Organic radical ions generation mechanisms

Degradation of organics by indirect ozone mechanism occiu s at basic conditions and involves generation of OH radicals and their further reaction with present organic compormds in water. Hydroxyl radicals are generated by the reaction of ozone with hydroxyl ions present in water [109] ... 

An organic disulfide sorbed into a transition-metal form of a zeolite may dissociate to give two thiol radicals. These may coordinate to cations by a mechanism which involves electron sharing or electron transfer, for example to oxidize the cation fiorther and to generate coordinated organic sulfide ions. This was observed with dimethyldisulfide sorbed into Co -exchanged zeolite... 

Additionally, there are features of organic electrochemistry that cannot be compared with organic chemistry because they are unique to this field and have no counterpart elsewhere in common chemistry. They result from the combination of electron transfer with a chemical reaction. This way reactive intermediates can be generated, which in another way are not or only in a limited extent accessible, such as radical ions. Mechanisms can be studied in otherwise not accessible depth from time-resolved electrical signals of starting materials, products, or intermediates (see Chapter 2) [6]. 

Many of the basic kinetic techniques of physical organic chemistry lose their usefulness when applied to radical reactions. Because of quantum-mechanical restrictions on spin multiplicity, reaction of a radical with a closed-shell molecule or ion generates another radical, with the radical species themselves being present in low concentration. For this reason, radical reactions are often chain reactions, whose kinetics are dominated by initiation or termination steps, with the rates of reactions generating most product frequently having little influence on the overall rate law. 

Most of the free-radical mechanisms discussed thus far have involved some combination of homolytic bond dissociation, atom abstraction, and addition steps. In this section, we will discuss reactions that include discrete electron-transfer steps. Addition to or removal of one electron fi om a diamagnetic organic molecule generates a radical. Organic reactions that involve electron-transfer steps are often mediated by transition-metal ions. Many transition-metal ions have two or more relatively stable oxidation states differing by one electron. Transition-metal ions therefore firequently participate in electron-transfer processes. 

The next topic of our consideration is the ion-radical incipiency. Generally, the mechanism of the ion-radical generation in frozen solution is as follows. Irradiation drives electrons out from a solvent. An organic precmsor (P) transforms into an ion-radical. At first glance, two reactions might be expected to take place electron capture (P -F e P ) and electron detachment (P + e P+ -F 2e). In fact, an indirect redox process takes place, with solvent participation. The example in Scheme 2.41 visualizes 2-methyltetrahydrofman (MeTHF) participation in the redox process, when P is a substance of electron affinity higher than that of the solvent. 

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