First step is rate limiting

The crystal stmcture of the intermediate is not well understood. The final iron phase is termed superparamagnetic because the particle size is too small to support ferromagnetic domains. At low rates, the discharge occurs in two steps separated by a small voltage difference. At high rates, however, the two steps become one, indicating that the first step is rate limiting, ie, the second step (eq. 34) occurs immediately after formation of the intermediate (eq. 33). 

MNDO results suggest that the activation energies are similar for the gas phase thermal isomerization of isoxazole to oxazole via either a nitrile ylide or a keteneimine, through an azirine intermediate. The first step is rate limiting, which is in good agreement with experimental results (90JPO611). 

This represents the case where the first step is rate determining. (If this situation is known beforehand, one need not work through the steady-state approximation but merely write down dP/dt = k A since the first step is rate limiting and irreversible.)... 

Platz and coworkers performed computations that complete the rearrangement pathway for the fluoro-substituted nitrenes 21a-e by locating the transition states (24a-e) and product ketenimines (25a-e). The relative energies for these species are listed in Table 5.7. In all cases, the reaction proceeds by two chemical steps, passing through the intermediate azirine 23. For all of the cases examined except 21d, the first step is rate limiting. These computations are consistent with the experiment where the rate of formation of ketenimine equals the rate of disappearance for 21a-c, but for 21d, its rate of decay is faster than the rate of appearance of ketenimine 25e. 

Loss of CO from the stable, 18-electron Ni(CO)4 is slow relative to the addition of L to the more reactive, 16-electron Ni(CO)3. Consequently, the first step is rate limiting, and this mechanism has the following rate law ... 

Reaction energy diagrams for two hypothetical reactions. The rate-limiting step in each is determined by the difference in height between a low point and a subsequent high point. In (a), the first step is rate-limiting in (b), the second step is rate-limiting. 

At low pressnres or concentrations the first step is rate limiting and second order kinetics are observed. 

For a reaction with time-independent stoichiometry and a proposed reaction mechanism in which the first step is rate-limiting then the overall rate of reaction is determined by this first step and is not influenced by any of the following steps. 

In the El mechanism the leaving group departs before the proton is removed in a subsequent step. In common with the SnI reaction, the first step is rate-limiting, and results in the formation of an intermediate carbocation. Elimination, to form the neutral alkene, results if the carbocation is then deprotonated by a base... 

It is obvious that the rates of both electron transfers determine the steady state concentration of the oxy complex. The fact that benzphetamine greatly increases the first reduction step and also shows a high steady state concentration of the oxy complex may be in accordance with the latter concept. A varying oxy complex concentration would also indicate that both electron transfer steps proceed with similar velocities but that with some substrates the first step is rate-limiting and with others the second one. This interesting hypothesis deserves further substantiation. 

The first step is rate limiting, and has the rate law Rate = fei[Ni(CO)4]. Some ligand replacement reactions show more complicated kinetics. Study of the reaction... 

The first step is rate-limiting and requires high temperatures to be effective due to the high activation energy barrier with the designation Thermal NO. The third step is important in fuel-rich environments. 

The rate increases with the concentration of hypochlorite, temperature, and ionic strength. The solutions are most stable above pH 11, where the disproportionation rate is independent of pH. In this region, disproportionation is a two-step process. Since the first step is rate limiting, the rate is second order in hypochlorite ... 

Abstract. Nucleophilic addition of amines to olefins which are activated by electron withdrawing substituents occurs readily in aqueous dimethylsulfoxide. The reaction comprises two steps (1) nucleophilic addition to form a zwitterionic complex (2) removal of the ammonio proton of the zwitterion by a base. In most cases the first step is rate limiting but in some cases proton transfer is rate limiting. The latter situation prevails either when the reverse of the nucleophilic attack step is very rapid, as in the reaction of morpholine with benzylidenemalononitrile, or when the rate of proton transfer is depressed by a steric effect, as in the reaction of morpho-line with 1,l-dinitro-2,2-diphenylethylene. The steric effects in this latter system are among the most dramatic ones reported to date. Our data also show that the kinetic barrier to nucleophilic attack is substantially higher for nitro than for cyano activated olefins. This effect seems to be related to the well known fact that proton transfers involving nitro activated carbon acids are much slower than those of cyano activated carbon acids. 

If a step other than the first step is rate-limiting, the steps prior to the rate-determining step will play a role in determining the rate law, but any steps after the rate-limiting step will play no role in determining the forward rate. We illustrate this with the gas-phase reaction... 

We can summarize the rate-limiting step approximation If the first step is rate-limiting, the rate law is the rate law of the first step. If a step after the first step is rate-limiting, the rate law of the rate-limiting step is written. The concentrations of any reactive intermediates in the rate law of the rate-limiting step are replaced by expressions obtained by assuming that the steps prior to the rate-limiting step are at equilibrium. The result is the final approximate rate law. 

A computational study of the Baeyer-Villiger oxidation of benzaldehyde and acetaldehyde has been reported. Computational studies with peroxyacetic acid suggest that the first step is rate limiting and the addition of the peroxyacetic acid oxidation catalyst to the ketone carbonyl to produce the Criegee or tetrahedral intermediate (Scheme 163) "... 

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