Reacting units

In the case of template polymerization, when reacting units are connected with the template by covalent bonds, analysis of the products can also be based on the separation of daughter polymer from the template. However, the covalent bonds should be broken for instance by hydrolysis of ester groups. This method was applied by Kammerer and Jung in order to prove that daughter polymer has the same number of units (plus end-groups) as the template. The scheme of the reaction can be represented as follows ... 

In a cycloaddition reaction, two sigma bonds are formed to give a new ring of atoms, and one classification of these reactions is based on the number of ring atoms thal derive from each of the reacting units. One of the simplest classes are (2 + 2 cycloadditions, such as... 

An interesting aspect of the coordination chemistry is the presence of S-S interactions. Electron transfer in Mo(SR)2 groups with partial disulfide formation is probably significant in biochemistry. Stiefel et al. have proposed a scheme with the reacting units (30a-c).110111... 

Furthermore, we can assume that the contributions to the activation energy of reaction from the substitution degree of reacting units are additive. Thus, the activation energy for the reaction between i substituted unit A and j substituted unit B (z,j=0,l) is... 

For simplicity, we start with a single tri-functional monomer RA3, the functional groups of which react with each other with the first shell substitution effect. It is now convenient to write down six types of reactions [44], one for each pair of reacting units of substitution degree 0,1, and 2. They are presented in Table 6 together with the appropriate rate constants. Similarly as in previous sec-... 

Table 6. The types of reactions in model polymerization of RA3 monomer with functional groups reacting with the first shell substitution effect. The subscripts at the symbols of reagents correspond to the codes of molecules (i,j-mers, see the text) and those at the rate constants indicate the degrees of substitution of reacting units. The left and right column corre-...

Real chemical reactions are violent affairs and quite unlikely to proceed as smoothly as the ideal metalization outlined before. Translational kinetic energy associated with reacting units is generally involved and only a fraction of activating encounters lead to binding. The final product is unlikely to incorporate all atoms promoted into the valence state smaller fragments are... 

This mechanism is more complex with respect to other vinyl polymer ones and demands specific simplifications. One proposed approach carefully analyses all the reactions of the single monomer unit in the polymer chain (Marongiu et al., 2003). The initial PVC polymer is simply represented by the chlorinated reference unit P (CH2CHC1)-P. The successive steps of degradation form polyene molecules and these species, which have different molecular weights, are represented by the alkene reference unit P-(CH = CH)-P. The reference species (reported in bold characters in the brackets) are the reacting units and are placed inside the polymer chain, represented here by the P at the beginning and end. 

In contrast to the preferred meta mode of intramolecular photoaddition of 5-phenyl-l-pentenes, where the alkene and benzene groups are separated by three atoms, irradiation of the styrene (64) yields a single stereoisomer of the ortho adduct (65). In (64), not only are the reacting units separated by 4 atoms, but also it is the styrene rather than the benzene which is excited. Comparable photoreactivity is seen for phenanthrene-styrene systems such as (66) which yield 2+2 adducts (67) along with products derived from competing Paterno-Btichi reaction of the ester carbonyl with the alkene side chain. The photochemical cycloaddition also proceeds in an intermolecular fashion between the ester of 9-phenanthrene carboxylic acid and para-methoxy-0-methylstyrene. The mechanism of this reaction is shown to involve addition of the styrene to the singlet excited state of the phenanthrene derivative. °... 

The equivalent weight (or the number of reacting units) depends on the chemical reaction. It may vary most often in redox reactions, when different products are obtained. 

In clinical chemistry, equivalents are frequently defined in terms of the number of charges on an ion rather than on the number of reacting units. Thus, for example, the equivalent weight of is one-half its atomic weight, and the number of equivalents is twice the number of moles. This use is convenient for electroneutrality calculations. We discuss equivalents in more detail in Section 5.3. 

The number of reacting units will depend on the reaction. These often vary in different redox reactions. 

Equivalents are based on the same concept as moles, but the number of equivalents will depend on the number of reacting units supplied by each molecule or the number with which it will react. For example, if we have one mole of HCl, we have one mole of to react as an acid. Therefore, we have one equivalent of H". If, on the other hand, we have one mole of H2SO4, we have two moles of the reacting unit and two equivalents of . The number of equivalents can be calculated firom the number of moles by... 

The equivalent weight is that weight of a substance in grams that will furnish one mole of the reacting unit. Thus, for HCl, the equivalent weight is equal to the... 

So remember that the number of reacting units of a compound, and hence the number of equivalents, will depend on the reaction it is undergoing. If A is the sample and T is the titrant. 

The equivalent weight of A is determined in the same way as it is for T that is, how many reacting units does A liberate or react with per molecule ... 

Since there are two reacting units per molecule of H2SO4, the normality of this solution will be twice its molarity ... 

The normality of the NaOH will be the same as its molarity, since it will consume one reacting unit per molecule ... 

Acid-Base. As we have mentioned, the reacting unit for acids and bases is the proton If the substance reacts as an acid, we must determine the number of reactive protons it possesses per molecule. If it reacts as a base, we must determine the number of protons it will react with per molecule. Then,... 

The number of reacting units (protons) depends on which reaction we choose. 

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