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Heterolysis of t-BuBr and t-BuI in aprotic solvents involves a DH 3DS compensation effect.The DG of t-BuBr heterolysis in aprotic solvents decreases with increasing solvent polarity and cohesion, whereas the respective value for t-BuI heterolysis decreases with increasing solvent polarity, nucleophilicity, and polarizability. In protic solvents, a negative effect of nucleophilic solvation is observed.The correlation analysis of the effects of solvent parameters (ionizing ability, polarity, polarizability, electrophilicity, nucleophilicity, cohesion) on the rates of monomolecular heterolysis reactions (SN1, E1, solvolysis) in terms of many-parameter linear free energy equations has given insight into the nature of solvation effects [237]. Most commonly, solvent effects on log rate constants or, what is the same, activation Gibbs energies are studied. However, these values are strongly temperature-dependent [438]. The activation Gibbs energy is determined by the activation enthalpy and entropy (DG = DH 3 TDS ), which are almost invariable in the experimental temperature range. Studying solvent effects on these activation parameters makes it possible to understand the nature of solvation effects and to reveal the mechanism of transition state solvation [9313]. However, such studies have been few in number.

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“…(10)]. The contribution of this parameter in the less nucleophilic medium is consistent with the assumption of its artifactual origin.…”

supporting

confidence: 81%

Kinetics and mechanism of monomolecular heterolysis of commercial organohalogen compounds: XXXVIII. Correlation analysis of solvent effects on the activation parameters of heterolysis of t-BuBr and t-BuI

2004

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“…Figure shows the ΔH ≠ -ΔS ≠ and ΔG ≠ -ΔS ≠ plots for the heterolysis of 1-chloro-1-methylcyclohexane (VI) [42], 7α-bromocholesteryl benzoate (VII) [43], 1-bromo-1-methylcyclohexane (VIII) [44], 1-bromo-1-methylcyclopentane (IX) [44], and p-methoxybenzotrichloride (X) [45] in cyclohexane. The rates of heterolysis of these substrates are fairly similar, ΔG ≠ = 128 ± 2 kJ/mol, ΔH ≠ changes from 157 to 59 kJ/mol, and ΔS ≠ changes from 92 to -234 J × mol -1 K -1 .…”

Section: Substratementioning

confidence: 99%

“…This means that in the first case the observed variations are determined by ∆S ≠ , and in the second, by ∆H ≠ . As a rule, aprotic solvents solvate bromides to a stronger extent as compared to chlorides [44]. Presumably, acetonitrile provides additional solvation of chlorosubstituted derivatives due to formation of linear quadrupole R δ+ -Cl δ-· · · H δ+ -δ-CH 2 CN.…”

Section: XImentioning

confidence: 99%

Kinetics and mechanism of unimolecular heterolysis of cage-like compounds: XXI. Solvent effect on the realtive rate of heterolysis of 2-methyland 2-phenyl-2-haloadamantanes. Role of activation parameters

et al. 2009

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The kinetics of heterolysis of 2-chloro-2-methyladamantane, 2-bromo-2-methyladamantane, 2-chloro-2-phenyladamantane, and 2-bromo-2-phenyladamantane in isopropyl alcohol, tert-butyl alcohol, acetonitrile, nitromethane, cyclohexanone, and γ-butyrolactone were studied using the verdazyl technique. The rate constant ratio k Ph /k Me decreases from three orders of magnitude to unity in the solvent series BuOH > i-PrOH > t-BuOH > MeCN > PhNO 2 > cyclohexanone > γ-butyrolactone > sulfolane, which results from weakening of conjugation between the phenyl group and emerging carbocationic center. The effect of solvent on the entropy and enthalpy of heterolysis in going from 2-methyl-substituted 2-haloadamantanes to their 2-phenyl analogs is discussed. * For communication XX, see [1].

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“…For example, the activation free energy of heterolysis of 1-methyl-1-chlorocyclopentane in eight solvents (nos. 339, 11) grows with an increase in the solvent nucleophilicity and polarizability [22]: A decrease in the reaction rate with an increase in the solvent polarizability is associated with the negative effect of the nucleophilic solvation, since an increase in the solvent polarizability favors the nucleophilic solvation of the contact ion pair.…”

Section: äääääääääääämentioning

confidence: 99%

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XLII. Effect of Aprotic Solvent on the Rate of 3-Methyl-3-chloro-1-butene Dehydrochlorination. Correlation Analysis of Solvation Effects

2005

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The kinetics of 3-methyl-3-chloro-1-butene dehydrochlorination in propylene carbonate, g-butyrolactone, sulfolane, acetone, MeCN, PhNO 2 , PhCN, PhCOMe, MeCOEt, cyclohexanone, o-dichlorobenzene, PhCl, PhBr, 1,2-dichloroethane, dioxane, and AcOEt were studied; v = k[C 5 H 9 Cl], E1 mechanism. The reaction rate is satisfactorily described by the parameters of the polarity, electrophilicity, and cohesion of the solvent; the solvent nucleophilicity and polarizability exert no effect on the reaction rate.

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Cited by 6 publications

References 12 publications

Kinetics and mechanism of monomolecular heterolysis of commercial organohalogen compounds: XXXVIII. Correlation analysis of solvent effects on the activation parameters of heterolysis of t-BuBr and t-BuI

Kinetics and mechanism of monomolecular heterolysis of commercial organohalogen compounds: XXXVIII. Correlation analysis of solvent effects on the activation parameters of heterolysis of t-BuBr and t-BuI

Kinetics and mechanism of unimolecular heterolysis of cage-like compounds: XXI. Solvent effect on the realtive rate of heterolysis of 2-methyland 2-phenyl-2-haloadamantanes. Role of activation parameters

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XLII. Effect of Aprotic Solvent on the Rate of 3-Methyl-3-chloro-1-butene Dehydrochlorination. Correlation Analysis of Solvation Effects

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