Elimination reactions defined

Stereoselectivity was defined and introduced in connec tion with the formation of stereoisomeric alkenes in elimination reactions (Sec tion 5 11)... 

High reaction temperatures can cause numerical overflow problems in the computer calculation of k, owing to the very large values generated by the exponential term. This can often be eliminated by defining a value of the rate constant, kg, for some given temperature, Tq. Thus... 

Recently organosilicon compounds are being used for the synthesis of olefines by elimination reactions both in acidic and basic conditions. Thus P hydroxysilanes give defines. These reactions have been shown to be highly stereospecific. The acid catalysed elimination taking place by an anti pathway and the base induced elimination taking place by a syn pathway. 

In organic chemistry, oxidation is defined as a reaction in which a carhon atom forms more bonds to oxygen, O, or less bonds to hydrogen, H. An oxidation that involves the formation of double C = O bonds may also be classified as an elimination reaction. 

Using rate data from IR experiments on the overall elimination reaction from [Rh(C(0)Me)(C0)l3] in the absence of Mel and the equilibration of Rh( C(0) Me)(CO)l3] with [Rh(C(0)Me)( C0)l3] in neat Mel it was possible to estimate the two further rate constants that defined the system. Putting these together showed that [RhMe(CO)2l3] is unstable both with respect to reductive elimination and migratory insertion at 35 °C in MeI/CH2Cl2 [32]. 

Density functional theory and a high-level cib initio procedure (G2+) have been used to explore the potential energy surface for the base-induced elimination reaction of fluoride ion with ethyl fluoride.11 The DFT barriers are smaller and looser than those predicted by the ab initio method but the nature of the transition state cannot be defined with confidence since the predictions are unusually sensitive to the choice of functional and basis set. The results suggest that improvement in density functional methods will require fundamental change in the functionals themselves. 

Therefore, it must be concluded that earlier attempts to prove the existence of stable, well-defined alkyl cations were unsuccessful in experiments using sulfuric acid solutions and inconclusive in the interaction of alkyl halides with Lewis acid halides. Proton elimination reactions or dialkyl halonium ion formation may have affected the early conductivity studies. 

A couple of prototypical examples of the cyclic version of the Heck reaction, defined as a process consisting of alkene carbopalladation followed by -elimination, were reported during the 1984-1985 period [9,10]. Almost concurrently, seminal examples of both the non-Heck cyclic carbopallation reactions [10,30] were reported during the 1983-1985 period. Thus, with due respect paid to earlier discoveries of alkyne cyclooligomerization via cascade carbopalladation [7,8] as well as copolymerization [24] and cocyclization [25,... 

For complex chemistry, in many cases, a conserved scalar or a mixture fraction approach can be used, in which a single conserved scalar (mixture fraction) is solved instead of transport equations for individual species. The reacting system is treated using either chemical equilibrium calculations or by assuming infinitely fast reactions (mixed-is-reacted approach). The mixture fraction approach is applicable to non-premixed situations and is specifically developed to simulate turbulent diffusion flames containing one fuel and one oxidant. Such situations are illustrated in Fig. 5.6. The basis for the mixture fraction approach is that individual conservation equations for fuel and oxidant can be combined to eliminate reaction rate terms (see Toor, 1975 for more details). Such a combined equation can be simplified by defining a mixture... 

That ends this chapter on elimination reactions. It is apparent from the foregoing discussion that elimination reactions are far less well defined than either the substitution or addition reactions that we had studied previously. However, it was still possible to rationalise the production of the experimentally observed products. We will now look at sequential reactions, in which an addition reaction is followed by an elimination, or vice versa, and so leads to an overall substitution reaction... 

This is the final chapter in this part of the book. We have already come across some reactions that formally involve oxidation or reduction of the carbon atoms in the molecule, e.g. the formation of a vicinal diol from a double bond is an oxidation reaction, while the addition of a hydrogen molecule to an alkene is a reduction reaction. However, such reactions proceed by clearly defined mechanisms that could be conveniently placed into other general mechanistic divisions, e.g. addition or elimination reactions, and so they were considered under those headings. There remain, however, a number of reactions that do not comfortably fit into any of the previous reaction types that we have studied so far. 

Any way, these very simple rules help in the choice of activating agents and we are working with the aim of refining them. Moreover, we shall see later (Chapter IV. 1.2.2.) that we have started to define rules for elimination reactions. 

The term "cheletropic reaction" defines reactions in which two a bonds to a single atom are made or broken conceitedly. A widely studied example, theoretically as well as experimentally, is the cheletropic elimination of sulfur dioxide from a cyclic sulfolene to generate stereochemically pure dienes or polyenes. ... 

The general stoichiometry of the reaction is shown in Scheme 1. The equilibrium reaction defining the first step (forward = oxidative addition reverse = reductive elimination) was verified previously. Figure 1 illustrates the oxidative addition of Mel to [RhCl(CO)(Y(p-Tol)3 2]. 

Smith periodate degradation, partial acidic hydrolysis, reduction of uronosyl residues, acetolysis, as well as base elimination reactions and other degradation procedures that can be applied to uronosyl residues, and n.m.r. spectroscopy [261]. Increasing availability of purified enzymes with well-defined action patterns should assist future studies [106, 262], Structural features can also be recognised by monoclonal antibodies [268],... 

A base is defined as a species that accepts protons. In the above reaction the OH acts as a base and accepts a proton from the bromoalkane. So, in elimination reactions the OH acts as a base, whereas, as you saw in Part 2, in substitution reactions the same ion acts as a nucleophile (attacking and forming a bond to a carbon atom). Don t worry too much about the interplay between elimination and substitution reactions just now we shall discuss this topic in more detail in Section 4. Just remember that OH can act in two different ways, depending on the type of reaction. In the mechanism shown in Reaction 1.1, the base removes the proton the two electrons from the carbon-hydrogen bond form the new bond of the double bond and the carbon-bromine bond breaks heterolytically, the two electrons going to the bromine to give a bromide anion. 

We then went on to discuss elimination reactions in which Y is H. However, other 13-elimination reactions are known in which neither X nor Y is a hydrogen atom. These reactions are useful because the position of the new double bond is defined by the position of X and Y, and also because elimination usually occurs to the exclusion of substitution. Let s look at two such examples, and then go on to consider how alkynes are produced by elimination reactions. 

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