Rate-determining slow step

Because of thetr electron deficient nature, fluoroolefms are often nucleophihcally attacked by alcohols and alkoxides Ethers are commonly produced by these addition and addition-elimination reactions The wide availability of alcohols and fliioroolefins has established the generality of the nucleophilic addition reactions The mechanism of the addition reaction is generally believed to proceed by attack at a vinylic carbon to produce an intermediate fluorocarbanion as the rate-determining slow step The intermediate carbanion may react with a proton source to yield the saturated addition product Alternatively, the intermediate carbanion may, by elimination of P-halogen, lead to an unsaturated ether, often an enol or vinylic ether These addition and addition-elimination reactions have been previously reviewed [1, 2] The intermediate carbanions resulting from nucleophilic attack on fluoroolefins have also been trapped in situ with carbon dioxide, carbonates, and esters of fluorinated acids [3, 4, 5] (equations 1 and 2)... 

True/False. You can get a rate law directly from the rate-determining (slow) step in a mechanism. 

Even though the Paal-Knorr pyrrole synthesis has been around for 120 years, its precise mechanism was the subject of debate. In 1991, V. Amarnath et al. investigated the intermediates of the reaction and determined the most likely mechanistic pathway. The formation of pyrroles was studied on various racemic and meso-3,4-diethyl-2,5-hexanediones. The authors found that the rate of cyclization was different for the racemic and meso compounds and the racemic isomers reacted considerably faster than the meso isomers. There were two crucial observations 1) the stereoisomers did not interconvert under the reaction conditions and 2) there was no primary kinetic isotope effect for the hydrogen atoms at the C3 and C4 positions. These observations led to the conclusion that the cyclization of the hemiaminal intermediate is the rate-determining (slow) step. 

The rate equation can be described using only the concentration of the halide and not that of the nucleophile. The rate determining (slow) step is ionization of the C—Br bond and the fast second step does not greatly influence the overall rate. The rate expression is. Rate = k [RX], for this unimolecular reaction. 2... 

The simplest mechanism that can be put forward which covers these points is one where the rate-determining slow step is the opening of a chloride bridge bond. Coordination of a diene at the vacant site thus created and the subsequent H-transfer reaction to give the enyl complex are then expected to be very fast. 

Simplification of the rate expression is possible if the rate constants corresponding to one of the elementary steps in the reaction mechanism can be identified as being small compared to others. This is called the slow step or the rate-controlling/rate-limiting/rate-determining step in the overall reaction mechanism. In the limiting case, all elementary reaction steps of the mechanism are essentially at equilibrium except the rate-determining slow step therefore, the net steady-state rate can be expressed in terms of the slow step, and equilibrium statements can directly be written for all other steps in the mechanism. 

The experimental rate is found to depend on the concentrations of the complex ion and on OH. One postulated mechanism includes as the rate-determining (slow) step this dissociation of the conjugate base of the complex ion,... 

You write the rate equation for the rate-determining (slow) step, just as in the previous example. In this case, however, the equation contains a species, N2O2, that does not appear in the overall equation for the reaction. You need to eliminate it from the final form of the rate law. Note that the first step is fast and reaches equilibrium. You use this fact to write an expression for [N2O2]. Then you substitute this expression for [N2O2] into the rate equation. 

Solution. The decomposition of the primary complex ES to the free enzyme E and the product P is assumed to be the rate-determining (slow) step. The expression below is valid for both homogeneous (where the enzyme is used in the native or soluble form) and for immobilized enzyme reactions. The reaction rate v is given by ... 

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