Bimolecular control principles

Bimolecular Reactions. Models of surface-catalyzed reactions involving two gas-phase reactants can be derived using either the equal rates method or the method of rate-controlling steps. The latter technique is algebraically simpler and serves to illustrate general principles. 

In principle, these approaches are very attractive because they probe multiple pathways in the critical regions where the pathways are separated, but in practice these are extremely challenging experiments to conduct, and the interpretation of results is often quite difficult. Furthermore, these experiments are difficult to apply to bimolecular collisions because of the difficulty of initiating the reaction with sufficient time resolution and control over initial conditions. 

Intracluster reactions are often induced by photons, as discussed in several chapters in this volume. One reason for the strong interest in such processes is that the relative geometries of the reagents are dictated by the cluster geometry so that one can, in principle, control the stereochemistry between them as if carrying out bimolecular collisions with oriented reactants (Wittig et al. 1988). 

Scheme 21 (related to Scheme 20, plus monomer conversion) describes, in principle, CRP. Disappearance of A by bimolecular termination in the radical process (termination) could also be unimolecular, in, for example, controlled cationic polymerization. 

The number average molar mass, Mn, and molar mass distribution (MMD) are controlled by interplay of kinetic parameters, which will be described in more detail in Chapter 5. In principle there are two ways of terminating a growing chain bimolecular termination and transfer. These two modes of termination have led to the two main categories of living radical polymerization (a) reversible termination and (b) reversible chain transfer. 

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