Isomerization reactions, internal

Internal isomerization reactions of butylhydroperoxy radicals formed during the oxidation of n-butane and i-butane... 

Internal isomerization reactions also play an important role during pyrolysis. In fact, 1-4, 1-5 and 1-6 H-transfer reactions are easily explained on the basis of internal H-abstraction reactions, via five-, six- and seven-membered ring intermediates. The rate constants of these isomerization reactions are estimated in terms of the number of atoms in the transition-state ring structure (including the H-atom) and the type of sites involved in the H-transfer (Benson, 1976). 

Isomerization of the ion-pair followed by internal remrn that leads to formation of a neutral isomerized reaction product. 

Olefin isomerization reactions range from some of the most facile using acid catalysts to moderately difficult and, as components of more complex reaction schemes such as catalytic cracking, may be among the most common reactions in hydrocarbon processing. As stand-alone reactions, they are primarily used to shift the equilibrium between terminal and internal olefins or the degree of branching of the olefin. While olefin isomerization was considered for the production of MTBE, today stand-alone olefin isomerization processes are only considered for a few special situations within a petrochemical complex. 

The simplest general type of chemical process to consider is an isomeric reaction in which a molecule undergoes an internal rearrangement... 

In a simple displacement of benzyl isonitrile by K14CN from II, all the labeled atoms should appear in the isonitrile complex and none in the benzyl isonitrile. But the label was present in all of the products isolated and in each to a different extent. For example, the benzyl isonitrile was more radioactive than the N-benzyl formamide which must have been formed by addition of water to benzyl isonitrile. The results indicate that the internal isomerization (III V, Equation 7), the generation of benzyl isonitrile and N-benzyl formamide, and the polymerization of benzyl isonitrile are concomitant reactions. 

Below the temperatures for the NTC regime, the peroxy radical (ROO) may be involved in a chain-branching sequence of reactions that is responsible for the positive temperature dependence. The oxidation rate varies significantly between different hydrocarbons or hydrocarbon isomers, depending on their structure. The first step is an internal isomerization,... 

The hydrogen-exchange reaction between C2H4 and C2D4 via ethyl intermediates is the same type of reaction as the cis-trans isomerization reaction of 2-butene, because these reactions both involve the elementary processes of alkyl intermediate formation followed by internal rotation around C—C bonds, as described in Scheme 5. Then the hydrogen exchange... 

HO-initiated oxidation of the alkanes become complex with increase in carbon number. Namely, a large variety of alkyl radicals can be produced by the H-atom abstraction from the primary, secondary and tertiary C—H bonds in the parent alkane [88]. The resulting ROO ( C4) radicals have been shown by Atkinson et al. to yield R0N02 as well as RO + N02 upon reaction with NO [100-102]. A major complication in the alkane oxidation mechanism arises from the variety of competitive reaction channels that RO radicals can undergo, e.g., 02-reaction, unimolecular dissociation and internal isomerization. There have been a number of experimental and theoretical studies of these reactions [31,88]. 

The performance of the method, recently proposed by Neshev and Mineva for the computation of internal chemical hardness tensor and other reactivity indices, was investigated considering different systems and three isomerization reaction paths. Results indicates that ... 

Lead tetra-acetate oxidation of the allylic alcohols (170)—(172) and (182) leads to the formation of the epoxides (183)—(186), products of a novel internal addition reaction of the electron-deficient alcohol oxygen to the allylic double bond. In some cases, (171) and (172), the formation of a new type of acetoxylated enol ether (173) and (174) is observed. Oxidation of the allylic dienols (175) and (176) gives the epoxyacetates (187) and (188). A variety of cyclization products was also isolated. Their formation requires an isomerization of the allylic trans double bond to cis.69 Lead tetra-acetate oxidation of dihydro-y-ionol (189) gives the new bicyclic ether... 

All isomerization reactions eventually reach their thermodynamic equilibrium, but it is sometimes possible to favour a particular isomer, for example internal alkenes can be made to give the terminal aldehydes in hydroformylation... 

An alternative explanation is that reforming the alk-1-ene involves breaking a primary C-H bond, which requires more energy than breaking a secondary C-H bond, to form the (Z)-alk-2-ene. If the isomerization reaction is allowed to continue, eventually, by repetition of the catalytic cycle shown in Scheme 2, the alk-1-ene will be further converted into a mixture of alk-2-enes and alk-3-enes. The equilibrium is only slowly achieved because the low-binding constants of internal alkenes make it difficult for them to enter the catalytic cycle. 

The important concentration-time profiles include those for 1,2- and 2,3-epoxybutane, 2-methyloxetan, tetrahydrofuran, butyraldehyde and 2-butanone, the relative concentrations of these products being determined by the relative rates of 1- and 2-butylperoxy radical isomerization and decomposition. The kinetic data used to represent these reactions were the parameters recommended by Walker [229] in 1961. The formation of butyraldehyde and 2-butanone require internal isomerizations of the form... 

Figure 13. A typical time evolution of the three gyration radii, a, a2, and CI3 (a > ct2 > 03) (a), and the three hyper-angles, 3( ) (b). Structural isomerization reaction has taken place two times in this example by crossing the planar structures as indicated by the condition 3 = 0. Total internal energy is E = —4.1e.

O group in the molecule. The internal rotation around the C-O and O-N axes of CH2=CHONO leads to its four isomers. The relative differences in total energy of the respective stereoisomers are small. Therefore, only the most stable structures of the adducts were taken into account in describing the reaction kinetics. The energy levels in the figure correspond to those structures only. The potential energy profile shows that the nitroso-adduct may also be formed by the isomerization reaction... 

An isomerization reaction has the simple form A —> B. Assuming that operating conditions and the condition of the catalyst are such that the external- and internal-diffusion steps have negligible concentration gradients, propose rate equations for the following cases ... 

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