Nature of Organic Ion-Radicals and Their Ground-State Electronic Structure

Organic chemistry represents an extensive volume of facts from which the contemporary doctrine of reactivity is built. The most important basis of this doctrine is the idea of intermediate species that arise along the way from the starting material to the final product. Depending on the nature of chemical transformation, cations, anions, and radicals are created midway. These species are formed mainly as a result of bond rupture. Bond rupture may proceed heterolytically or homolytically R-X - R + X+, R-X R+ + X , or R-X R + X.  

Ions or radicals formed from a substrate further react with other ions or radicals. There are many reactions that include one-electron transfer before the formation of ions or radicals. Sometimes, electron transfer and bond cleavage can take place in a concerted manner. The initial results of one-electron transfer involve the formation of ion-radicals. 

This book focuses on species of the type (RX)-, that is, on cation- and anion-radicals. These terms were first introduced by Weitz (1928) ( Kationradikale and Anionradikale ). Currently, organic chemists differentiate that the anion-radicals originate from n and o acceptors and the cation-radicals originate from n, a, or n donors. These species are formed during reactions, when an organic molecule either loses one electron from the action of an electron acceptor or acquires one from the action of an electron donor R—X - e — (R—X)+ or R—X + e — (R—X).  

The concept of molecular orbitals (MOs) helps to explain the electron structure of ion-radicals. When one electron abandons the highest occupied molecular orbital (HOMO), a cation radical is formed. HOMO is a bonding orbital. If one electron is introduced externally, it takes the lowest unoccupied molecular orbital (LUMO), and the molecule becomes an anion-radical. LUMO is an antibonding orbital. Depending on the HOMO or LUMO involved in the redox reaction, organic donors appear as n, a, or n species, whereas organic acceptors can be tt or a species. Sometimes, a combination of these functions takes place. 

Ion-radicals have a dual character. They contain an unpaired electron and are, therefore, close to radicals. At the same time, they bear a charge and are, naturally, close to ions. This is why the words ion and radicaf are connected by a hyphen. Being radicals, ion-radicals are ready to react with strange radicals. Like all other radicals, they can dismutate and recombine. Being ions, ion-radicals are able to react with particles of the opposite charge, and are prone to form ionic aggregates. In contrast to radicals, the ion-radicals are specially sensitive to medium effects. 

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I Nature of Organic Ion-Radicals and Their Ground-State Electronic Structure... 

After reviewing the nature of organic ion-radicals and their ground-state electronic structure, the book discusses their formation, the relationship between electronic structure and reactivity, mechanism and regulation of reactions, stereochemical aspects, synthetic opportunities, and practical applications. Additional topics include electronic and optoelectronic devices, organic magnets and conductors, lubricants, other materials, and reactions of industrial or biomedical importance. 

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