Kinetic data for substitution and

The ion Rh(H20) + is well characterized in aqueous solution from H2 0 exchange studies. The hydroxy species is more labile. There is an absence of pressure dependency measurements, but an mechanism is favored. 2-22 The formation and cleavage of some hydroxo-bridged rhodium(lll) and iridium(lll) eomplexes have been studied. Kinetic studies of oxidation by Rh(lll) indieate that RhOH2+ is the sole oxidant. 22 Kinetic data for substitution in Rh(N)5H20 + are sparse. An mechanism is favored for water exchange... 

Recent observations bearing on reactivity have usually been scattered and of uneven quality. We can add very few kinetic data on additions (equation 1) to those of a previous review on the other hand, kinetic data for substitutions (equation 2) are available. Studies of substituent, steric and solvent effects, which influence nucleo-philicity and electrophilicity orders as well as stereoselectivity, are limited and usually qualitative. For these reasons, we shall treat some of the large issues in this section and pick others up later in the context of specific nucleophiles. 

Table n. Enthalpic and kinetic data for substitution of Cr(CO)6 with olefins in heptane solution according to Scheme 2 ... 

We have seen ( 6.2.3) hat there is a close relationship between the rates of electrophilic substitutions and the stabilities of tr-complexes, and facts already quoted above suggest that no such relationship exists between those rates and the stabilities of the 7r-complexes of the kind discussed here. These two contrasting situations are further illustrated by the data given in table 6.2. As noted earlier, the parallelism of rate data for substitutions with stability data for o"-complexes is not limited to chlorination ( 6.2.4). Clearly, rr-complexes have no general mechanistic or kinetic significance in electrophilic substitutions. 

Chloroquinoline (401) reacts well with potassium fluoride in dimethylsulfone while its monocyclic analog 2-chloropyridine does not. Greater reactivity of derivatives of the bicyclic azine is evident also from the kinetic data (Table X, p. 336). 2-Chloroquinoline is alkoxylated by brief heating with methanolic methoxide or ethano-lic potassium hydroxide and is converted in very high yield into the thioether by trituration with thiocresol (20°, few hrs). It also reacts with active methylene carbanions (45-100% yield). The less reactive 3-halogen can be replaced under vigorous conditions (160°, aqueous ammonia-copper sulfate), as used for 3-bromoquino-line or its iV-oxide. 4-Chloroquinoline (406) is substituted by alcoholic hydrazine hydrate (80°, < 8 hr, 20% yield) and by methanolic methoxide (140°, < 3 hr, > 90% yield). This apparent reversal of the relative reactivity does not appear to be reliable in the face of the kinetic data (Tables X and XI, pp. 336 and 338) and the other qualitative comparisons presented here. 

Kinetic Data for Equatorial Ligand Substitution in Oxo Cyano and Related Complexes... 

In recent years, evidence has been found that both mechanisms of proton transfer can occur for certain intramolecularly hydrogen-bonded acids. Also, new kinetic behaviour has been obtained which allows a much more detailed examination of the reaction steps in (22). Kinetic data for the second ionization of substituted phenylazoresorcinols in the presence of hydroxide ions (25) were some of the first to be obtained for an intramolecularly hydrogen-bonded acid. The reciprocal relaxation time (t ) for the approach to equilibrium in a temperature-jump experiment was measured at different hydroxide-ion concentrations. A linear dependence of x on [OH] was obtained of the form of (26) (Eigen and Kruse, 1963 Inskeep et al., 1968 Rose and Stuehr, 1971). However, careful measurements at lower hydroxide-ion concentrations (Perlmutter-Hayman and Shinar, 1975 Perl-mutter-Hayman et al., 1976 Yoshida and Fujimoto, 1977) revealed that the... 

TABLE 8. Substrate oxidation potentials and kinetic data for the reaction of PINO with 4-X-substituted-iV,iV-dimethylanilines (X-DMAs), at 25 °C in MeCN solution ... 

A review has been made of the kinetic data for the substitution reactions of the Co(CN)5X 3 ions, where X refers to any one of various ligands. The evidence suggests that the penta-coordinate Co(CN)5 2 is generated as a reactive intermediate in the substitution of water in Co(CN)5OH2 2 by various nucleophiles and in the aquation of the various Co(CN)5X 3 ions. Preliminary studies indicate that the intermediate detected by the scavenger action of Br and SCN in the reaction of HN02 and Co(CN)5N3-3 is a different species than the one discussed above. 

Dale Margerum Ralph Wilkins has mentioned the interesting effect of terpyridine on the subsequent substitution reaction of the nickel complex. I would like to discuss this point—namely the effect of coordination of other ligands on the rate of substitution of the remaining coordinated water. However, before proceeding we should first focus attention on the main point of this paper-which is that a tremendous amount of kinetic data for the rate of formation of all kinds of metal complexes can be correlated with the rate of water substitution of the simple aquo metal ion. This also means that dissociation rate constants of metal complexes can be predicted from the stability constants of the complexes and the rate constant of water exchange. The data from the paper are so convincing that we can proceed to other points of discussion. 

Perhaps the most intriguing observation of helicenes is the unexpected ease with which these compounds racemize thermally. According to Martin 1031 three pathways for the thermal racemization can be considered 1) via bond breaking 2) via an internal double Diels-Alder adduct, and 3) via a direct inversion. Martin rejected the first possibility because it is not in accordance with kinetic data for the racemization. He could exclude the second possibility in an elegant way by using appropriately substituted derivativesl03>. 

KINETIC DATA FOR THE ACID-CATALYZED HYDROLYSIS AND FORMATION OF SUBSTITUTED BENZOATE ESTERS... 

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