) for nine representative meta-substituted tert-cumyl carbocations are correlated satisfactorily by the r+ substituent constants (slope p+ = -18.18, correlation coefficient r = 0.990).However, the substituent chemical shifts (A5C+) for the corresponding para derivatives are not correlated by the a+ substituent constants. The possibility of developing a set of suiistituent constants capable of correlating such I'C NMR shifts was examined. The slope of the line defined by the meta substituents (p+ = -18.18) was utilized to calculate &+ constants for both meta and para substituents. The utility of these constants was then tested by their ability to correlate the 13C NMR shifts in the cations for a different system, the 1-aryl-1-cyclopentyl cations. Indeed, these &+ values correlate very well with the AC+ values, yielding pc+ = -16.84, r = 0.999. The use of the Hammett a and the Brown v+ substituent constants in the investigation of structure-reactivity relationships is well established (1). In their studies on electrophilic aromatic substitution, Brown and coworkers (2) recognized that the original Hammett o constants, derived from the ionization of substituted benzoic acids, required modification to allow for the different electron demand situations at the reaction site. Thus Brown and Okamoto (3) estimated the electrophilic substituent constants v+ from the solvolysis of substituted tert-cumyl chlorides in aqueous acetone. These constants provide a measure of the stabilizing effect of the substituent on the reaction center of the transition state.These constants have been systematically applied in studies of structural effects in solvolytic reactions (4). On the basis of the usual assumption of a late transition state in such solvolytic processes (5), it was not unreasonable to anticipate that these substituent constants could also be used to correlate the stabilities of the carbocationic intermediates produced in such solvolyses. Indeed, a large body of consistent information has been accumulated as to the effect of substituents on the stabilities of such carbocations (4).In recent years it has become possible to prepare and observe such carbocations in super acid media (6). The '3C NMR chemical shift in such carbocations has been taken as a measure of the electron delocalization and stabilization of the cations (6). Accordingly, attempts have been made to correlate the 13C NMR shifts with the a+ values (7-9).For example, Olah and coworkers reported approximate linearity in the plot of 13C NMR shifts (3C+) of the cationic carbon of substituted tert-cumyl cations against a+ constants (7,8 only a fair fit, with the correlation coefficient being r = 0.976, considerably poorer than the fits realized in correlations involving solvolytic processes (4).In a reinvestigation of the behavior of the substituted tertcumyl cations, Kelly and Spear (10) realized an even lower correlation coefficient, r = 0.967. Even more important, they pointed out that the least-s...

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“…We now turn to a more quantitative analysis of the bromination kinetics. In the past, several research groups studied the bromination of styrene (or styrene-like monomers) as well as polystyrene under various conditions. − ,− ,− For instance, Robertson et al reported that the bromination of mesitylene in acetic acid follows a second-order kinetics at low bromine concentrations (10 −2 −10 −3 M). − Andrews , and Wright groups argued that bromination substitution follows a combined first-order (in bromine) and second-order (in bromine) reaction kinetics. R = − d [ Br 2 ] d t = k 1 [ ArH ] [ Br 2 ] + k 2 [ ArH ] [ Br 2 ] 2 …”

Section: Resultsmentioning

confidence: 99%

“…In the past, several research groups studied the bromination of styrene (or styrene-like monomers) as well as polystyrene under various conditions. [27][28][29][30][32][33][34][66][67][68][69][70][71][72] For instance, Robertson et al reported that the bromination of mesitylene in acetic acid follows a second-order kinetics at low bromine concentrations (10 -2 -10 -3 M). [73][74][75] Andrews 76,77 and Wright groups 31 argued that bromination substitution follows a From their data it appears that the second-order kinetics in bromine is most dominant because k 1 /k 2 , 1.…”

Section: Resultsmentioning

confidence: 99%

Effect of Solvent Quality and Chain Confinement on the Kinetics of Polystyrene Bromination

2008

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We report on the kinetics of the bromination of free polystyrene (PS) chains in bulk solution and those anchored on flat solid substrates by performing the bromination reaction in different solvents, including nitrobenzene (NB), 1-chlorodecane (CD), 1-chloroundecane (CUD), and 1-chlorododecane (CDD), at various temperatures. We find that bulk bromination of PS follows the second-order kinetic in bromine and the reaction rate increases with increasing dielectric constant of the solvent (ε). In spite of ε CDD > ε CD , the bulk bromination kinetics of PS in CDD is slower than that in CD because of lower solubility of PS in CDD than in CD. In addition, we demonstrate that the reaction rates for brominating PS brushes anchored to flat solid substrates are much slower than those for brominating free PS chains in bulk solution. We attribute this behavior to steric hindrance due to PS confinement on the substrate.

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A Quantitative Treatment of Isomer Distribution in Aromatic Electrophilic Substitution^1,2

Cited by 28 publications

References 0 publications

Oxidation of Phenols, Anilines, and Benzenethiols by Fungal Laccases: Correlation between Activity and Redox Potentials as Well as Halide Inhibition

Oxidation of Phenols, Anilines, and Benzenethiols by Fungal Laccases: Correlation between Activity and Redox Potentials as Well as Halide Inhibition

Structural effects in solvolytic reactions; carbon-13 NMR studies of carbocations ^† : Effect of increasing electron demand on the carbon-13 NMR shifts in substituted tert -cumyl and 1-aryl-1-cyclopentyl carbocations—correlation of the data by a new set of substituent constants, σ ^C+

Effect of Solvent Quality and Chain Confinement on the Kinetics of Polystyrene Bromination

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A Quantitative Treatment of Isomer Distribution in Aromatic Electrophilic Substitution1,2

Cited by 28 publications

References 0 publications

Oxidation of Phenols, Anilines, and Benzenethiols by Fungal Laccases: Correlation between Activity and Redox Potentials as Well as Halide Inhibition

Oxidation of Phenols, Anilines, and Benzenethiols by Fungal Laccases: Correlation between Activity and Redox Potentials as Well as Halide Inhibition

Structural effects in solvolytic reactions; carbon-13 NMR studies of carbocations † : Effect of increasing electron demand on the carbon-13 NMR shifts in substituted tert -cumyl and 1-aryl-1-cyclopentyl carbocations—correlation of the data by a new set of substituent constants, σ C+

Effect of Solvent Quality and Chain Confinement on the Kinetics of Polystyrene Bromination

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A Quantitative Treatment of Isomer Distribution in Aromatic Electrophilic Substitution^1,2

Structural effects in solvolytic reactions; carbon-13 NMR studies of carbocations ^† : Effect of increasing electron demand on the carbon-13 NMR shifts in substituted tert -cumyl and 1-aryl-1-cyclopentyl carbocations—correlation of the data by a new set of substituent constants, σ ^C+