Chemical reaction homolytic dissociation

Chemical reactions may be divided into one of several categories depending on the extent to which overall bonding is maintained (Table 6-1). Reactions which lead to a change in the total number of electron pairs (bonds and non-bonded lone pairs) are at one extreme. Homolytic bond dissociation reactions provide an example. 

Homolytic dissociations. The dissociation of a diatomic molecule is probably the most simple of all chemical reactions thus the chlorine molecule Cl2 leads to atomic chlorine Cl ... 

In terms of tons of chemicals per year, this is by far the most important industrial process in which a light-induced reaction plays a key role. The photochemical reaction itself is extremely simple, being the homolytic dissociation of molecular chlorine, Cl2, into Cl atoms,... 

The most conventional kinetic scheme of FRP includes initiation, propagation, and bimolecular termination reaction steps. Additional reactions such as chain transfer are introduced to improve the process description. Free radicals are highly reactive chemical species produced by the homolytic dissociation of covalent bonds. Such species are produced through physical (thermoexcitation, radiation) or chemical methods (oxidation-reduction, addition, etc.). Generally, their survival time is less than a second, except for those radicals highly stabilized by specific chemical groups the hybridization state is sp. ... 

Radicals may be generated by thermal or photochemical processes that accomplish homolytic dissociation of a two-electron bond. Organic peroxides (equation 5.10) and azo compounds (equation 5.11) have weak bonds that undergo dissociation to radicals relatively easily. Chemical or electrochemical oxidation or reduction of stable molecules can produce radicals as well. One approach for generating ethyl radicals is to add triethylborane to a reaction mixture from which not all the oxygen has been removed. ° Radicals may also be produced by photoinduced electron transfer (Chapter 12). Single electron transfer processes initially generate radical... 

Quantum-chemical calculations by the method of Hartrii-Focks with parameters UHF and RHF 4-replaced 2,6-di-ferf.butylphenol values energy homolytic dissociation 0-H of communications - D jj are found Value energy formation and energy of homolytic cleavage D communications in molecules phenols depend on calculation approach M6 or PM3) and parameters of a method of Hartrii-Focks. There are dependences D from k reactions 4-substituted investigated 2,6-di-fert.butylphenol with iso-propylbenzene peroxide compound. Results of calculations D (Q of sterically hindered phenols in approach PM6 with parameter RHF are corrected to experimental data. 

Our current research centers on the development of a computational approach to model chemical reactions in aqueous solution, which has been a long-standing and almost formidable challenge within the realm of empirical models. The important step toward this goal is to build effective potential for water that can allow for autoionization and intermolecular proton and hydroxyl transfer. In addition, the ability to model water dissociation, both homolytically and heterolytically, can provide all the necessary reaction pathways under different conditions. 

Since homolytic or radical processes are largely governed by the effects of bond dissociation energies, a knowledge of BDE is required for the evaluation of chemical reactivity in such reactions. However, we have found, as we mention later, that BDE s are also an important factor influencing other types of reactions involving bond heterolyses. 

Some chemical additives can induce ion-radical formation and direct the reaction along the ion-radical route. The effect was discovered and studied in cases of nucleophilic substitutions of cumene derivatives (Kornblum 1975, 1982). Cumyl radicals are formed at the first step of substitution irrespective of whether a dissociative or homolytic cleavage takes place as a result of electron transfer to the cumene derivatives (Zheng et al. 1999). 

This chapter assesses the performance of quantum chemical models with regard to the calculation of reaction energies. Several different reaction classes are considered homolytic and heterolytic bond dissociation reactions, hydrogenation reactions, isomerization reactions and a variety of isodesmic reactions. The chapter concludes with a discussion of reaction energies in solution. 

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