Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXVIII. Effect of the Nature of the Verdazyl Indicator on Salt Effects in Dehydrobromination of 3-Bromocyclohexene in Nitrobenzene

The salt effect on the rate of dehydrobromination of 3-bromocyclohexene in PhNO2 depends on the nature of the verdazyl indicator. With triphenylverdazyl and its chloro and nitro derivatives in the presence of Et₄NClO₄, a normal salt effect is observed, in the presence of bromides, a superposition of normal and special salt effects, while in the presence of chlorides, a superposition of normal and special negative salt effects. With the dimethoxy verdazyl derivative, a normal salt effect is always observed.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXIX. Salt Effect of LiClO<Subscript>4</Subscript>in Heterolysis of Ph<Subscript>2</Subscript>CHCl in γ-Butyrolactone

Additions of LiClO₄ accelerate the heterolysis of Ph₂CHCl in γ-butyrolactone; v = k[Ph₂CHCl], SN1 mechanism. The salt effect increases with an increase in the electron-acceptor properties of the verdazyl indicator. A superposition of three salt effects (normal, special, and negative special) is observed.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 1, 2005, pp. 105–110.Original Russian Text Copyright © 2005 by Dvorko, Ponomareva, Golovko, Pervishko.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXVII.1 Effect of Nucleofuge and Solvent of the Relative Rates of Heterolysis of 1-Halo-1-methylcyclopentanes and 1-Halo-1-methylcyclohexanes. Correlation Analysis of Solvation Effects

The effect of solvent ionizing ability on heterolysis rate enhances in the series 1-chloro-1-methylcyclohexane < 1-bromo-1-methylcyclohexane 1-chloro-1-methylcyclopentane < 1-bromo-1-methyl- cyclopentane. The lower sensitivity of cyclohexyl substrates compared with cyclopentyl is determined by conformational effects. Bromides are more sensitive to solvent effects than chlorides because of the stronger polarizability of the C-Br bond.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXIII.1 Correlation Analysis of Solvation Effects in Monomolecular Heterolysis of 1-Bromo-1-methylcyclopentane, 1-Bromo-1-methylcyclohexane, and 2-Bromo-2-methyladamantane

The rate of heterolysis of 1-bromo-1-methylcyclopentane and 1-bromo-1-methylcyclohexane is determined by the equation v = k[RBr], mechanism E1. Comparative correlation analysis of solvation effects in heterolysis of these substrates and 2-brom-2-methyladamantane was performed.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXV.1 Solvation Effects on the Activation Parameters of Heterolysis of 1-Bromo-1-methylcyclopentane and 1-Bromo-1-methylcyclohexane. Correlation Analysis of Solvation Effects

Kinetics of heterolysis of 1-bromo-1-methylcyclopentane and -cyclohexane in protic and aprotic solvents were studied. Correlation analysis of the effect of solvent parameters on G , H , and S was performed.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXVI.1 Solvent Effect on the Activation Parameters of Heterolysis of 1-Methyl-1-chlorocyclohexane. Correlation Analysis of Solvation Effects in Heterolysis of 1-Methyl-1-chlorocyclohexane and 1-Methyl-1-chlorocyclopentane

The kinetics of heterolysis of 1-methyl-1-chlorocyclohexane in six protic and eight aprotic solvents at 25-50°C was studied by the verdazyl method; v = k[RCl], E1 mechanism. The correlation analysis of the solvent effects on the activation free energy G , enthalpy H , and entropy S of heterolysis of 1-methyl-1-chlorocyclohexane and 1-methyl-1-chlorocyclopentane was performed for the same sets of solvents.     

Triphenylphosphine as an effective catalyst for ketoximes addition to acylacetylenes: regio- and stereospecific synthesis of (E)-(O)-2-(acyl)vinylketoximes

Triphenylphosphine catalyzes the regio- and stereospecific addition of ketoximes to acylacetylenes, whereas classical conditions using acetylene (KOH/DMSO, 70 °C) are unsuitable for this purpose. The reaction proceeds under mild conditions (CH₂Cl₂, rt, 7 h) to afford (E)-(O)-2-(acyl)vinylketoximes (92-98% stereoselectivity) in a yield of up to 85%. The (E)-adducts obtained are energetically less favorable than the corresponding (Z)-isomers and are gradually enriched with (Z)-isomers, thus indicating the kinetic control of (E)-stereoselectivity of the reaction.     

Electron transfer to a carbon triple bond

On mixing of solutions of KCNS or KI with the methyl esters of acetylenedicarboxylic and propiolic acid or acetic-propiolic anhydride in dimethylformamide, an EPR signal arises, the intensity of which increases rapidly with time. The rate of formation of paramagnetic substances increases with the electrophilicity of the carbon triple bond and with the nucleophilicity of the salt anion. The emergence of an EPR signal is due to the complete transfer of an electron from the salt anion to the triple bond of the unsaturated compound with formation of -C=- anion radicals. Oxygen and proton donors are inhibitors of this reaction.     

Nature of solvation effects and mechanism of heterolysis of <Emphasis Type="Italic">tert</Emphasis>-alkyl halides

Specificities of heterolysis of tert-alkyl halides in protic and aprotic solvents were analyzed. Values of log k ₂₅ for heterolysis of tert-butyl chloride, tert-butyl bromide, tert-butyl iodiede, 1-chloro-1-methylcyclopentane, 1-chloro-1-methylcyclohexane, 1-bromo-1-methylcyclopentane, 1-bromo-1-methylcyclohexane, 2-chloro-2-phenylpropane, 1-iodoadamantane, and 2-bromo-2-methyladamantane in 19 to 44 solvents, determined mostly by the verdazyl technique were collected. Correlation analysis of solvation effects was performed in terms of multiparameter equations based on the linear free energy relationship principle, as well as in the logk-E _T coordinates. The nature of solvation effects and mechanism of heterolysis of a covalent C-Hlg bond were discussed.