Equal chemical reactivity

The kinetic treatment of polyreactions is greatly simplified by applying the principle of equal chemical reactivity. This principle assumes that the reactivity of a chemical group is independent of the size of the molecule to which it is attached. This postulated independence of rate constant from molecular size is already achieved at low degrees of polymerization, as can be seen, for example, by comparing the rate constants for the hydrolytic degradation of oligopolysaccharides (Table 15-5). Confirmation of the principle of equal chemical reactivity is also obtained from the polycondensation of dicarboxylic acids with diamines or diols and from free radical polymerizations. 

Since all like groups in polycondensations possess the same probability of reacting (principle of equal chemical reactivity), mixtures of different degrees of polymerization occur during polycondensation. In principle, the... 

It is frequently observed that Vmax and Km in enzymatic polyreactions are dependent on the degree of polymerization. This can be explained as follows 1. The binding strength of the nonreducing end of the sugar depends on the degree of polymerization, i.e., the principle of equal chemical reactivity... 

The principle of equal chemical reactivity applies, i.e., the propagation reaction rate constant is independent of molar mass. 

In these equilibrium reactions, not all glycol or acid molecules are converted into monoesters in the first step. If the reactivity of the individual hydroxyl and carboxyl groups is independent of the size of the molecules to which they are attached (the principle of equal chemical reactivity), then in the second step, in addition to molecules of degree of polymerization of 3 (SGS and GSG), new ones with degree of polymerization of 2 are simultaneously formed. In the third step, tetramers form from trimers and monomers or from two dimers, trimers from monomers and dimers, and dimers from two monomers, as well as, by this time, pentamers from dimers and trimers or monomers and tetramers, and hexamers from two trimers, etc., together with the original reactants formed by the reverse reactions. 

The kinetic treatment of polymerizations becomes much simpler if it is assumed that the reactivity of a group is unaffected by the size of the molecule to which it is attached (principle of equal chemical reactivity). This... 

The principle of equal chemical reactivity should be valid (see Section 16.4.3), so that the rate constant for the propagation reaction does not depend on the molecular weight. 

Discussion on any kind of polymers is logically preceded by at least a quick survey of properties of parent monomers. This is particularly relevant in the case of polysaccharides because monosaccharides are rather special monomers, with peculiar configurational-conformational properties and reactivity. Monosaccharides are multifunctional compounds, usually with three or four OH groups of approximately equal chemical reactivity reducing sugars have, of course, additional reaction capabilities. 

These descriptors have been widely used for the past 25 years to study chemical reactivity, i.e., the propensity of atoms, molecules, surfaces to interact with one or more reaction partners with formation or rupture of one or more covalent bonds. Kinetic and/or thermodynamic aspects, depending on the (not always obvious and even not univoque) choice of the descriptors were hereby considered. In these studies, the reactivity descriptors were used as such or within the context of some principles of which Sanderson s electronegativity equalization principle [16], Pearson s hard and soft acids and bases (HSAB) principle [17], and the maximum hardness principle [17,18] are the three best known and popular examples. 

Currently chemical reactivity is equal to the number of bonds which are not carbon-carbon single bonds. This is a crude approach to estimating the potential reactivity of i. We wish to calculate TV(r) for a newly discovered transform r based on reactions of precedent. Let IS(r) = the set of known transforms upon which the validity of r is to be based, then ... 

Thus, even if a bubble does not undergo transient collapse, extremely high temperatures and pressures are developed within the bubbles as they oscillate from R to R j. It is these large temperatures and pressures within the bubble which are thought to contribute to the significant increases in chemical reactivity observed in the presence of ultrasound. This does suppose however, that the reactant species is sufficiently volatile to enter the bubble. If it is not, increased chemical reactivity can only be assumed to have occurred due to increased molecular interaction within the liquid due to the large build up of pressure at the bubble wall. If the bubble is not to completely collapse then this will be equal to the liquid pressure at the liquid-bubble wall interface. 

From the investigation of all these data it is clear that the aromaticity of phosphinine is nearly equal to that of benzene. Their chemical reactivity, however, is different. Most important is the effect of the in-plane phosphorus lone pair, which (i) is able to form a complex and (ii) can be attacked by electrophiles to form A -phosphinines. Thus, electrophilic substitution reaction on the ring carbon is impossible. In Diels—Alder reactions, phosphinines behave as dienes, providing similar products to benzene but under less forcing condition (the reaction with bis(trifluoromethyl) acetylene takes place at 100 °C with 3, while for benzene 200 °C is required). 

The main aspects of the chemical reactivity of helicenes (e.g. electrophilic substitution) equally not deviate from those of planar aromatic compounds, and remarkable reactions of helicenes, which are incidentally found (e.g. the transannular bond formation between a C(l)-substituent and a part of the inner helix) can ultimately be reduced to known principles of aromatic reactivity. 

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