Kinetic isotope effects chloride

Solvolytic experiments specifically designed to test Bartell s theory were carried out by Karabatsos et al. (1967), who were primarily interested in an assessment of the relative contributions of hyperconjugation and non-bonded interactions to secondary kinetic isotope effects. Model calculations of the (steric) isotope effect in the reaction 2- 3 were performed, as well as that in the solvolyses of acetyl chloride... 

Interest has been shown by several groups on the effect of solvent and of added anions upon the oxidation of alcohols. The oxidation of isopropanol proceeds 2500 times faster in 86.5 % acetic acid than in water at the same hydrogen ion concentration . The kinetics and primary kinetic isotope effect are essentially the same as in water. Addition of chloride ion strongly inhibits the oxidation and the spectrum of chromic acid is modified. The effect of chloride ion was rationalised in terms of the equilibrium,... 

More recent theoretical work has raised questions about these conclusions, how-ever. Particularly extensive calculational treatment of the rearrangement of 54 to vinyl chloride by several research groups failed to duplicate the predictions of an atypical kinetic isotope effect. These later studies indicate that tunneling effects should indeed be greater for H-shift than for the heavier D rearrangement. Consequently, the k /ko ratio should actually decrease at higher temperatures. The discrepancy in predicted results was eventually traced to an error in the earlier calculations. Nevertheless, it... 

The most recent addition to Shine s extensive study of the benzidine-type rearrangements41 involved remeasuring the nitrogen and the carbon-13 and carbon-14 kinetic isotope effects at the 4- and at the 4- and 4 -carbons as well as determining the carbon-13 and carbon-14 isotope effects at the 1- and at the 1- and l -carbons in the benzidine rearrangement of hydrazobenzene (equation 30). The reaction, which was carried out in 75% aqueous ethanol that was 0.1 M in hydrochloric acid and 0.3 M in lithium chloride at 0°C, gave an 86% yield of benzidine (11) and a 14% yield of diphenyline (12). The kinetic isotope effects found for the formation of benzidine and diphenyline under these reaction conditions are presented in Table 5. 

TABLE 5. The nitrogen, carbon-13 and carbon-14 kinetic isotope effects found for the acid-catalyzed benzidine rearrangement of hydrazobenzene in 75% aqueous ethanol that was 0.1 M in hydrochloric acid and 0.3 M in lithium chloride at 0°C... 

Secondary hydrogen kinetic isotope effects are further classified as alpha, beta, etc. depending on the distance of the isotopically substituted atom from the bond(s) that is (are) being made or broken (a = 1 bond, 3 = 2 bonds, etc.). Consider the simple Sn2 reaction between hypochlorite anion and ethyl chloride ... 

The haloalkane dehalogenase DhlA mechanism takes place in two consecutive Sn2 steps. In the first, the carboxylate moiety of the aspartate Aspl24, acting as a nucleophile on the carbon atom of DCE, displaces chloride anion which leads to formation of the enzyme-substrate intermediate (Equation 11.86). That intermediate is hydrolyzed by water in the subsequent step. The experimentally determined chlorine kinetic isotope effect for 1-chlorobutane, the slow substrate, is k(35Cl)/k(37Cl) = 1.0066 0.0004 and should correspond to the intrinsic isotope effect for the dehalogenation step. While the reported experimental value for DCE hydrolysis is smaller, it becomes practically the same when corrected for the intramolecular chlorine kinetic isotope effect (a consequence of the two identical chlorine labels in DCE). 

We have examined the proton transfer reaction AH-B A -H+B in liquid methyl chloride, where the AH-B complex corresponds to phenol-amine. The intermolecular and the complex-solvent potentials have a Lennard-Jones and a Coulomb component as described in detail in the original papers. There have been other quantum studies of this system. Azzouz and Borgis performed two calculations one based on centroid theory and another on the Landau-Zener theory. The two methods gave similar results. Hammes-Schiffer and Tully used a mixed quantum-classical method and predicted a rate that is one order of magnitude larger and a kinetic isotope effect that is one order of magnitude smaller than the Azzouz-Borgis results. 

A missing kinetic isotope effect, as well as adsorption studies in the presence of strongly adsorbing anions, such as chloride, are in favor of Yeager s mechanistic proposition [78]. 

Typical acidic catalysts are silica—alumina, transition metal sulphates or chlorides, calcium phosphate etc. They are characterised by low deuterium kinetic isotope effects and low stereoselectivity (see Tables 8,11 and 12). These results correspond to the E2cA or El mechanisms, between which a transition may be observed due to the influence of the structure of the reactants, i.e. according to the polarity of the Ca—X and Cp—H bonds. Again, the reactions of 1,2-dibromoethane and 1,1,2,2-tetrachloroethane yielded the evidence. The deuterium kinetic isotope effect on silica—alumina was 1.0 for the dibromo-derivative, which indicates a pure El mechanism, whereas for the tetrachloro-derivative, the value of 1.5 was found. 

In the early papers (26, 17) on homogeneous hydrogenation by tris(triphenylphosphine)rhodium(I) chloride, Wilkinson and coworkers found the kinetic isotope effect for deuterium addition to be... 

Finally, a study in which six different kinetic isotope effects for the. S n2 reaction between cyanide ion and ethyl chloride were measured in DMSO and in THF has shown that the transition state in THF was only slightly tighter than that in DMSO with very slightly shorter NC-C and Ca-Cl bonds,61 and another on the effect of the solvent, leaving group, and source of the fluoride ion in synthesizing organic fluorides is discussed above.65... 

The competition between nucleophilic substitution and base-induced elimination in the gas phase has been studied using deuterium kinetic isotope effects (KIE).6 The overall reaction rate constants and KIE have been measured for the reactions of RC1 + CIO- (R = Me, Et, t -Pr, and r-Bu). As the extent of substitution in the alkyl chloride increases, the KIE effects become increasingly more normal. These results indicated that the E2 pathway becomes the dominant channel as the alkyl group becomes more sterically hindered. 

Mechanisms have been suggested for the N-bromosuccinimide (NBS) oxidation of cyclopentanol and cyclohexanol, catalysed by iridium(III) chloride,120 of ethanolamine, diethanolamine, and triethanolamine in alkaline medium,121 and for ruthenium(III)-catalysed and uncatalysed oxidation of ethylamine and benzylamine.122 A suitable mechanism has been suggested to explain the break in the Hammett plot observed in the oxidation of substituted acetophenone oximes by NBS in acidic solution.123 Oxidation of substituted benhydrols with NBS showed a C-H/C-D primary kinetic isotope effect and a linear correlation with er+ values with p = —0.69. A cyclic transition state in the absence of mineral acid and a non-cyclic transition state in the presence of the acid are proposed.124 Sulfides are selectively oxidized to sulfoxides with NBS, catalysed by ft-cyclodextrin, in water. This reaction proceeds without over-oxidation to sulfones under mild conditions.125... 

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