Concurrent reactions

A single species A (produced for example by radiolytic or photolytic means) may often disappear by concurrent first- (or pseudo first-) order (A ,) as well as by a second order process (2At2) already alluded to (Sec. 1.4.3). Thus 

At higher concentrations of A, the second-order process is more important and loss of A is second-order. As the concentration of A decreases, so the first term in (1.64) becomes dominant and decay of A is a purely first-order process (it may, for example, represent decomposition by solvent ) (Fig. 1.6). The rate curve may be analyzed by a relatively straightforward linearizing method. 

If a mixture of A and B undergoes parallel first-order or pseudo first-order reactions to give a common product C, and A and B do not interconvert readily compared with the reaction under study, 

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Scheme V shows a complex reaction in which a single reactant A undergoes independent, concurrent reactions to yield two different products.

The mechanism of benzylic bromination is similar to that discussed in Section 10.4 for allylic bromination of alkenes. Abstraction of a benzylic hydrogen atom generates an intermediate benzylic radical, which reacts with Br2 to yield product and a Br- radical that cycles back into the reaction to carry on the chain. The Br2 necessary for reaction with the benzylic radical is produced by a concurrent reaction of HBr with NBS. 

Ethanediol Sodium 3-(2-hydroxyethyl carboxylate)-5-carboxy- benzenesulfonate Studied as concurrent reaction to 151 ... 

Studied as a concurrent reaction to 123 Studied as a concurrent reaction to 124 Studied as a concurrent reaction to 238 Studied as a concurrent reaction to 238 Studied as a concurrent reaction to 238 Studied as a concurrent reaction to 244... 

Chain scission is the ultimate fate of a stressed bond. At some value below the critical stress for chain rupture, bond angle deformation may result in an increase in reactivity. As stated in Sect. 3.1, mechanically activated hydrolysis of polymers containing ester groups can lead to the scission of the bond this concurrent reaction should be differentiated from homolytic chain scission, for example by looking at any pH-dependence as was found to be the case during shear degradation of DNA [84]. 

In principle, there is also the possibility that concurrent reactions, with different kinetics, may proceed at more than one type of site or at different crystal faces. 

One very useful application arises when the desired reaction is difficult to measure kinetically. For example, imagine that the reaction of A) and B, the process of interest, does not produce an appreciable instrument signal under the concentration conditions the experiment requires. The reaction of A2 and B, however, can be coupled to it. If this second reaction is well characterized, with a known rate constant, and if P2 is easily detected, one can then study the concurrent reactions of A] and A2 with B. These will then provide the value of the otherw ise unknown k. Since B is limiting, [Pi ] = [B]o [P2]. thereby providing a value for the otherwise unmeasured concentration. With A2 known, the rate constant is... 

Competition reactions ad eosdem, 106 ad eundem, 105 (See also Reactions, trapping) Competitive inhibitor, 92 Complexation equilibria, 145-148 Composite rate constants, 161-164 Concentration-jump method, 52-55 Concurrent reactions, 58-64 Consecutive reactions, 70, 130 Continuous-flow method, 254—255 Control factor, 85 Crossover experiment, 112... 

In several systems studied the secondary ion is formed by more than one ion-molecule reaction. For example, we have found (43) that the NH4 + ion is formed in the ammonia system by the concurrent reactions ... 

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