Product determining step

It may seem, at first sight, paradoxical that a competition reaction carried out under conditions in which the measured rate is independent of the concentration of the aromatic can tell us about the relative reactivities of two aromatics. Obviously, the measured rate has nothing to do with the rate of the product-determining step, and what is important in determining relative reactivities is the ratio of the values of ( 3.2.4) for two compounds. The criteria to be met for a correct application of the competitive method are well understood. ... 

In the Sakurai reaction, the product-determining step should be the nucleophilic addition of the allylsilane to the Lewis acid coordinated enone28. 

The existence of an ion pair stabilized by a solvent molecule in the product-determining step of the reaction has been established by calculations and also supported by the product composition (equation 89). While the formation of the diiodo derivative is characteristic of all the cited solvents, in tetrahydrofuran this iodination takes place with the predominant formation of l-iodomethyl-3-(4-iodobutoxy)adamantane (equation 89). 

Simple 1,2-additions to this compound have been observed123131132 also in other sulfenylation reactions, and in other electrophilic additions involving strongly bridged intermediates. Although these results have been interpreted as evidence that additions of sulfenyl halides to symmetrical alkenes do not involve open carbenium ions before the product-determining step, the different behavior observed in the case of 49 suggests123 that close proximity is necessary to have transannular participation of 7r-bonds, at least in additions of sulfenyl derivatives and of some other electrophiles carried out in the presence of efficient nucleophiles. 

Redman, E.W. Morton, T.H. Product-Determining Steps in Gas-Phase Breasted Acid-Base Reactions. D rotonation of 1-Methylcyclopentyl Cation by Amine Bases. J. Am. Chem. Soc. 1986,108, 5701-5708. 

PRODUCT-DETERMINING STEP PRODUCT DEVELOPMENT CONTROL Product formation,... 

Addition to alkene double bonds where the product-determining step usually occurs on the face opposite to the angular methyl groups ( a attack ). 

At the moment we have no good explanation for the observed acceleration except that it has a connection to the basic character of the quinuclidine part and the adsorption behavior of the cinchona molecule. In addition, we think that the rate and product determining steps occur on the platinum surface and that well defined interactions between the platinum surface (ensembles), one cinchona molecule and the a-ketoester are crucial. There are, of course, other possible explanations for the observed enantioselection. Wells and Thomas [80] have proposed that an array of... 

In the product-determining step of Scheme 6, the nucleophilic oxygen of water attacks one of the carbons this carbon then withdraws its orbital from the three-center bond and an ordinary a bond is formed between the remaining carbon and the hydrogen. 

The above definition of S is employed independently of the actual kinetic order of the product-determining step. Solvolytic reactions may be of higher kinetic order, or it could be argued that their kinetic order is ill-defined. There is no need to derive Equation 2.9 - it can stand alone as the definition of S. To illustrate how the equation works, suppose that the solvent is an equimolar mixture of alcohol and water, so the solvent mole ratio is 1.0. If the product mole ratio is also 1.0, then S = 1.0, and the product-forming reactions are unselective (so log S = 0 for an unselective reaction). If twice as much ether is formed as alcohol in an equimolar solvent mixture, then S = 2. In practice, many solvent compositions are employed, and the equation corrects automatically for variations in solvent composition. 

Substituents present in the starting material affected product composition according to a series of perceptions extracted from the outcome of the reaction of selected 2-phenyl-l,2,3-triazole 1-oxides with AcCl as illustrated in Scheme 120 (1981JCS(P1)503,1997BSB717). The reasoning is based upon initial formation of an O-acetylated species shown in the left column, which then reacts with acetate ion in the product-determining step. The O-acylated species may react in a similar fashion with other nucleophiles like the chloride ion. 

The product-determining step involves the partitioning of this intermediate between two paths one is the reaction with water and the other is loss of a proton ... 

The electronic nature of silylsilver intermediate was interrogated through inter-molecular competition experiments between substituted styrenes and the silylsilver intermediate (77).83 The product ratios from these experiments correlated well with the Hammett equation to provide a p value of —0.62 using op constants (Scheme 7.19). Woerpel and coworkers interpreted this p value to suggest that this silylsilver species is electrophilic. Smaller p values were obtained when the temperature of the intermolecular competition reactions was reduced [p = — 0.71 (8°C) and —0.79 (—8°C)]. From these experiments, the isokinetic temperature was estimated to be 129°C, which meant that the product-determining step of silver-catalyzed silylene transfer was under enthalpic control. In contrast, related intermolecular competition reactions under metal-free thermal conditions indicated the product-determining step of free silylene transfer to be under entropic control. The combination of the observed catalytically active silylsilver intermediate and the Hammett correlation data led Woerpel and colleagues to conclude that the silver functions to both decompose the sacrificial cyclohexene silacyclopropane as well as transfer the di-terf-butylsilylene to the olefin substrate. 

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