Monomolecular consecutive reaction,

The reaction of (alkyl)chlorosilanes with a silica surface has been discussed and reviewed in great detail in literature [10], Although 5 different reactions are possible with di-, tri- or tetrachlorosilanes, basically two important surface species are created. The first is a monodentate silyl group, created by the monomolecular reaction of 1 silanol with 1 chlorosilane, according to reaction (A) (cfr. Figure 2). The second surface specie is a bidentate silyl group, created either by a bimolecular reaction (B) or by a consecutive reaction (C). We have reported previously [11] that the surface of MCM-48, prepared by the gemini 16-12-16 surfactant, possesses 0.9 OH/nm2. 

The binding of taxanes has been well characterized [10, 22] and shows a series of consecutive reactions involving a first fast bimolecular step (k+1 and k, ), a second slow monomolecular step (k+2, k 2) and a third step which is the structural change involving the change in the number of microtubule protofilaments. It can be proved numerically that the first bimolecular fast step of binding is diffusion controlled, thus indicating that taxanes can not directly bind to the lumenal site [22],... 

For a monomolecular reaction, f is 1. Using a bifunctional modifier of the type R2SiX2, f varies in the range 1-2, depending on the ratio of vicinal to free silanols. For a completely bimolecular reaction, where 2 silanol molecules react with one molecule of modifier, f=2. Trimolecular reactions are excluded for steric reasons. In the specific case of trichlorosilane, the monomolecular reaction with silica occurs according to (L). The resulting surface groups will be called primary species furtheron. Secondary species can be formed either by a true bimolecular reaction (O) or by a secondary (consecutive) reaction (M). 

The consecutive formation of o-hydroxybenzophenone (Figure 3) occurred by Fries transposition over phenylbenzoate. In the Fries reaction catalyzed by Lewis-type systems, aimed at the synthesis of hydroxyarylketones starting from aryl esters, the mechanism can be either (i) intermolecular, in which the benzoyl cation acylates phenylbenzoate with formation of benzoylphenylbenzoate, while the Ph-O-AfCL complex generates phenol (in this case, hydroxybenzophenone is a consecutive product of phenylbenzoate transformation), or (ii) intramolecular, in which phenylbenzoate directly transforms into hydroxybenzophenone, or (iii) again intermolecular, in which however the benzoyl cation acylates the Ph-O-AfCL complex, with formation of another complex which then decomposes to yield hydroxybenzophenone (mechanism of monomolecular deacylation-acylation). Mechanisms (i) and (iii) lead preferentially to the formation of p-hydroxybenzophenone (especially at low temperature), while mechanism (ii) to the ortho isomer. In the case of the Bronsted-type catalysis with zeolites, shape-selectivity effects may favor the formation of the para isomer with respect to the ortho one (11,12). 

Figure 1.7 An example of the interrelation of the bottleneck created by the rate-limiting step of a consecutive set of monomolecular transformations with the decrease in thermodynamic rushes of consecutive thermalized in intermediates Y. The stationary rate of the overall stepwise reaction here should be VE = 2(R P).

N. Bjerrum found the results did not agree with the velocity equation for monomolecular reactions but the results were better represented by velocity equations for two consecutive, bimolecular reactions, on the assumption that the reaction involves the sequence of changes [Cr(H20)4Cl2]Cl->[Cr(H20)5Cl]Cl2 ->[Cr(H20)e]Cl3. If x, y, z respectively denote the concentrations of these three salts, then dxjdt=—kix, and dxldt=k. It was found that at 25°, A i=0-C0272 -J-O-0000162/s, and A 2=(3I/s+0-005/s2)10—7, where s denotes the cone, of free hydrochloric acid. For soln. with M mols of dark green chromic chloride, the... 

It should be borne in mind that each activated monomer and polymer should only react with nonactivated monomer (addition polymerization) in both of these chemical examples. Reaction between an activated monomer and another activated monomer or a polymer (polycondensation) should not occur. With cyclophane, the mathematical treatment of the consecutive equilibria yields different expressions to those given in Table 16-1, since the /7-cyclophane, as initial monomer unit, yields two activated monomer molecules, and each reaction with activated monomer and its successive products yields only species with uneven numbers of structural elements. In addition, the polymerization of p-cyclophane is no longer a living polymerization when the degrees of polymerization are low, since, in this case, monomolecular (that is, intramolecular) termination reactions leading to the formation of inactive rings can occur. 

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