Chemistry, unique characteristics

Chemistry. The material and energy available in plasmas can be used to excite materials and drive chemical reactions. The unique characteristics of plasmas, especially thek abundance of energetic species, have been exploited in plasma chemical apphcations (79—84). 

The stability of suspensions, emulsions, creams, and ointments is dealt with in other chapters. The unique characteristics of solid-state decomposition processes have been described in reviews by D. C. Monkhouse [79,80] and in the monograph on drug stability by J. T. Carstensen [81]. Baitalow et al. have applied an unconventional approach to the kinetic analysis of solid-state reactions [82], The recently published monograph on solid-state chemistry of drugs also treats this topic in great detail [83],... 

It might be expected that the aromatic character of (14) would lend unique characteristics to its chemistry. Studies of the olefin addition and C—H insertion reactions of the carbene, however, indicate that it is poorly stabilized and highly reactive.<26)... 

Palladium chemistry involving heterocycles has its unique characteristics stemming from the heterocycles inherently different structural and electronic properties in comparison to the corresponding carbocyclic aryl compounds. One example illustrating the striking difference in reactivity between a heteroarene and a carbocyclic arene is the heteroaryl Heck reaction (vide infra, see Section 1.4). We define a heteroaryl Heck reaction as an intermolecular or an intramolecular Heck reaction occurring onto a heteroaryl recipient. Intermolecular Heck reactions of carbocyclic arenes as the recipients are rare [12a-d], whereas heterocycles including thiophenes, furans, thiazoles, oxazoles, imidazoles, pyrroles and indoles, etc. are excellent substrates. For instance, the heteroaryl Heck reaction of 2-chloro-3,6-diethylpyrazine (1) and benzoxazole occurred at the C(2) position of benzoxazole to elaborate pyrazinylbenzoxazole 2 [12e]. 

Palladium chemistry of heterocycles has its idiosyncrasies stemming from their different structural properties from the corresponding carbocyclic aryl compounds. Even activated chloroheterocycles are sufficiently reactive to undergo Pd-catalyzed reactions. As a consequence of a and y activation of heteroaryl halides, Pd-catalyzed chemistry may take place regioselectively at the activated positions, a phenomenon rarely seen in carbocyclic aryl halides. In addition, another salient peculiarity in palladium chemistry of heterocycles is the so-called heteroaryl Heck reaction . For instance, while intermolecular palladium-catalyzed arylations of carbocyclic arenes are rare, palladium-catalyzed arylations of azoles and many other heterocycles readily take place. Therefore, the principal aim of this book is to highlight important palladium-mediated reactions of heterocycles with emphasis on the unique characteristics of individual heterocycles. 

Sulfur has four unique characteristics related to its occurrence and chemistry in soil. As sulfate, it is one of the principle counterions that keep the soil electrically neutral. Soil receives constant additions of sulfur through volcanic activity around the world and industrial pollution, usually in the form of acid rain. This means that soils usually have sufficient sulfur for plant growth. Lastly, plants can take and use sulfur dioxide from the air as a source of sulfur for growth [22,38],... 

Chemistry - as a scientific and technological discipline - has some unique characteristics. In contrast to physics, where most of the underlying laws can be given in explicit and sometimes simple mathematical form, many of the laws governing chemical phenomena are either not explicitly known, or else have a mathematical form that still eludes an exact solution. Still, chemistry does provide - and rests on- quantitative data of physical or chemical properties of high numerical precision. A search for quantitative relationships is thus suggested, despite the lack of a tractable theoretical basis. 

Several bismuth compounds that can be used in aqueous media have been introduced. Due to increasing demand of water as a solvent in organic synthesis, catalysts that can be used in aqueous media are becoming more and more important. Although bismuth Lewis acids are not very stable in water, it has been shown that they can be stabilized by basic ligands. Chiral amine and related basic ligands combined with bismuth Lewis acids are particularly useful in asymmetric catalysis in aqueous media. On the other hand, Bi(OH)3 is stable in water and works as an efficient catalyst in water. Because of the unique characteristics of bismuth compounds, other chiral and achiral bismuth catalysts will be focused on and developed rapidly in the field of synthetic organic chemistry. 

Although this area of reactions at interfaces is relatively new and not well understood, it may potentially be more significant than previously recognized. Because of the unique characteristics of such processes both kinetically and mechanistically compared to bulk aqueous-phase or gas-phase reactions, we suggest the term fourth phase be used to describe this chemistry at gas-liquid interfaces in the atmosphere. 

Palladium chemistry has rapidly become an indispensable tool for synthetic organic chemists. Palladium-catalyzed coupling is now the method of choice for the synthesis of a wide range of biaryls and heterobiaryls. The number of applications of palladium chemistry to the syntheses of heterocycles has grown exponentially. In this book important palladium-mediated reactions involving heterocycles are highlighted with emphasis on the unique characteristics of individual heterocycles. 

VINYL ESTER RESINS. The vinyl ester resins are a relatively recent addition1 to thermosetting-polymer-chemistry. Superficially, they are similar to unsaturated polyester resins insofar as they contain ethylmic lmsaturation and are cured throngh a free-radical mechanism, usually in the presence of a vinyl monomer, such as styrene. However, close examination of the chemistry and structure of the vinyl ester resins demonstrates several basic differences which lead to their unique characteristics. 

Although the first result is in line with those obtained for MgO-NiO, MgO-CoO, and ZnO-CoO solid solution, the second suggests that the chemistry of silica-supported ions has some unique characteristics that merit further consideration. The ability to form multicarbonyl species suggests a state of coordinative unsaturation higher than that observed for the same or similar ions in solid solutions and represents a strong indication that high... 

The chemistry of the carbon-carbon triple bond is similar to that of the double bond. In this chapter, we see that alkynes undergo most of the same reactions as alkenes, especially the additions and the oxidations. We also consider reactions that are specific to alkynes some that depend on the unique characteristics of the C=C triple bond, and others that depend on the unusual acidity of the acetylenic =C—H bond. 

Several types of the early Solar System materials are available for laboratory analysis (see Chapter 1 and Table 1.1 and Fig. 1.1). Each material has unique characteristics and provides specific constraints on the chemistry of the solar nebula. Major components of this sample are meteorites, fragments of asteroids, that serve as an excellent archive of the early Solar System conditions. Primitive chondritic meteorites contain glassy spherical inclusions termed chondrules, some of the oldest solids in the Solar System. Most chondrites were modified by aqueous alteration or metamorphic processes in parent bodies but there are some chondrites that are minimally altered (un-equilibrated chondrites, UCs). They have yielded a wealth of information on the chemistry, physics, and evolution of the young Solar System. 

When the valence-band hole and the conduction-band electron are both trapped by an appropriate oxidation or reduction half reaction, singly oxidized and reduced species are formed on the surface of the photocatalyst. Because these adsorbed intermediates can move about the surface, either migrating closer together or diffusing away from each other, before back-electron transfer occurs, novel chemistry is likely to ensue. It is a unique characteristic of photoelectrochemical catalysts that both oxidized and reduced species are produced on the same surface. As a result,... 

Each preservative has unique characteristics that might affect its suitability for a particular application. These include factors such as appearance, odour, toxicity, wood species compatibility and availability. The discussion that follows provides a basic background to a wide range of preservative systems. Some of these systems are still in use today, while others have been phased out and others are currently under development. Further discussion of preservative systems can be found elsewhere (Ibach, 1999 Nicholas, 1973b Richardson, 1993 Schultz and Nicholas, 2003). It will be readily apparent from this section that the transition away from traditional heavy metal broad spectrum biocidal compounds to organic chemistries has added significant complication to the wood preserving industry as a whole. 

Isocyanides have attracted much attention in synthetic organic chemistry, and have led to the development of a variety of useful synthetic transformations [1]. In particular, carbon-carbon bond forming reactions using isocyanides as key reagents have been extensively studied during the past 50 years, as they allow the realization of useful multi-component assembly reactions, such as the Ugi and Passerini reactions [2]. These have once again been highlighted in recent years with the development of combinatorial chemistry. The characteristic reactions of isocyanides are mostly ascribed to the unique reactivity of the isocyano carbon atom, which can be represented by a divalent, carbene-like electronic structure (Scheme 1). In this respect,... 

Palladium chemistry involving heterocycles has many unique characteristics stemming from the inherently different structural and electronic properties of heterocyclic molecules in comparison to the corresponding aromatic carbocycles. One salient feature of heterocycles is the marked activation at positions a and y to the heteroatom. For N-containing heterocycles, the presence of the N-atom polarizes the aromatic ring, thereby activating the ex and y positions, making them more prone to nucleophilic attack. For example, the order of S Ar displacement of heteroaryl hahdes with EtO is [3] ... 

Tlie complicated part of organic chemistry arises from the unique characteristics of carbon s preferred number of bonds (four). Other atoms can take on four or even more than four bonds, but carbon s small size compared to other members of its atomic group cause its properties and molecular behavior to be largely unique. 

Due to practical significance and theoretical interest, much effort has been made to clarify the unique characteristics of metal ion/polyelectrolyte mixture solutions in various disciplines of chemistry. Since a proper equilibrium expression for metal ion binding to polymer molecules is indispensable for the quantification of the physicochemical properties, apparent or macroscopic equilibrium constants have been determined. Unfortunately, however, these overall constants are usually defined arbitrarily, being dependent on the research groups, the experimental techniques, and the systems to be investigated hence they are not comparable with each other nor re-latable to the intrinsic equilibrium constants defined at respective reaction sites. Compared with the situation for the equilibrium analyses of metal complexation with monomer ligands, to which the law of mass action can directly be applied, complete analytical treatment of the metal ion/ polyelectrolyte complexation equilibria has not yet been established even at the present time. There are essential difficulties inherent in the analyses of metal complexation equilibria in polyelectrolyte solutions. 

It is stated that nasal sprays have unique characteristics with respect to formulation, container closure system, manufacturing, in-process and final controls and stability. The product must deliver reproducible doses during the whole life of the product. Excipient controls are discussed in the FDA draft guidance in many respects, the chemistry, manufacturing and controls (CMC) standards expected of excipients are starting to approach those required of the active pharmaceutical ingredient (API). 

While the lanthanides (strictly defined as the 14 elements following lanthanum in the periodic table, but as normally used also include lanthanum itself) have several unique characteristics compared to other elements, their appearance in the history of the development of organometallic chemistry is rather recent. Since the f orbitals are filled gradually from lanthanum ([Xe]4f°) to lutetium ([Xe]4f14), they are regarded as the f-block elements, which are discriminated from the d-block transition elements. 

Subsurface physical, chemical and biological conditions are quite variable in space and time. These factors can be the source of considerable "natural" variability in ground-water chemistry at both clean and contaminated sites. Sampling and analytical errors or variability can be controlled if these activities are planned and documented as protocols which take into account the unique characteristics of individual sampling points and conditions. It is critical that a sound hydrogeologic basis exists for the steps in the sampling protocol which precede actual sample collection. 

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