Initial Examples

Many easily oxidized organic sulfides exist, but, of these, tetrathiafulvalene [2] (TTF) has been more extensively researched than most, because of interest in the electrical properties of its salts. Its oxidation potential makes it a reasonable electron donor [3]. Arenediazonium salts were chosen as the partner reagents since their electron-accepting properties had been well explored [4, 5]. Furthermore, reaction of TTF with diazonium salts had recently been discussed in the Russian literature [6], but this reported only the formation of the radical-cation, TTF+. We were keen 

The loss of TTF in situ from 2b and 2c means that the radical-polar proposal had been realized TTF has since been shown to behave catalytically, but its turnover number is very limited, and it appears that it is slowly destroyed in side-reactions. 

Nucleophiles other than water can participate in the termination step. Thus methanol affords methyl ethers 3, X = OMe, and acetonitrile affords nitrilium salts which are hydrolyzed to the corresponding amides 3, X = NHAc. The nitrilium salts can also be trapped in cycloaddition reactions [8]. 

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Ring closure of more highly substituted cyclohexadienes also follows the Woodward-Hoffmarm rules and, indeed, provided the initial examples of the dichotomy between thermal and photochemical processes that led to development of the concepts underlying the Woodward-Hofimann rules. ... 

As an initial example for demonstration of the use of theoretical and empirically derived equations, a problem similar to the one in Chapter 8 on blast is posed. A... 

Separately, Paal and Knorr described the initial examples of condensation reactions between 1,4-diketones and primary amines, which became known as the Paal-Knorr pyrrole synthesis. Paal also developed a furan synthesis in related studies. The central theme of these reactions involves cyclizations of 1,4-diketones, either in the presence of a primary amine (Paal-Knorr pyrrole synthesis), in the presence of a sulfur(II) source (Paal thiophene synthesis), or by dehydration of the diketone itself (Paal furan synthesis). 

West and colleagues206 have reported the initial examples involving a N -> O/S -> O mixed donor ligand such as 2-(ethylsulphinyl)pyridine A-oxide for transition metal ion and lanthanide metal ion as shown in Scheme 22. Crystal field parameters based on... 

Historically, the oral route of administration has been used the most for both conventional and novel drug-delivery systems. There are many obvious reasons for this, not the least of which would include acceptance by the patient and ease of administration. The types of sustained- and controlled-release systems employed for oral administration include virtually every currently known theoretical mechanism for such application. This is because there is more flexibility in dosage design, since constraints, such as sterility and potential damage at the site of administration, axe minimized. Because of this, it is convenient to discuss the different types of dosage forms by using those developed for oral administration as initial examples. 

In MW-assisted chemistry reduction reactions were the last to appear on the scene the use of ammonium formate and catalytic transfer hydrogenation were initial examples [23 b]. 

Deflagration tests run under ambient pressure are relatively rudimentary. They provide information concerning only the propagation rate of deflagration after forced initiation. Examples of these tests are the UN deflagration test [143], dedicated to classification of organic peroxides, and the UN trough test [145], dedicated to classification of fertilizers. 

As an initial example let us consider the chemical reduction of cytochrome c (FW =12 400), a protein which plays a series of important roles in living organisms. The structural effects of the Fe(III)/Fe(II) redox process are known from crystallographic data, Figure 2.7a,b,c... 

The initial example utilized petroleum oil to lubricate, while the later employed Vaseline. Both lubricants served a dual function as a fuel. In the end, the sensitivity of the chlorate mixtures could only be reduced to a certain extent. Eventually, safer and more reliable explosives pushed the chlorate variants out of vogue. 

The Mukaiyama Reaction. The Mukaiyama reaction refers to Lewis acid-catalyzed aldol addition reactions of enol derivatives. The initial examples involved silyl enol ethers.40 Silyl enol ethers do not react with aldehydes because the silyl enol ether is not a strong enough nucleophile. However, Lewis acids do cause reaction to occur by activating the ketone. The simplest mechanistic formulation of the Lewis acid catalysis is that complexation occurs at the carbonyl oxygen, activating the carbonyl group to nucleophilic attack. 

We now need to define a collection of atoms that can be used in a DFT calculation to represent a simple cubic material. Said more precisely, we need to specify a set of atoms so that when this set is repeated in every direction, it creates the full three-dimensional crystal stmcture. Although it is not really necessary for our initial example, it is useful to split this task into two parts. First, we define a volume that fills space when repeated in all directions. For the simple cubic metal, the obvious choice for this volume is a cube of side length a with a corner at (0,0,0) and edges pointing along the x, y, and z coordinates in three-dimensional space. Second, we define the position(s) of the atom(s) that are included in this volume. With the cubic volume we just chose, the volume will contain just one atom and we could locate it at (0,0,0). Together, these two choices have completely defined the crystal structure of an element with the simple cubic structure. The vectors that define the cell volume and the atom positions within the cell are collectively referred to as the supercell, and the definition of a supercell is the most basic input into a DFT calculation. 

If we were only interested in bulk copper and its oxides, we would not need to resort to DFT calculations. The relative stabilities of bulk metals and their oxides are extremely important in many applications of metallurgy, so it is not surprising that this information has been extensively characterized and tabulated. This information (and similar information for metal sulfides) is tabulated in so-called Ellingham diagrams, which are available from many sources. We have chosen these materials as an initial example because it is likely that you already have some physical intuition about the situation. The main point of this chapter is that DFT calculations can be used to describe the kinds of phase stability that are relevant to the physical questions posed above. In Section 7.1 we will discuss how to do this for bulk oxides. In Section 7.2 we will examine some examples where DFT can give phase stability information that is also technologically relevant but that is much more difficult to establish experimentally. 

As an initial example of using DFT calculations to describe phase stability, we will continue our discussion of bulk metal oxides. In this chapter, we are interested in describing the thermodynamic stability of a metal, M, in equilibrium with gas-phase O2 at a specified pressure, Po2, and temperature, T. We will assume that we know a series of candidate crystal structures for the metal... 

Recent developments of novel explosive materials have concentrated on reducing the sensitivity of the explosive materials to accidental initiation by shock, impact and thermal effects. The explosive materials, which have this reduced sensitivity, are call Insensitive Munitions, (IM). Although these explosive materials are insensitive to accidental initiation they still perform very well when suitably initiated. Examples of some explosive molecules under development are presented in Table 1.5. A summary of the significant discoveries in the history of explosives throughout the world is presented in Table 1.6. 

One of the most spectacular and useful template reactions is the Curtis reaction , in which a new chelate ring is formed as the result of an aldol condensation between a methylene ketone or inline and an imine salt. The initial example of this reaction was the formation of a macrocyclic nickel(II) complex from tris(l,2-diaminoethane)nickel(II) perchlorate and acetone (equation 53).182 The reaction has been developed by Curtis and numerous other workers and has been reviewed.183 In mechanistic terms there is some circumstantial evidence to suggest that the nucleophile is an uncoordinated aoetonyl carbanion which adds to a coordinated imine to yield a coordinated amino ketone (equation 54). If such a mechanism operates then the template effect is largely, if not wholly, thermodynamic in nature, as described for imine formation. Such a view is supported by the fact that the free macrocycle salts can be produced by acid catalysis alone. However, this fact does not... 

Front The proof consists of building the following initial example with 140 vertices and symmetry Did -... 

In order to get a proof for other values of b, we need an initial example. The graph GC2,i(7etrahedron) can be interpreted in the following way. The triangular faces can be shrunken to just one point. The obtained graph is Dodecahedron with a set S of four special vertices, corresponding to those faces. For any 1 < t < 5, there exist a set S, of At vertices of Dodecahedron, such that every face is incident to t vertices of this set ... 

The initial example of a photochemical cross [2+2] cycloaddition reaction of a stilbene was the reaction of t-1 and 2,3-dimethyl-2-butene to yield the cyclobutane AO reported in... 

A new potential area for exploitation of SHG is pure organic glass-forming materials. A preliminary report of the first example in this class has recently appeared from IBM laboratories. (32) Two initial examples were given. 

The most recent method developed for the nA —> An approach relies on dynamic covalent bond formation using a metathesis reaction. In this case, reactions are typically under thermodynamic control, providing the potential for increased selectivity in product formation. The initial examples using alkyne metathesis toward the formation of SPMs were reported by Adams, Bunz, and coworkers using the precatalyst [Mo(CO)6] [27,28], but rather low yields of the desired products (4) limited general applicability (Scheme 6.2). Recent efforts by Moore and coworkers using a Mo(VI)-alkylidyne catalyst, however, have refined this process such that precipitation-driven reactions now provide moderate to excellent results (see Scheme 6.24) [29]. 

Before we begin considering shifts in an equilibrium system, we need a quantitative way to describe the state of the system at any time, whether it has established equilibrium or not. In Chapter 13, you learned about the reaction quotient, Q, which was used to describe equilibrium systems. In solubility equilibria, we re not really dealing with a quotient—-just a product. Because the expression is the product of the concentrations of two different ions, the equilibrium expression that describes solubility equilibria is known as the ion product. Q is calculated in the same way as K, except it does not necessarily describe a system at equilibrium. Referring to our initial example, for the equilibrium shown below... 

In the initial example in this chapter, the stoichiometric relationship between all reactants and products was one-to-one. For every mole of reactant used, a mole of product was produced. From your work in previous chapters, you know that many reactions do not follow this simple pattern (it sure would make balancing equations easier if they did, though ). How do you set up an expression for a reaction where the stoichiometric relationships are not one-to-one If we refer to the general reaction shown below... 

This equation shows that the sodium ion is a spectator ion, and does not react. Since there is 2 mol of sodium ion present initially (Example 9.10), and the sodium does not react, there will always be 2 mol of sodium ion present no matter how much barium nitrate is added. ... 

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