Direct and indirect electrochemical generation of alkoxycarbenium ion pools from thioacetals

Thioacetals were found to be effective precursors to generate and accumulate alkoxycarbenium ions based on direct and indirect cation pool methods. Alkoxycarbenium ions thus generated reacted with carbon nucleophiles such as allylsilanes and enol silyl ethers to give C-C bond formation products in good yields.     

Indirect cation pool method. Rapid generation of alkoxycarbenium ion pools from thioacetals

A sequential one-pot indirect cation pool method has been developed. The method involves the electrochemical generation and accumulation of ArS(ArSSAr)+ at low temperature (step 1) and the follow-up reaction with a thioacetal to generate an alkoxycarbenium ion pool (step 2), which reacts with various carbon nucleophiles (step 3). Steps 2 and 3 are extremely fast. The electrogenerated ArS(ArSSAr)+ was well-characterized by 1H NMR and CSI-MS. The alkoxycarbenium ion pool generated by the present indirect method exhibited 1H and 13C NMR spectra and thermal stability similar to those of the alkoxycarbenium ion pool generated by the direct electrochemical method.     

Intramolecular participation in alkoxycarbenium ion pools

[reaction: see text] Alkoxycarbenium ions having no substituents on the cationic carbon have been accumulated as "cation pools" by the introduction of an ether group in an appropriate position. Intramolecular participation of the ether oxygen is suggested to be responsible for stabilization of the alkoxycarbenium ions.     

Graphene quantum dots from chemistry to applications

Graphene quantum dots (GQDs) have been widely studied in recent years due to its unique structure-related properties, such as optical, electrical and optoelectrical properties. GQDs are considered new kind of quantum dots (QDs), as they are chemically and physically stable because of its intrinsic inert carbon property. Furthermore, GQDs are environmentally friendly due to its non-toxic and biologically inert properties, which have attracted worldwide interests from academic and industry. In this review, a number of GQDs preparation methods, such as hydrothermal method, microwave-assisted hydrothermal method, soft-template method, liquid exfoliation method, metal-catalyzed method and electron beam lithography method etc., are summarized. Their structural, morphological, chemical composition, optical, electrical and optoelectrical properties have been characterized and studied. A variety of elemental dopant, such as nitrogen, sulphur, chlorine, fluorine and potassium etc., have been doped into GQDs to diversify the functions of the material. The control of its size and shape has been realized by means of preparation parameters, such as synthesis temperature, growth time, source concentration and catalyst etc. As far as energy level engineering is concerned, the elemental doping has shown an introduction of energy level in GQDs which may tune the optical, electrical and optoelectrical properties of the GQDs. The applications of GQDs in biological imaging, optoelectrical detectors, solar cells, light emitting diodes, fluorescent agent, photocatalysis, and lithium ion battery are described. GQD composites, having optimized contents and properties, are also discussed to extend the applications of GQDs. Basic physical and chemical parameters of GQDs are summarized by tables in this review, which will provide readers useful information.     

Statistical rate theory and kinetic energy-resolved ion chemistry: theory and applications

Ion chemistry, first discovered 100 years ago, has profitably been coupled with statistical rate theories, developed about 80 years ago and refined since. In this overview, the application of statistical rate theory to the analysis of kinetic-energy-dependent collision-induced dissociation (CID) reactions is reviewed. This procedure accounts for and quantifies the kinetic shifts that are observed as systems increase in size. The statistical approach developed allows straightforward extension to systems undergoing competitive or sequential dissociations. Such methods can also be applied to the reverse of the CID process, association reactions, as well as to quantitative analysis of ligand exchange processes. Examples of each of these types of reactions are provided and the literature surveyed for successful applications of this statistical approach to provide quantitative thermochemical information. Such applications include metal-ligand complexes, metal clusters, proton-bound complexes, organic intermediates, biological systems, saturated organometallic complexes, and hydrated and solvated species.     

Transformation of thioacetals to cyclopropanes

Cyclopropanes were obtained by the titanocene(II)-promoted reaction of thioacetals with vinyl pivalate. It was also found that vinycyclopropanes were produced by a similar treatment of thioacetals with the titanocene(II) species in the presence of 1,3-dienes.     

Oxidative generation of diarylcarbenium ion pools

"Cation pools" of diarylcarbenium ions have been generated by the oxidative C-H bond dissociation of diarylmethanes using anodic oxidation. "Diarylcarbenium ion pools" thus generated react with various nucleophiles, such as allylsilanes, ketene silyl acetals, and aromatic compounds. The reductive homocoupling of the "diarylcarbenium ion pool" has been achieved. The dimer thus obtained also serves as a precursor of the "diarylcarbenium ion pool" via oxidative C-C bond dissociation. [reaction: see text]     

Ruthenium polypyridyl chemistry; from basic research to applications and back again

Since the mid 1970's interest in the chemistry and applications of ruthenium polypyridyl complexes has increased steadily. In this perspective, the development of this area is tracked and discussed taking into account new scientific developments as well as novel applications. The interaction between basic and applied research is of particular importance and selected examples are highlighted.     

Solution chemistry and secondary ion emission from amine-glycerol solutions

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Secondary ion mass spectra were obtained from a series of C₄-C₁₀ n-alkylamines introduced via the gas phase onto glycerol. It was found that the amine-characteristic secondary ion intensity varied linearly with amine partial pressure. Henry's law constants and surface activity constants for each of the amines in glycerol solution were measured. A linear correlation was found between amine-characteristic secondary ion intensity and Henry's law concentrations. The concentrations calculated from Henry's law were too low to yield the intensities observed, indicating that secondary ion precursors were not free-base amine molecules but ions in solution. Explicit kinetic equations describing glycerol and amine protonation and deprotonation as a result of primary ion damage to the solutions are derived to rationalize the observed spectra.     

Electrochemical synthesis of dendritic diarylcarbenium ion pools

Dendritic diarylcarbenium ion pools were synthesized by the low temperature electrochemical oxidation of the corresponding dendritic (diarylmethyl)trimethylsilanes, which were prepared by use of the iterative method consisting of electrochemical activation and Friedel-Crafts type coupling. Time-course NMR studies revealed that thermal stability of dendritic diarylcarbenium ions depends both on the generation of the dendritic structure and on the para-substituents of the terminal phenyl groups. Dendritic diarylcarbenium ions up to the third generation exhibited high reactivity as a carbon electrophile.     

Theoretical chemistry: current applications to photochemistry and thermochemistry

A historical perspective is given contrasting challenges and advances in theoretical chemistry at the time the first issue of Theoretical Chemistry Accounts appeared in 1962 and the progress achieved since then as expressed in current state-of-the-art applications in photochemistry and thermochemistry.     

Going to extremes: "super" armed glycosyl donors in glycosylation chemistry

This concept article gives an overview of stereoelectronic effects in monosaccharide systems and how these can be used to dramatically enhance the reactivity of glycosyl donors in oligosaccharide synthesis.     

Photoelectron spectra and ion chemistry of imidazolide

The 351.1 nm photoelectron spectrum of imidazolide anion has been measured. The electron affinity (EA) of the imidazolyl radical is determined to be 2.613 +/- 0.006 eV. Vibrational frequencies of 955 +/- 15 and 1365 +/- 20 cm(-1) are observed in the spectrum of the (2)B1 ground state of the imidazolyl radical. The main features in the spectrum are well-reproduced by Franck-Condon simulation based on the optimized geometries and the normal modes obtained at the B3LYP/6-311++G(d,p) level of density functional theory. The two vibrational frequencies are assigned to totally symmetric modes with C-C and N-C stretching motions. Overtone peaks of an in-plane nontotally symmetric mode are observed in the spectrum and attributed to Fermi resonance. Also observed is the photoelectron spectrum of the anion formed by deprotonation of imidazole at the C5 position. The EA of the corresponding radical, 5-imidazolyl, is 1.992 +/- 0.010 eV. The gas phase acidity of imidazole has been determined using a flowing afterglow-selected ion tube; delta(acid)G298 = 342.6 +/- 0.4 and delta(acid)H298 = 349.7 +/- 0.5 kcal mol(-1). From the EA of imidazolyl radical and gas phase acidity of imidazole, the bond dissociation energy for the N-H bond in imidazole is determined to be 95.1 +/- 0.5 kcal mol(-1). These thermodynamic parameters for imidazole and imidazolyl radical are compared with those for pyrrole and pyrrolyl radical, and the effects of the additional N atom in the five-membered ring are discussed.     

Some applications of thermal analysis to the coordination chemistry

The behaviour of complexes of the type MeD2I2 (Me=Co,D = acetylacetone or benzoylacetone,I = imidazole and derivatives in the course of the stepwise thermal degradation is different. In the case ofD = acetylacetone in the first step acetylacetone is split off. At D = benzoylacetone the decomposition starts with the partial elimination of the heterocyclic ligands.In-position unsubstituted nickelacyclic complexes from type (bipy)Ni(CH₂CH₂CH₂COO) decompose by a reductive elimination and separating of CO₂ forming a (bipy)Ni-intermediate. A single reductive decoupling is hindered by blocking up the-position.Opposite to the high thermal stability of the trimesityl aluminium the intermediates Almes₂Cl and AlmesCl₂ show with decreasing amounts of mesityl groups and increasing content of halogene, respectively, a significant decreasing thermal stability.The thermal degradation of nickelchelates of alkylsubstituted chinolin-8-ol starts with the dehydration followed by a different separation of the ligands as a function of the chain-length and the position of the substituents of the ligands.

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Zusammenfassung Das Zersetzung Verhalten der Komplexverbindungen vom Typ C0D2I2 (P = acetylaceton, Benzoylaceton;I = Imidazol oder Derivate) erfolgt stufenweise. Im Falle vonD = Acetylaceton erfolgt zuerst eine Eliminierung von Acetylaceton wärend beiD = Benzoylaceton zuerst ein Heteroligand eine Abspaltung erfährt.Bei einer unsubstituierten-Position von Nickelacyclen des Typs (bipy)Ni(CH₂CH₂CH₂COO) erfolgt eine thermisch induzierte-Hydrideliminierung unter Ringspaltung und Freisetzung von CO₂.Im Gegensatz zur hohen thermischen Stabilität des Trimesityl Aluminium erfahren die Zwischenverbindungen Almes₂Cl und AlmesCl₂ mit abnehmenden Mesityl- bzw. zunehmenden Chlorgehalt einen wessentlich früheren thermischen Zerfall. Bei zunehmenden Kovalenzgrad ist hier ein Einfluss der veränderten Polarisation anzunehmen.Der thermische Abbau der prinzipiell wasserhaltig kristallisierenden Nickelchelate von alkylsubstituierten Chinolin-8-ol beginnt jeweils mit der Dehydratisierung. In Abhängigkeit von der Kettenlänge und der Position der Substitution am Chinolin schliesst sich der thermische Abbau der Chelatliganden ein- bzw. mehrstufig an.

     

Practical applications of radiation chemistry

The physical, chemical, and biological effects of ionizing radiation on matter are the basis of many practical applications. The number of such applications is growing, and sources of gamma radiation and X-rays are now being operated in harsh, demanding environments. They play an important role in the economic development of many countries. The text was submitted by the author in English.     

Direct dendronization of polystyrenes using dendritic diarylcarbenium ion pools

Dendritic diarylcarbenium ions exhibited sufficient electrophilicity to react with unfunctionalized polystyrenes. The polymers obtained by the reaction of the first and the second generation dendritic diarylcarbenium ions with polystyrenes were well characterized by MALDI-TOF MS and SEC-MALLS analyses and observed by AFM.     

Organoaluminum chemistry and its application to the initiation of carbenium ion polymerization

Organoaluminum compounds are weak Lewis acids, which specifically react with a number of reagents (or bases) and generate an electrophile (initiator)gegenion pair, reminiscent of classical Friedel—Crafts complexes. These complexes, under suitable reaction conditions, initiate polymerization of cationically polymerizable monomers producing useful high molecular weight polymers. In recent years a number of such organoaluminum-initiator systems have been systematically explored and their chemistry unravelled. As a consequence new insights have been gained which has led to newer applications of organoaluminum compounds in organic as well as new polymer synthesis.The present paper briefly summarizes the results in this area, especially from the point of view of initiator generation. Some recent results on the initiation of carbenium ion polymerizations using the oxyhalides of sulfur and phosphorous in conjunction with organoaluminum compounds are discussed.