Exchange reactions, rate

Complexation constants of crown ethers and cryptands for alkali metal salts depend on the cavity sizes of the macrocycles 152,153). ln phase transfer nucleophilic reactions catalyzed by polymer-supported crown ethers and cryptands, rates may vary with the alkali cation. When a catalyst 41 with an 18-membered ring was used for Br-I exchange reactions, rates decreased with a change in salt from KI to Nal, whereas catalyst 40 bearing a 15-membered ring gave the opposite effect (Table 10)l49). A similar rate difference was observed for cyanide displacement reactions with polymer-supported cryptands in which the size of the cavity was varied 141). Polymer-supported phosphonium salt 4, as expected, gave no cation dependence of rates (Table 10). 

Isotopic exchange reaction rates and oxygen diffusion coefficients of Pt/M-CZ, S-CZ and R-CZ at 41 are listed in Table V (Dong et al., 2004a). The surface diffusion rate for R-CZ (Rg) is nearly 4 times larger than the bulk diffusion rate or the equilibrium isotopic exchange rate (R ), while it is... 

Table 22 Dependence of the Oxygen vs. Chlorine Exchange Reaction Rate upon the n Character of the P=0 Bond ...

The relative reactivity of different positions toward electrophilic substitution is conveniently studied by acid-catalyzed deuterium exchange reaction rates can be followed by NMR and introduction of deuterium hardly affects the reactivity of the remaining positions. In D2S04 both quinoline and quinoline 1-oxide react as the conjugate acid at positions 8 > 5, 6 > 7 > 3. 

Changes with time in the isotopic exchange reaction rate between H2 and HDO(v) over a hydrophobic Pt-catalyst induced by the addition of HN03 were studied experimentally The HN03 poisoning was found to be reversible and was well explained in terms of the competitive adsorption of HNO, with H2 or HDO onto the catalytic active sites. The adsorption equilibrium for HN03 could be expressed by the Frumkin-Temkin equation and the time evolution of the activity was well expressed by the Zeldovich rate equation. 

HL Theory of pressure effects on outei sphere self-exchange reaction rates... 

It should be briefly mentioned here that temperature and solvent changes may help to circumvent problems arising if the process under study occurs with a rate comparable to the time scale of the NMR instrument. In such a case, cooling leads to slow exchange (case 1), while heating increases the exchange reaction rate (case 2). Similarly, a less competitive solvent usually slows down the process (case 1), while a more competing one accelerates it (case 2). 

On the other hand, the surface exchange reaction rates (as denoted by eqn (18.1)) integrated with all the sub-steps on the upstream and the downstream sides may be written, respectively, as ... 

Reverse surface exchange reaction rate constant... 

Molar flow rate of air feed and the sweep gas Oxygen permeation rate Reverse surface exchange reaction rate constant... 

ISM can also be applied to the calculation of electron exchange reaction rates of coordination compounds and aquo-metal ions [60,62]. Table 10 presents some of the calculated data with the force constants estimated through eqs(38) and (41), with a coordination number of 6. The n values are identical to the order of the reactive bonds in reactants and products. In contrast with the theory of Marcus, our model provides calculated rates within an order of magnitude of experiment [60]. 

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