Alkane elimination reactions processes

Alkane activation by metal atoms by osmium atoms, 273-274 by rhenium atoms, 265-271 by tungsten atoms, 270-272 description, 265 Alkane elimination reactions, processes, 20,22... 

In contrast to the results obtained for dehydrogenation reactions, kinetic energy release distributions for alkane elimination processes can usually be fit with phase space theory. Results for the loss of methane from reaction 9 of Co + with isobutane are shown in Figure 10b. In fitting the... 

The uncertainty about the formation mechanism is eliminated when such method is used for the determination of the G(5 i) value, which is invariant to the formation route. Such method is the comparison of the yields of those products, which are formed only in one way in the reaction of the Si molecules. Such products come from the singlet decay channel fluorescence photons, products of H2 or alkane elimination. The triplet channel due to the large triplet yield originating from other processes than the Si Tn ISC (e.g., direct triplet excitation, or charge recombination with triplet product) cannot be used for the calculation of the Si yield. The calculations are based on the equation ... 

The vertical electron affinity (EA) of acetone is given as —1.51 eV by Jordan and Burrow386. Lifshitz, Wu and Tiernan387 determine—among other compounds—the excitation function and rate constants of the slow proton transfer reactions between acclone-Ih, acetone-Dg and other ketones. The acetone enolate anion has been produced in a CO2 laser induced alkane elimination from alkoxide anions by Brauman and collaborators388-390. These show, e.g. that the methane elimination from t-butoxide anion is a stepwise process ... 

Preparation. The synthesis of alkylzinc alkoxides and aryloxides is achieved by an alkane elimination process in the simple reaction of a dialkylzinc compound, R2Zn, with one equivalent of an alcohol, R OH (equation 18). This reaction proceeds either in hydrocarbon solvents or neat solution, to give essentially quantitative yields of the desired products. The volatility of the RH side product helps to drive the equilibrium to the right. The formation of relatively strong Zn-O and C-H bonds, at the expense of breaking the O-H and a relatively weak Zn-C bond also guarantee favorable reaction energetics. 

The title compounds are usually obtain in a straightforward manner and in almost quantitative yields by alkane elimination process between a dialkylzinc compound ZnRs and the desired thiol R SH or selenol R SeH species (equation 18). This reaction works equally well in hydrocarbon solvent or neat solution. If thiocyanogen (SCN)2 is used as the reagent, then alkylzinc thiocyanate derivatives (RZnSCN) are obtained. ... 

Elimination reactions One way to change an alkane into a chemically reactive substance is to form a second covalent bond between two carbon atoms, producing an alkene. The main industrial source of alkenes is the cracking of petroleum. The process of cracking, shown in Figure 23-17, breaks large alkanes into smaller alkanes, alkenes, and aromatic compounds. Why do you suppose the term cracking was applied to this process ... 

Depending on the internal energy and the substituents attached to the pentacoordinate silicon adduct anions, not only exchange processes, like reaction 146, or substitutions (reactions 143-145) occur, but alkane elimination is also frequently observed, in particular under ICR conditions. Alkane elimination is favoured if the adduct does not contain a good leaving group (allyl, alkoxide). Three instructive examples are described in reactions 147-149164b. 

EIEs provide invaluable information concerning both molecular structure and the determination of reaction mechanisms. EIEs are traditionally defined as the ratio of equilibrium constants for unlabeled and labeled reactants and products (EIE = A h/A d Figure 2). For oxidative addition and reductive elimination reactions, the presence of intermediates along the reaction coordinate, such as alkane cr-complexes and agostic interactions, make these reactions multistep processes and hence, additional terms are necessary in order to more fully describe the overall mechanism. Thus, reductive elimination may consist of a reductive coupling (rc) step followed by dissociation (d), whereas the microscopic reverse, oxidative addition, could consist of ligand association (a) followed by oxidative cleavage (oc), as illustrated in Scheme 6. 

In previous chapters we discussed the ways reagents attack organic substrates (e.g., nucleophilic substitution, addition reactions and elimination reactions). Let us examine some interesting ways that C—C bonds can be broken in a homolytic manner which, in turn, lead to unusual predictions concerning reaction paths or intermediate structures. We start this discussion with a simple example of homolytic C—C bond cleavage in an alkane. A correlation diagram for this process is displayed in 11.51. 

Most reductive elimination reactions are induced thermally, but some important reductive elimination reactions are induced photochemically. Most examples of such reductive eliminations form dihydrogen from metal-dihydride complexes. Two examples of the photochemical reductive elimination of dihydrogen to generate intermediates that add alkanes are shown in Equations 8.6 and 8.7. In these examples, the photochemical irradiation provides the energy to induce the reductive elimination process. 

A more general reaction between kojic acid and aldehydes is a trimolecu-lar condensation discovered by Barham and Reed." By a process of elimination, they arrived at the conclusion that C6 of kojic acid was most probably the point of attack two molecules of kojic acid reacted with one molecule of the aldehyde, with the elimination of one molecule of water, giving a product of structure LXXV. Such compounds were prepared from kojic acid and the following aldehydes the normal alkanals from formaldehyde to heptanal, benzaldehyde, cinnamaldehyde, hydrocinnamaldehyde, 2-furaldehyde, and acrolein. The compound derived from kojic acid and benzaldehyde (LXXV, R = phenyl) was also obtained by treating LXXII (R = phenyl) with hot, aqueous sodium carbonate.92... 

Sigma-bond metathesis at hypovalent metal centers Thermodynamically, reaction of H2 with a metal-carbon bond to produce new C—H and M—H bonds is a favorable process. If the metal has a lone pair available, a viable reaction pathway is initial oxidative addition of H2 to form a metal alkyl dihydride, followed by stepwise reductive elimination (the microscopic reverse of oxidative addition) of alkane. On the other hand, hypovalent complexes lack the... 

There is ample evidence that the reductive elimination of alkanes (and the reverse) is a not single-step process, but involves a o-alkane complex as the intermediate. Thus, looking at the kinetics, reductive elimination and oxidative addition do not correspond to the elementary steps. These terms were introduced at a point in time when o-alkane complexes were unknown, and therefore new terms have been introduced by Jones to describe the mechanism and the kinetics of the reaction [5], The reaction of the o-alkane complex to the hydride-alkyl metal complex is called reductive cleavage and its reverse is called oxidative coupling. The second part of the scheme involves the association of alkane and metal and the dissociation of the o-alkane complex to unsaturated metal and free alkane. The intermediacy of o-alkane complexes can be seen for instance from the intramolecular exchange of isotopes in D-M-CH3 to the more stable H-M-CH2D prior to loss of CH3D. 

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