Radical stabilization energy application

Quantum chemistry provides a powerful tool for studying kinetic and mechanistic problems in free-radical polymerization. Provided a high level of theory is used, ah initio calculations can provide direct access to accurate values of the barriers, enthalpies, and rates of the individual reactions in the process, and also provide useful related information (such as transition structures and radical stabilization energies) to help in understanding the reaction mechanism. In the following, some of the applications of quantum chemistry are outlined. This is not intended to be a review of the main contributions to this field, nor is it intended to provide a theoretical account of reactivity in free-radical polymerization (108). Instead, some of the types of problems that quantum chemistry can tackle are described, with a view to highlighting the potential of quantum-chemical calculations as a tool for studying free-radical polymerization (see Radical Polymerization). 

This is only valid if A Ht s 35.6 kcal mol-1. It allows us to determine 2S °(R ) - 5E°(R—R) and so, to calculate BDE(C—C) and Ea. Moreover, if the heat of formation and therefore the stabilization energy of the dimer are known, one readily obtains the SE° and the heat of formation of the corresponding radical. The reverse is also obviously true. Three specific applications of Eq. (121) are given below ... 

Radicals derived from hydrofluorocarbons (HFCs) as well as hydrofluo-roethers (HFE) are often destabilized with respect to the methyl radical [51, 57,68,70,79-82], The low stability of these radicals implies that the C-H bonds in the corresponding closed shell parent compounds are comparatively strong and thus rather unreactive towards attack of oxidizing reagents. This latter property is of outstanding importance for the use of these compounds in a variety of technical applications, in which thermally stable, non-oxidizable, non-flammable compounds are needed. However, with respect to the environmental fate of these compounds high C-H bond energies... 

From the materials just mentioned earlier, one can conclude that mutual meta orientation (meta through a benzene) of the spin-bearing moieties is an indispensable condition for the existence of triplet states in aromatic di- or tri-(cation-radical)s. However, in fact, these systems have both singlet and triplet forms, and the questions are about what is the difference in the corresponding energy and which state is more stable. Stability of the polyion-polyradicals is also a very important factor, especially in the sense of practical application. Let us consider several relevant examples. 

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