Isomerization reactions with

Isomerization has been observed with many a,j3-unsaturated carboxylic acids such as w-cinnamic 10), angelic, maleic, and itaconic acids (94). The possibility of catalyzing the interconversion of, for example, 2-ethyl-butadiene and 3-methylpenta-l,3-diene has not apparently been explored. The cobalt cyanide hydride will also catalyze the isomerization of epoxides to ketones (even terminal epoxides give ketones, not aldehydes) as well as their reduction to alcohols. Since the yield of ketone increases with pH, it was suggested that reduction involved reaction with the hydride [Co" (CN)jH] and isomerization reaction with [Co (CN)j] 103). A related reaction is the decomposition of 2-bromoethanol to acetaldehyde... 

Previous studies have concluded that 4-, 5-, and 6-coordinate W species are present on AI2O3 and Ti02 supports [17,30] depending on surface W density and on hydration state. The present study has detected W03-like distorted octahedral domains at all surface densities and irrespective of hydration on Zr02. These species catalyze alkane isomerization reactions with much higher turnover rate and selectivity than dispersed WOx moieties on alumina or titania. 

The experimental data on free radical isomerization reactions with H-atom abstraction were analyzed by the IPM method [36]. The kinetic parameters of isomerization were compared with those of the intermolecular H-atom abstraction (see Chapter 2). The results... 

In conclusion to this section, the two step reaction requires the presence of a metal that can be easily oxidized (d8 over d6). However the 1,3 migration step does not appear to be easy in an intramolecular way. An intermolecular 1,3 shift seems feasible but is probably highly sensitive to steric effects. The pathways for the isomerization reactions with d6 and d8 metal complexes are significantly different. They have in common the preference for the hydrogen to move as a proton, whether the shift starts from Ca or from the metal center. 

Hydrocarbons higher than C3 can also undergo isomerization on Pt, running in parallel to hydrogenolysis. With butane or isobutane the selectivity for isomerization is rather low, also on Pt, but the higher hydrocarbons show more of isomerization reactions. With higher hydrocarbons some other metals (Ir, Pd) also show some isomerization selectivity. 

Let us consider a model catalytic isomerization reaction with the detailed mechanism... 

Examples of such reactions obtained with pure compounds are shown in Table V. Isomerization reactions with tungsten sulfide catalysts are... 

A beautiful classical theory of unimolecular isomerization called the reactive island theory (RIT) has been developed by DeLeon and Marston [23] and by DeLeon and co-workers [24,25]. In RIT the classical phase-space structures are analyzed in great detail. Indeed, the key observation in RIT is that different cylindrical manifolds in phase space can act as mediators of unimolecular conformational isomerization. Figure 23 illustrates homoclinic tangling of motion near an unstable periodic orbit in a system of two DOFs with a fixed point T, and it applies to a wide class of isomerization reaction with two stable isomer... 

Examination of the alkylperoxy radicals which may be formed from 3-ethylpentane, 3-methylpentane and 2-methylpentane shows that, in each case, some may undergo isomerization reactions with relatively low activation energies [58], examples of which are shown in Table 20. 

Isomerization reactions with diene monomers are very rapid in tetra-hydrofuran at room temperature [28, 29]. Within a few minutes, extensive isomerization has occurred and it is difficult to measure the rate of monomer addition to the normal anions. These processes are much slower at lower temperatures [30]. 

Figure 6. Variation of equilibrium conversion and yield of 1-hexene isomerization reactions with temperature. (Reprinted with permission from ref. 8. Copyright 1988 Pergamon.)...

Figure 3 compares the rate values of these isomerization reactions with the 1-decyl radical -decomposition ... 

FIGURE 7.2 An isomerization reaction with two parallel paths a direct path D (a —>b), and a mediated path Mt (a + c —> ac), M2 (ac —>b + c). In the first diagram (A), the rate of D and M2 D, thus path M bypasses the direct path D, and c accelerates a through the system, acting as a catalyst (reaction rates indicated by arrow thickness). In the second diagram (B), the rate of Mj D, but in this case D M2, thus c locks up a in complex ac, acting as a competitive inhibitor. 

CDPIO-Mg California problem. Isomerization reaction with catalyst decay. [3" ed. PlO-Sy Review the data and make a recommendation,... 

The PES calculated at the G2M (CC2)//PW91PW91/6-311-i-G(3df) level is shown in Fig. 11. The key structures of species involved in this reaction are shown in Fig. 12. TSl is the transition state for the OCIO ClOO isomerization reaction with a barrier of 63.3 kcal/mol, whereas TS2 is that for the CIO O C10 0 isomerization with a barrier of 61.5 kcal/mol. Predicted rate constants for the production of O + CIO and Cl + O2 resulted directly from the unimolecular decomposition processes with no contributions from the isomerization reactions. Comparison of the predicted ClOO decomposition rate with experimentally available values is shown in Fig. 13. The low- and high-pressure rate constants for OCIO and ClOO dissociations can be expressed by ... 

Alkoxy radicals that arise from the reaction of NO with alkylperoxy radicals also may enter into several competing processes. Four such reactions must be considered thermal decomposition, isomerization, reaction with oxygen, and addition to either NO or N02. Falls and Seinfeld (1978) have presented a brief review of the various possibilities. Table 6-13 summarizes current information on rate coefficients and projected rates in the atmosphere for several small alkoxy radicals. 

Hydride complexes of platinum have received considerable study since the preparation of PtHCl(PEt3)2- Spectroscopic studies by NMR techniques have been widely used because of the structural information which can be obtained from coupling constant data to Pt and other nuclei. Platinum is widely used as a heterogeneous catalyst, and vibrational studies on platinum hydride complexes have been useful for comparison of a hydrogen atom bonded to a single platinum with that bonded to a surface. Complexes of platinum have been used to catalyze hydrogenation, hydrosilylation and isomerization reactions with alkenes and alkynes, as well as H/D exchange reactions on alkanes. Hydride complexes are frequently proposed as intermediates in these reactions, and the pathways related to the known chemistry of hydride complexes. 

Guggenheim s method for the analysis of kinetic data is useful for situations in which the initial concentrations of reactants are not known or are inaccessible. This method is generally regarded as applicable only to cases in which the rate expression obeys first-order or pseudo first-order kinetics. However, it is also possible to extend Guggenheim s analysis to reversible reactions that are first-order (or pseudo first-order) in both the forward and reverse directions. Consider as an example the generic isomerization reaction with mechanistic equations of the form... 

It is interesting that m-isomer is the only product of isomerization reaction with a very little trace of o-isomer. The absence of o-DIPB, it might have been predicted on steric grounds. 

Table 20.1 Experimental studies of low-barrier isomerization reactions with intrinsic non-RRKM dynamics.

Asano and co-workers studied the effect of pressure on the thermal Z—> isomerization of 4-(dime-thylamino)-4 -nitroazobenzene in an effort to test the effect of bulk viscosity of the medium on isomerization reactions with respect to reaction rate theories. ... 

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