Photobrominations of Substituted Cumenes by <i>N</i>-Bromosuccinimide:  Charge Delocalizations, Inductive Effects, and Spin Dispersions Triggered by Substituents

Kim, Sung Soo; Kim, Chun Soo

doi:10.1021/jo9905468

Cited by 10 publications

(7 citation statements)

References 25 publications

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“…Such modest substituent effects engender differential free energies of activation ΔΔ of less than 1 kcal mol -1 . On the other hand, a larger magnitude of the same entity ( ΔΔ > 1 kcal mol -1 ) was observed for the radical reactions involving polar TS . The modest alterations of the rates suggest that substituent effects may be mainly derived from other than polar interactions via delocalizations of positive charge .…”

Section: Resultsmentioning

confidence: 85%

“…The concept of Hammett substituent constants for radical reactions (σ • ) was introduced for the first time by Streitwieser and Perrin as an index of spin-delocalizations. However, the polar effects − caused by substituents have been found to outweigh the spin-delocalization effects in determining the rates of numerous radical reactions. Furthermore, separation of the latter from the former engenders extreme difficulty.…”

Section: Introductionmentioning

confidence: 99%

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Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Kim

Zhu

2000

J. Org. Chem.

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Rate constants (k(Y)) of the isomerizations of 11 diphenyl N-(substituted benzyl) ketenimines were measured at 40, 50, 60, and 70 degrees C. Activation parameters DeltaH()(Y) and DeltaS()(Y) were obtained using the Eyring equation. The relative rates (k(Y)/k(H)) were fitted into Hammett single correlations (log k(Y)/k(H) = rhosigma and log k(Y)/k(H) = rho(*)sigma(*)). The single correlations have been compared with Hammett dual correlations (log k(Y)/k(H) = rhosigma + rho(*)sigma(*) ). Separate treatments of para and meta substituents yielded even better correlations. Para substituents control the rates through spin-delocalizations and inductive effects. The former outweighs the latter when the latter exerts a modest but distinct influence on the rates. On the other hand, inductive effects are the "major" or the sole interactions triggered by meta substituents.

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Section: Resultsmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Kim

Zhu

2000

J. Org. Chem.

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“…e . , ΔΔ H ⧧ Y - H ≈ 0) for β-scissions of the carbinyloxy radicals 10 and photobrominations of substituted cumenes . This phenomenon 10,11 has been rationalized in terms of the cancellation of the opposite effects invoked by a and b .…”

Section: Resultsmentioning

confidence: 94%

“…The steeper slope (α 2 = −5.22) may again suggest that the substituents influence the rates through entropic variations. The relative rates of the five substituents either slightly increase or stay constant with higher temperatures (a sign arguing for entropy control of rates). − Such pattern of relative rates violates reactivity/selectivity principle (RSP) and can be rationalized with eq 7. Drastic skeletal alterations of R in RCO 3 C(CH 3 ) 3 may engender rates of the thermolysis to be influenced by an enthalpy factor.…”

Section: Resultsmentioning

confidence: 99%

“…Hydrogen atom abstractions from substituted toluenes and cumenes and β - scissions of the carbinyloxy radicals 10 reveal entropy control of rates via the polar substituent interactions. Only relative rates were available with previous studies 9-11 thereby providing differential activation terms (ΔΔ H ⧧ Y - H and ΔΔ S ⧧ Y - H ) derived from the Eyring equation .…”

Section: Introductionmentioning

confidence: 99%

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Thermolysis of tert-Butyl Phenylperacetates: Delicate Control of the Rates through Contributions from Translational and Rotational Entropy

et al. 2001

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The first-order rate constants (k(Y)) at several temperatures in CDCl(3) were measured for thermal decompositions of YC(6)H(4)CH(2)CO(3)C(CH(3))(3) with Y being p-OCH(3), p-OPh, p-CH(3), p-Ph, p-H, p-Cl, m-Cl, and p-NO(2). The relative rates (k(Y)/k(H)) exhibit excellent rho(+)/sigma(+) Hammett correlations with rho(+) < 0, indicating a polar TS. Activation parameters (DeltaH()(Y) and DeltaS()(Y)) and their differential terms (DeltaDeltaH()(Y)(-)(H) and DeltaDeltaS()(Y)(-)(H)) were obtained from the Eyring plot. Differential activation terms (DeltaDeltaH()(Y)(-)(H) and DeltaDeltaS()(Y)(-)(H)) disclose an isokinetic relation with p-CH(3), p-Ph, p-H, p-Cl, and m-Cl (isokinetic temp, 230 K). However, p-OCH(3), and p-OPh show negative deviations, and a positive deviation occurs with p-NO(2). Plot of DeltaDeltaH()(Y)(-)(H) vs sigma(+) exhibits a good linear relation (r = 0.95) with a slope (alpha(1) = -3.34). A better linear correlation (r = 0.97) and steeper slope (alpha(2) = -5.22) were observed for TDeltaDeltaS()(Y)(-)(H) vs sigma(+). Negatively larger slope (alpha(2) = -5.22) may point to entropy control of rates. Differential activation parameters (DeltaDeltaH()(Y)(-)(H) and DeltaDeltaS()(Y)(-)(H)) reflect variations of activation process. Differential activation entropies (DeltaDeltaS()(Y)(-)(H)) are discussed in terms of contributions of translational and rotational entropies. Similar deviation behaviors of p-OCH(3), p-OPh, and p-NO(2) were again observed for the both plots. p-NO(2) can strongly destabilize the cationic site of the polar TS but serves an eminent spin delocalizer for the homolytic TS.

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Polar Effects in Decomposition of Peroxidic Compounds and Related Reactions

Kim

2009

Patai's Chemistry of Functional Groups

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Photobrominations of Substituted Cumenes by N-Bromosuccinimide: Charge Delocalizations, Inductive Effects, and Spin Dispersions Triggered by Substituents

Cited by 10 publications

References 25 publications

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Thermolysis of tert-Butyl Phenylperacetates: Delicate Control of the Rates through Contributions from Translational and Rotational Entropy

Polar Effects in Decomposition of Peroxidic Compounds and Related Reactions

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Photobrominations of Substituted Cumenes by N-Bromosuccinimide: Charge Delocalizations, Inductive Effects, and Spin Dispersions Triggered by Substituents

Cited by 10 publications

References 25 publications

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ•) Constants for Spin-Delocalizations

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ•) Constants for Spin-Delocalizations

Thermolysis of tert-Butyl Phenylperacetates: Delicate Control of the Rates through Contributions from Translational and Rotational Entropy

Polar Effects in Decomposition of Peroxidic Compounds and Related Reactions

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Product

Resources

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Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations