Activation parameters for substitution

Table 4.12 Activation Parameters for Substitution in Some Square-Planar Complexes in Water at 25 °C Refs. 149-152.

Only in a limited number of instances will the value of k and its associated parameters be useful in diagnosing mechanism. When the redox rate is faster than substitution within either reactant, we can be fairly certain that an outer-sphere mechanism holds. This is the case with Fe + and RuCP+ oxidation of V(II) and with rapid electron transfer between inert partners. On the other hand, when the activation parameters for substitution and redox reactions of one of the reactants are similar, an inner-sphere redox reaction, controlled by replacement, is highly likely. This appears to be the case with the oxidation by a number of Co(III) complexes of V(II), confirmed in some instanees by the appearance of the requisite V(III) complex, e.g. 

Table 8.12 Activation Parameters for Substitution Reactions of Ni°L. in Toluene at 25°C243...

Table 13 Rate constants and activation parameters for substitution ofV(CO)6i ...

Table 25.1 Activation parameters for substitution in selected square planar complexes (see Table 6.7 for ligand abbreviations).

TABLE 10.1 Activation Parameters for Substitution and Elimination Reactions ... 

Calculated from k, using the Eyring equation Chart 9.3 Activation parameters for substituted arylidenes [27]. 

A more detailed study of the hydration of phenylacetylene, 9a, and three substituted phenylacetylenes, p-methoxy 10, p-methyl 11, and p-chlorophenyl-acetylene 12, in aqueous sulfuric acid containing 5% ethanol has been carried out by Noyce and co-workers (19,20). The hydration obeys general acid catalysis and gives a linear Hq dependence. The slopes for the logarithm of the observed rate constants versus Ho and the activation parameters for the hydration of these phenylacetylenes are summarized in Table II. 

Table 7. Experimental Activation Parameters for Ring Expansion of Fluoro- and Methyl-Substituted Phenylnitrenes...

By analysis of nmr behavior Smallcombe and Caserio (1971) were also able to evaluate the rate+s of several other rapid substitution reactions (45)—(46) involving both Me2SSMe and the alkyldialkylthiosulfonium ion Me (SMe)2. The rate constants (at 40°) and activation parameters for these processes are shown below. Note that the rates of all these reactions are very fast. Comparison of k4 and k4S (or of k 4S and k4t) shows that, as would be... 

TABLE 6. Differential activation parameters for /i-cleavages of methyl-substituted benzyl carbinyloxy radicals in CCL4... 

Apart from ethyl acetate, the least reactive ester studied is N,0-diacetyl serinamide, which is hydrolyzed in a pH-independent reaction between pH 7 and 8 with a rate coefficient193 of 2.66 x 10-5 sec-1. Salmi and Suonpaa194 and Palomaa et al. 9S, have measured the rates of neutral hydrolysis of a number of chloroacetate esters, and this work has been extended more recently by Euranto and Cleve196-198, who have measured the activation parameters for the hydrolysis of several compounds. Motfat and Hunt199 have obtained the same data for the hydrolysis of a variety of alkyl and aryl trifluoroacetates, and the data for substituted phenyl acetates191 have been plotted in Fig. 14. Most of the available data are collected in Table 27. 

The determination that the cis and trans isomers of 1,2-d2-cyclopropane could be inter-converted thermally prompted experimental work on similar reactions exhibited by other substituted cyclopropanes to define activation parameters for representative instances of the isomerization and to begin to discriminate among alternative mechanistic suggestions. The 1,2-dimethyl- and 1-ethyl-2-methylcyclopropanes, for examples, were shown to approach cis, trans equilibrium with activation parameters log A, Ed (kcal mol"1) of 15.25, 59.4 and 15.08, 58.91 140. 

SECOND-ORDER RATE COEFFICIENTS (l.mole- .Sec- ) AT 25 °C AND ACTIVATION PARAMETERS FOR THE SUBSTITUTION OF DIALKYLMERCURYS BY MERCURIC IODIDE... 

Rate coefficients and activation parameters for the substitution of a number of dialkylmercurys are in Table 6. 

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