bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Radicals byEPR
Authors: Walton John C. 
Published: March 2012

AbstractThis article explains why electron paramagnetic resonance (EPR) spectroscopy is one of the most versatile and useful techniques for investigating free radicals. Easy to use EPR tools are expounded for organic chemists to exploit in researching the structures and reactivities of radicals and as a resource for synthetic planning. The article provides key references and introduces the literature on the EPR spectra of a wide range of organic radicals in solution. How EPR spectra result from molecules containing one unpaired electron (UPE) is explained and basic theory is presented for isotropic conditions. A correlation chart enablesg‐factors, which are key spectral parameters, to be used in determining which element is the principal site of the UPE. Methods of analysing complex EPR spectra and obtaining hyperfine splittings (hfs) are described. How geometries around the central atoms of radicals, and conformations about neighboring bonds, can be deduced from EPR data is explained. Modernab initiomethods of computing EPR parameters are briefly sketched. Features of the EPR spectra of model radicals centered on elements from groups 13, 14, 15, and 16 of the periodic table are surveyed. EPR methods for concentration measurements and for studying radical kinetics in time‐resolved and steady‐state modes are set out. Derivations from EPR spectral data of thermodynamic parameters such as radical enthalpies of formation and bond dissociation enthalpies are also explained.
Radical Stability—Thermochemical Aspects
Authors: Hioe Johnny , Zipse Hendrik 
Published: March 2012

Abstract
Reaction enthalpies for hydrogen transfer reactions provide a quantitative basis for the definition of the stability of C‐, S‐, O‐, N‐, and B‐centered radicals. The radical stabilization energies (RSEs) obtained in this way reflect the influence of the substitution pattern on the unpaired spin as well as ground state effects in the respective closed shell parent systems. The combination of theoretically calculated RSEs with experimentally measured bond dissociation energy (BDE) data allows for the construction of global stability scales for radicals of different type and thus the opportunity to predict reaction energies for a wide range of hydrogen transfer reactions.
Radical Cation/Anion and Neutral Radicals: A Comparison
Authors: Hancock Amber N. , Tanko J. M. 
Published: March 2012

Abstract
This article examines similarities between radical and radical ion reactions. Radicals and radical ions have worked there way into almost every facet of mainstream chemistry over the past 60 years. The importance as well as usefulness now associated with the reactions of radicals is in stark contrast to their prior role as poorly understood scapegoat molecules often blamed for failed reactions. The processes discussed herein demonstrate two critically important concepts to the radical chemist: (i) kinetic studies are an excellent and versatility applicable tool to determine mechanistic data for chemical reactions and (ii) published mechanistic data for more thoroughly studied radical processes have provided and continue to provide key insight into the factors governing reactivity and mechanism of their charge bearing counterparts.
Atmospheric Radical Chemistry
Authors: Wine Paul H. , Nicovich J. Michael 
Published: March 2012

Abstract
The atmosphere is a complex photochemical reactor where a vast majority of the chemical transformations involve reactions of reactive free radicals that are generated by solar photolysis of stable precursors. This article focuses on radical chemistry in the lowest 50 km of the atmosphere, an altitude regime that contains about 99.9% of the atmospheric mass. The altitude regime of interest is divided into two layers, the lower altitude troposphere that contains about 85% of the atmospheric mass, and the higher altitude stratosphere. The stratosphere contains 90% of all atmospheric ozone, and this ozone protects the earth's biosphere from the harmful effects of ultraviolet radiation. Hence, our discussion of stratospheric chemistry focuses on radical‐catalyzed pathways for ozone destruction. Tropospheric radical chemistry is extremely complex, owing largely to the presence in the troposphere of a multitude of organic compounds that are too short‐lived to be transported to the stratosphere. Our discussion of tropospheric radical chemistry focuses on the complex chain reactions involving ozone, hydroxyl radicals, nitrogen oxide radicals, and organics that maintain the oxidizing power of the troposphere, that is, the ability of the troposphere to cleanse itself of pollutants.
Basic Concepts on Radical Chain Reactions
Authors: Sherburn Michael S. 
Published: March 2012

Abstract
This article serves as an introduction to basic concepts in radical chemistry and is written in the form of a tutorial review. The intention is to provide the reader with the necessary fundamental information on structure, reactions, and mechanism to permit a basic understanding of the radical chemistry in the articles that follow. The content is based upon undergraduate and postgraduate courses in synthetic free radical chemistry taught over the past 15 years by the author. The material is presented into two sections. The first serves as a primer on radical structure and reactivity, on discrete processes involving radicals, and on how these radicals and discrete processes are sequenced into chain reactions. The second section extends the concepts of the first and introduces the major classes of radical chain reactions.
Radical Cascade Reactions
Authors: Baralle Alexandre , Baroudi Abdulkader , Daniel Marion , Fensterbank Louis , Goddard Jean‐Philippe , Lacôte Emmanuel , Larraufie Marie‐Hélène , Maestri Giovanni , Malacria Max , Ollivier Cyril 
Published: March 2012

AbstractThis article deals with the recent developments in radical cascade reactions with a special emphasis on their applications in natural product synthesis. Particular attention has been paid to the mechanisms of the cascade sequences and the involvement of original elementary steps. Section 2 is dedicated to cascades occurring via a purely radical chain mechanism, describing first intramolecular processes, then processes involving both inter‐ and intramolecular steps. Section 3 is devoted to cascade reactions combining radical and ionic steps. The reactions are classified according to the type of metal reagent used, such as, samarium, titane, manganese, cerium, iron, zinc, silver, and copper. In addition, newer developments in radical cascades triggered by visible light photoredox catalysis are discussed.
The S
RN
1 Reaction
Authors: Bardagí Javier I. , Vaillard Victoria A. , Rossi Roberto A. 
Published: March 2012

Abstract

Since its discovery, the radical nucleophilic substitution, or S
RN
1 reaction, has been widely used to achieve new CC or C‐heteroatom bonds. The mechanism involves a chain propagation cycle with radicals and radical anions as intermediates. The initiation step is an electron transfer to a substrate to form its radical anion, which fragments to afford a radical and the anion of the leaving group. The radical thus formed couples with a nucleophile to give a new radical anion which, in the next propagation step, transfers its extra electron to the substrate, closing the cycle.

Here we discuss S
RN
1 reactions of aromatic substrates with carbanions and heteroaromatic nucleophiles as well as ring‐closure reactions to obtain heterocycles by different approaches.

S
RN
1 reactions of vinylic halides with nucleophiles and the competing mechanisms are also examined. Reactions of aliphatic substrates that do not react or are poorly reactive toward polar nucleophilic substitutions (cycloalkyl, bridgehead, neopentyl, and perfluoroalkyl halides) are discussed in terms of mechanistic requirements to follow an S
RN
1 process. In addition, the reactions of alkyl substrates with electron‐withdrawing groups also are presented.

Every year, new synthetic strategies and mechanistic studies involving S
RN
1 reactions are reported, which constitute a useful tool in the field of organic chemistry.
Radicals and Carbohydrates
Authors: Pérez‐Martín Inés , Suárez Ernesto 
Published: March 2012

Abstract

This article reviews the progress in the area of radicals in carbohydrate chemistry with special attention to new developments published during the past decade. No attempt has been made to present a comprehensive review of the literature but, rather, some specific examples are given to highlight the most synthetically valuable processes. The major focus is on inter‐ and intramolecular carbon–carbon bond‐forming radical reactions, with emphasis on the preparation of
C
‐glycosides,
C
‐ketosides,
C
‐disaccharides, and branched‐chain sugars, as well as on the synthesis of polyfunctionalized carbocycles by radical cyclization of acyclic carbohydrate derivatives. We also describe methods for the formation of carbon–hydrogen bonds, and synthesis in which a heteroatom‐centered radical plays a clear role in the carbon–heteroatom (C–N, C–P, C–O, C–S/Se, and C–Br) bond formation. Finally, a few selected examples of alkoxyl radical β‐fragmentation reactions, carried out under oxidative or reductive conditions, are included to illustrate their potential in the preparation of chiral synthons.
Electrochemically Initiated Radical Reactions
Authors: Bohn Martin A. , Paul Anna , Hilt Gerhard 
Published: March 2012

Abstract
This article reports on the applications of electrochemistry for the generation of radicals as neutral, cationic, and anionic intermediates and their use in preparative reactions for the formation of carbon–carbon and carbon–heteroatom bonds. The focus of this article is on electrochemical oxidation reactions of enol ethers, ketene acetals, and electron‐rich aromatic compounds. Furthermore, recent advances in the electrochemically induced synthesis of four‐membered ring systems and biaryl compounds are covered. The oxidative carbon–carbon bond formation by Kolbe electrolysis concludes the section dealing with oxidative transformations. The section describing reductive processes consists of indirect electrochemical reduction of alkylhalides and thioesters, as well as the reductive interconversion of functional groups described recently.
Radical Rearrangements: Ester‐Substituted Radicals and Hydrogen Atom Migrations
Authors: Sasaki Kaname , Cumpstey Ian , Crich David 
Published: March 2012

Abstract
This article covers radical rearrangements that do not involve the redistribution of the carbon skeleton of the substrate. The focus is on the rearrangement of ester‐substituted radicals and on hydrogen atom abstractions, and the emphasis is on the radical rearrangements themselves rather than on their application in synthesis, which is left to the imagination and creativity of the practitioner.
Manganese(III) Acetate,CAN, andFe(III) Salts in Oxidative Radical Chemistry
Authors: Burton Jonathan W. 
Published: March 2012

AbstractThis article provides a broad overview of oxidative radical methods for the formation of CC bonds using manganese(III) acetate, cerium(IV) ammonium nitrate, and various iron(III) salts. The article begins with a discussion of the various general mechanisms encountered in oxidative radical chemistry and then provides an overview of inter and intramolecular CC bond‐forming reactions. The oxidative radical chemistry of β‐dicarbonyl and related compounds forms a major part of the article. Comparison of the three metals is made whenever possible as well as highlighting reactions which are specific to, or higher yielding with, one particular metal. The discussed synthetic methodologies are illustrated with examples of complex molecule synthesis.
Oxidatively Formed Sugar Radicals in Nucleic Acids
Authors: Gimisis Thanasis , Chatgilialoglu Chryssostomos 
Published: March 2012

AbstractThis article focuses on the chemistry of sugar radicals in the context of oxidative damage in nucleic acids. The seven sp3‐hybridized CH bonds in 2‐deoxyribose (six in ribose) are attacked by reactive oxygen species, generated either by the cell's internal oxygen cycle or by environmental insults, by chemical nucleases including enediyne antibiotics and reactive metal complexes, to generate sugar nucleosidyl radicals. For each position on the 2‐deoxyribose or ribose moiety, the factors leading to the generation of the specific sugar radical, together with its fate under aerobic or anaerobic conditions in the nucleoside, nucleotide, single‐stranded oligonucleotide, or double helix DNA, are discussed. Furthermore, the model systems that have been constructed for the photochemical‐independent generation of each nucleosidyl radical or DNA lesion are described, together with the biochemical studies that have been performed in order to elucidate the stability, reparability, and mutagenic potential of each lesion. Other biologically important events involving modification of nearby nucleobases and the formation of DNA–DNA and DNA–protein cross‐links are also discussed.
Radical‐Based Damage of Sulfur‐Containing Amino Acid Residues
Authors: Schöneich Christian 
Published: March 2012

Abstract

The reactions of biologically relevant free radicals with S‐ and Se‐containing amino acids are reviewed with regard to amino acid reactivity, the nature of product radicals, and ensuing radical reactions. Emphasis is placed on the formation and reactions of thiyl and selenyl radicals as well as radical cations from sulfides and selenides. The reactions of thiols with carbon‐centered radicals, superoxide, nitrogen monoxide, nitrogen dioxide, and tyrosyl radicals are covered as well as the reactions of thiyl radicals with oxygen. Reversible
intra
‐ and
inter
molecular hydrogen transfer reactions of thiyl radicals are discussed in view of recent experimental and theoretical data. One‐electron oxidation reactions of sulfides are reviewed especially with regard to the stabilization of sulfide radical cations through heteroatom‐containing substituents, which are present in peptides and proteins. The relevance of these radical reactions for protein oxidation under conditions of oxidative stress is discussed.
Lipid Peroxidation
Authors: Niki Etsuo 
Published: March 2012

AbstractFree and ester forms of fatty acids and cholesterol are physiologically important lipids. They are oxidized by free radicals to give diverse products. Above all, polyunsaturated fatty acids having more than two double bonds and their esters are quite susceptible to free radical attack and oxidized by chain mechanism. These lipids are oxidized also by nonradical oxidants such as ozone and singlet oxygen and by enzymes such as lipoxygenase, cyclooxygenase, and cytochromeP450 to produce specific products. The free‐radical‐mediated oxidation of lipids, often referred to aslipid peroxidation(LPO), proceeds bothin vitroandin vivo. LPO has been shown to induce disturbance of membrane organization and functional loss and modification of proteins and DNA bases, and LPO has been implicated in the pathogenesis of various diseases. Therefore, the role of antioxidants that inhibit LPO has received much attention. At the same time, LPO products have been shown to act as a redox signaling mediator. Although many LPO products exert cytotoxicity, sublethal concentrations of LPO products induce cellular adaptive response and enhance tolerance against subsequent oxidative stress through upregulation of antioxidant compounds and enzymes. Such opposite dual functions of LPO products imply that LPO may exert both deleterious and beneficial effectsin vivo. The levels of LPO products are assumed to be a biomarker of oxidative stressin vivo. The literatures show that the levels of LPO products in plasma of healthy human subjects are below 1 μM and that the molar ratios of LPO products to the respective parent lipids are below 1/1000, that is, below 0.1%. Numerous data show that the levels of LPO products in human fluids and tissues increase with a progress of various diseases.
Antioxidants in Chemistry and Biology
Authors: Valgimigli Luca , Pratt Derek A. 
Published: March 2012

AbstractAntioxidants are omnipresent in nature and industry; they are used to slow down the autoxidative degradation of both organic tissues and petroleum‐derived products. Various mechanisms by which antioxidants can act are known, the most common of which are introduced here. Since autoxidation is a radical chain reaction, radical‐trapping antioxidants play a particularly important role; therefore, we will discuss these compounds in most detail. To introduce and develop central concepts relating to this topic, we present kinetic and thermodynamic data obtained for the reactions of phenols, the archetypical radical‐trapping antioxidants, with chain‐carrying peroxyl radicals, and describe the means to obtain these data. We then extend our discussion to other important classes of radical‐trapping antioxidants, beginning with the closely related polyphenols and newly developed pyridinol and pyrimidinol antioxidants, and then further to aromatic amines, organosulfur compounds, and their derivatives. We go on to touch upon the synergistic behavior in antioxidant combinations, and the effects of the medium on these interactions, and finally round things up with a few more important biological examples: ascorbate and β‐carotene. A few comments on the state of the field and areas requiring further research and development are included.
Nitroxide‐Mediated Polymerization and its Applications
Authors: Gigmes Didier , Marque Sylvain R. A. 
Published: March 2012

AbstractIn this survey, the fundamental aspects of nitroxide‐mediated polymerization (NMP) and the importance of each step/stage in its fate are discussed. The factors controlling the homolysis, reformation, and side‐reactions of alkoxyamines are presented. The various types of NMP—bulk, solution, aqueous, emulsion, miniemulsion, andin situ—are exemplified. The synthesis of advanced polymers by NMP is presented.
Photoinduced Reactions of Radical Ions via Charge Separation
Authors: Fukuzumi Shunichi , Ohkubo Kei 
Published: March 2012

AbstractThis article describes the recent development of photocatalytic reactions using a simple donor‐acceptor‐linked dyad, 9‐mesityl‐10‐methylacridinium ion (Acr+–Mes). The electron‐transfer state of Acr+–Mes (Acr·–Mes·+), produced on visible light irradiation, acts as an efficient oxidant and reductant. The use of Acr+–Mes, which has an extremely long‐lived charge‐separated state, enables the construction of highly efficient photocatalytic systems such as oxygenation, bromination, and carbon‐carbon bond formation of aromatic compounds.
Conducting Polymers: Applications in Electronics and Photovoltaics
Authors: Dong Huanli , Hu Wenping 
Published: March 2012

Abstract
The discovery of conducting polymers in 1970s shocked the world and then evoked increasing research interests from laboratory to technology because of their particular physical properties as well as the feasible solution‐processed superiority in potential low‐cost, large‐area optoelectronic devices. Following the report of first‐generation conducting polymer material, doped polyacetylene, remarkable progresses have been made in the development of novel conjugated polymers with reasonable functionality and demanding molecular architectures through molecular tailoring leading to various desired molecular electronic and optical applications. Among them, polymer‐based light‐emitting diodes (PLEDs), polymer‐based field‐effect transistors (PFETs), and polymer‐based solar cells (PSCs) are the most representative application fields and have undergone great progress, especially in the past decade. The aim of this article is to introduce briefly recent breakthrough improvement of conjugated polymers in these areas with an emphasis on some important and representative conjugated polymers in device applications as well as the principle of optimization approaches.
A Paradigm for the Radical‐Mediated Photochemical Synthesis of Metal Nanostructures
Authors: Scaiano Juan C. , Stamplecoskie Kevin G. , McGilvray Katherine L. , Pacioni Natalia L. 
Published: March 2012

AbstractPhotochemical methods for free radical generation can provide a powerful tool to design new strategies for the synthesis of metal nanostructures. In particular, the Norrish type I cleavage of substituted benzoins can be employed as a source of strongly reducing radicals, described here as “caged electrons.” A key to an efficient nanostructure synthesis relies on the prevention of excited state quenching by the transition metal ions used as metal precursors; the paradigm presented here emphasizes the spatial‐temporal strategies that can ensure the survival of excited states so that they can perform as efficient sources of caged electrons.
Silanes as Reducing Reagents in Radical Chemistry
Authors: Chatgilialoglu Chryssostomos , Timokhin Vitaliy I. 
Published: March 2012

AbstractThis article focuses on the recent advances in organic synthesis based on the role of silyl radicals. The numerous examples of the successful use of organosilanes, and in particular tris(trimethylsilyl)silane, as radical‐based reducing agents show the flexibility and applicability of these compounds in two classes of transformations: radical reductions and consecutive radical reactions. The use of organosilanes allows reactions to be carried out under mild conditions, in different solvents including water, with excellent yields of products and remarkable chemo‐, regio‐, and stereoselectivity. The future perspectives of silyl radicals in a broad range of new synthetic applications are also given.
Biological Chemistry of Reactive Oxygen Species
Authors: Winterbourn Christine C. 
Published: March 2012

AbstractLiving organisms are continually exposed to free radicals and other reactive oxygen species as a result of metabolizing oxygen and other redox‐active compounds. Excessive production can result in biological damage, whereas in other situation, specific oxidants are generated as a host defense mechanism or as a cell signal that activates gene expression and metabolic responses. This article provides an overview of the specific reactive oxygen species that are generated biologically, how and where they arise, and their chemical reactivity with biological molecules.
Kinetics of Polymerizations
Authors: Buback Michael , Russell Gregory T. 
Published: March 2012

Abstract
First of all, the machinery for treating radical polymerization (RP) kinetics is presented. On the one hand, this involves kinetic descriptions that may be implemented without undue difficulty and that account for subtle but pivotal phenomena such as chain‐length‐dependent termination and penultimate‐unit effects in copolymerization. At the same time, this machinery also includes reliable, probing experimental methods for measuring rate coefficients. It is then shown how these tools have been used to develop mechanistic understanding of the fundamental RP reactions, which are initiation, propagation, termination, and chain transfer. In the case of propagation, there is a particular emphasis on entropic effects arising from hindered rotations, while with termination the composite model for chain‐length dependence is stressed, as is variation of overall termination rate coefficient with conversion. Finally, it is shown that chain transfer to polymer and β‐scission are recurring and important motifs in many RP systems. All in all, a pleasing picture of a scientifically maturing field is revealed as taking shape.