Redistribution During Reaction

This work has recently been extended, again with a single Pd/Al2O3 catalyst pellet 69). The image time was reduced to 34 s by introduction of manganese ions into the 

To date there have not been any reports of chemically resolved images within oxide-supported catalysts—the signal in the preceding example did not differ- 

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Chemical reactions are first classified according to the minimal number of valence electrons that must be redistributed during the conversion of the educts into the products this is their minimal chemical distance (MCD). The determination of the MCD of a chemical reaction (ref. 5-7) yields also an atom-by-atom mapping of the educts and the products, and it also identifies the reactive centers whose union is the socalled core of the reaction. 

As emphasized earlier, the redistribution or transfer of hydrogen is one of the most dominant and recurrent reactions of olefins in the presence of acidic zeolite catalysts. The formation of hydrogen-rich paraffins and hydrogen-deficient aromatics is superimposed constantly on any reaction where a low molecular weight olefin—or olefin precursor — is either a reactant, a product, or an intermediate. Even more specifically, numerous examples of hydride-transfer processes during reactions over zeolite catalysts have been observed, and we will discuss some of these in detail. 

Redistribution during thermal processing is a common self-reaction in condensation polymers such as PA, PEST, and PC that often contain nucleophilic amine, hydroxy, or phenolic end-groups, along with electrophilic groups such as amide, ester, or carbonate linking the individual monomer units. 

Polydisilylazanes have been synthesized by the reaction of mixed disilanes with hexamethyldisilazane through silicon-chlorine/silicon-nitrogen bond redistribution reactions [10,26]. The formula [(CH3)2.6(Si2)i.oNHi.5]n was deduced during (reaction) at 250°C. 

Quack M 1991 Mode selective vibrational redistribution and unimolecular reactions during and after IR-laser excitation Mode Selective Chemistry ed J Jortner, R D Levine and B Pullman (Dordrecht Kluwer) pp 47-65... 

Such layer structure does not allow ns to say a priori that hybridization of DNA will be possible, for it is protected by the octadecylamine layer. In order to control for this possibility, fluorescence measurements were performed. The first indication that hybridization was successful is that after the process, the sample surface became wettable, while before it and after cold hybridization it was not wettable at all. The results of the fluorescence measurements are summarized in Table 10. The results of the specific hybridization are three times more with respect to unspecific hybridization and one order of magnitude more with respect to cold hybridization. Thus, it appears that during a normal hybridization (100% homology) some structural changes and redistribution of the layer takes place. As a result, DNA becomes available for the specific reaction. Such a model also explains why the fluorescence level after unspecific hybridization (10% homology) is higher with respect to cold hybridization. Because the molecules have some mobility when the film is warmed, some DNA from the film could be hybridized on itself, while during cold hybridization this is impossible. 

A unique characteristic of polyesters is their ability to undergo additional condensation reactions during processing or when in the solid state. These reactions redistribute the molecular weight of the polymer until a dynamic equilibrium is established. Water, when present at high temperatures in polyester melts, can depolymerize polyesters via a hydrolysis reaction. For this reason, manufacturers must carefully dry the polymer before processing. 

Cyclopropanes in low yield were first noted in 1964 by Banks and Bailey (12) during the disproportionation of ethylene, but little significance was attached to that observation until recently, because such products had no obvious relevance to early mechanistic concepts based on pairwise rearrangements of bisolefin complexes. However, the subsequent adoption of carbenelike species as metathesis intermediates (4) provided a foundation for later development of cyclopropanation concepts. The notable results of Casey and Burkhardt (5) made an impact which seemed rather neatly to unify mechanistically the interconversion of cyclopropanes and metathesis olefins, although the reactions which they observed were stoichiometric rather than catalytic [see Eq. (4)]. Nevertheless, their work indicated a net redistribution of =CPh2 and =CH2 from (CO)5W=CPh2 and isobutylene, respectively, to form CH2=CPh2. Dissociation and transfer of CO yielded W(CO)6. Unfortunately, the fate of the isopropylidene moiety remained unknown. In 1976,... 

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