Solvolysis activation parameters

In inert systems such as technetium and rhenium, ligand substitution reactions-including solvolysis-proceed under virtually irreversible conditions. Thus, the nature of the reaction center, the nature of the leaving group, and the nature and position of the other ligands in the complex affect the rates and activation parameters in a complicated manner. Most substitution reactions take place via interchange mechanisms. This is not too surprising when the solvent is water - or water-like - and where, in order to compete with the solvent,... 

Kinetics of the solvolysis of acyl chlorides and alkyl chlorides in hydroxylic solvent mixtures have been measured conductimetrically at various temperatures and pressures. The activation parameters A V, AH, and AS were calculated from the rate constants. The authors appear to have been interested mainly in acyl chlorides, but conclude that, whereas p-methylbenzoyl chloride reacts via a dissociative... 

Alkyl, halo, and the other substituents exhibiting a modest influence on the rate of solvolysis of the tertiary chloride were examined under the standard conditions selected as 90% aqueous acetone at 25° (Brown et al., 1957a Brown et al., 1957b). The extension of the study to highly activating and deactivating substituents required the use of special procedures for the estimation of rate data under the standard conditions. It was convenient in most instances to determine the activation parameters at suitable temperatures and calculate the rate at 25°. For more extreme variations in reactivity, as with p-methoxy- and p-nitro-phenyldimethylcarbinyl chloride, both the temperature and composition of the solvent were modified (Okamoto and Brown, 1957b). These... 

Rate Constants, Relative Rates, and Activation Parameters for the Solvolysis of Monosubstituted Phenyldimethylcarbinyl Chlorides in 90% Aqueous Acetone... 

Perhaps the most spectacular success of explanations based on solvation of ground states, published to date, is the dissection of activation parameters for solvolysis of t-butyl chloride in mixtures of ethanol and water, first discussed by Winstein and Fainberg (1957). The complex variation of AH and AS (Fig. 21) has been shown to be due almost entirely to ground state solvation effects, at least for the solvents ethanol—40% ethanol/water studied by Arnett et al. (1965). For 90%, 80%, 70%, 60%, 50% and 40% ethanol/water the parameter AH1 for solvation of the transition state (by transfer from the gas phase) was calculated to be linearly proportional to the corresponding value of AS, as expected from the behaviour of simple salts. The point for pure ethanol did not fall on the calculated line, and this was attributed to nucleophilic solvent assistance. The variation in AG, AH and AS (Fig. 21) can be reproduced remarkably well using ethane and the zwitterionic a-amino acid, glycine, as model compounds (Abraham et al., 1975 see also Abraham, 1974 Abraham and Abraham, 1974). 

Figure 48. Dependence of activation parameters for solvolysis of t-butyl chloride on mole fraction of water in ethyl alcohol + water mixtures at 298 K (Winstein and Fainberg, 1957), 4-184J = 1 cal.

Table 5-13. Rate constants and activation parameters for the SnI solvolysis of 2-chloro-2-methylpropane in six solvents at 25 °C [40],...

The results of solvolysis in acidic medium in comprehensive examination of methyloxirane, phenyloxirane, and their derivatives have been interpreted on the basis of activity parameters,Studies on the reactions of methyloxirane, 1,1-dimethyloxirane, and epichlorohydrin have led to the proposal of a new mechanism, denoted From research on dimethyloxirane in aqueous and non-... 

Quantitative data are available for the reaction of solvolysis of 1(2-tellurienyl)ethyl acetates in 30% ethanol.38,59 The first-order rate constants for the reaction at 60° of all the four congener systems, the activation parameters, the rates relative to the thiophene derivative (k/kTb), and the rates of the 3-methyl-substituted compounds relative to the corresponding unsubstituted derivatives (k Jkf,) are summarized in Table XIX. 

Rate Constants, Activation Parameters, and Relative Rates for the Solvolysis of I(2-Aryl)Ethyl Acetates in 30% Ethanol... 

M. Blandamer, J. Burgess, P. Duce, R. Robertson and J. Scott, A re-examination of the effects of added solvent on the activation parameters for solvolysis of f-butyl chloride in water, JCS Farad. Trans. 1,1981,77,1999-2008. 

The solvolysis of r-butyl chloride has been studied in a variety of solvents, and the activation parameters in Table P7-4 have been obtained at 25 0 [31]. 

Kinetic studies of aquation of [Fe(phen)3] and derivatives in binary aqueous media remain popular. A group additivity approach has been applied to aquation of [Fe(5N02phen)3] in aqueous alcohols (faster reaction) and formic and acetic acids (slower), to investigate its potential for mechanism diagnosis. Rate constants for dissociation of the parent complex increase tenfold on going from water to 100% dimethylformamide. Aquation rate constants and activation parameters have also been reported for the 5-nitro, 5-phenyl, and 4,7-diphenyl derivatives in water-dioxan mixtures. Both papers contain obscure discussions of solvolysis mechanisms in DMF-rich and dioxan-rich media. In the latter media it seems that ion pairs play a key role, as evidenced by activation entropies. The discussion of reactivities in terms of hydrophobicities of the complexes and their respective transition states represents a qualitative initial state-transition state analysis. An explicit analysis of this type has been published for the iron(II) complexes of the... 

Turning from the commonly studied tetrahedral compounds of tin to octahedral complexes, the kinetics of substitution at SnCl4py2 in nitrobenzene have been investigated. The activation parameters are reported to an astonishing precision the mechanism for solvolysis, as for chloride exchange, is said to be dissociative despite the very different rates reported for the two reactions. 

Table 10 Activation parameters for the solvolysis of trans-[Co(HL)(L)X2], where HL=MeC(NOH)C(NOMe)Me data from refs. 63 and 64)...

The stepwise solvolysis ofthe/rfl/w-[Co(dioxime)2(tu)a]+ions (dioxime = methyl-, dimethyl-, or methylpropyl-dioxime) has been studied, - and for the methyl-glyoxime complexes the rate constants and activation parameters for the two steps were resolved 10 A i = 10.0s = 23.5kcalmol S and AS = +7calK ... 

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