Promising Reaction Systems

In the past 3 years, several research groups have actively searched for chemical reaction systems capable of the rather stringent requirements for laser operation discussed in Section 3.4.1. Most emphasis has been placed upon atom-exchange reactions of the type 

Metal Metal oxide Dissociation energy, kcal/mole Metal (ground state) Metal oxide (ground state) Dissociation energy, kcal/mole 

In the search for selective excitation of reaction products, consideration has been given to reactions which lead to products with electronic ground states that do not adiabatically correlate with reactant states. A few examples of such reactions are listed in Table 3.6. In a given reaction system, however, complications such as nonadiabatic transitions, energy barriers, and E - V transfer processes may be of sufficient importance that conventional adiabatic correlations may be of limited use. 

Another way to characterize prospective diatomic reaction products has been considered by Sutton and Suchard. In this approach diatomic 

The electronic states of many reaction products consist of two spin-state manifolds. Intercombination transitions in such products may have favorably long radiative lifetimes. A few examples of such reaction systems are given in Table 3.7. 

---

Functionalized polyelectrolytes are promising candidates for photoinduced ET reaction systems. In recent years, much attention has been focused on modifying the photophysical and photochemical processes by use of polyelectrolyte systems, because dramatic effects are often brought about by the interfacial electrostatic potential and/or the existence of microphase structures in such systems [10, 11], A characteristic feature of polymers as reaction media, in general, lies in the potential that they make a wider variety of molecular designs possible than the conventional organized molecular assemblies such as surfactant micelles and vesicles. From a practical point of view, polymer systems have a potential advantage in that polymers per se can form film and may be assembled into a variety of devices and systems with ease. 

Further progress will undoubtedly involve the preparation of more generally applicable effective reagents, for example for the reduction of dialkyl ketones. Further systematic studies of promising reducing systems as well as increased knowledge of the actual species formed in the reaction of LAH with chiral reagents will be valuable. 

One of the landmark achievements in the area of enantioselective catalysis has been the development of a large-scale commercial application of the Rh(I)/BINAP-catalyzed asymmetric isomerization of allylic amines to enamines. Unfortunately, methods for the isomerization of other families of olefins have not yet reached a comparable level of sophistication. However, since the early 1990s promising catalyst systems have been described for enantioselective isomerizations of allylic alcohols and aUylic ethers. In view of the utility of catalytic asymmetric olefin isomerization reactions, I have no doubt that the coming years will witness additional exciting progress in the development of highly effective catalysts for these and related substrates. 

Abstract The fracture properties and microdeformation behaviour and their correlation with structure in commercial bulk polyolefins are reviewed. Emphasis is on crack-tip deformation mechanisms and on regimes of direct practical interest, namely slow crack growth in polyethylene and high-speed ductile-brittle transitions in isotactic polypropylene. Recent fracture studies of reaction-bonded interfaces are also briefly considered, these representing promising model systems for the investigation of the relationship between the fundamental mechanisms of crack-tip deformation and fracture and molecular structure. 

Scale-up of promising reactions from microliters to 2.5 liters can be accomplished in the same system... 

New and promising developments can be seen in high-intensity (2-photon) laser photolysis, in the combination of fields and radiation (see Chap. 3), in exploitation of the coherence properties (see Chap. 2), and in the detection of more autocatalytic or autoinductive reaction systems. 

The continuing studies on the mechanisms involved in zeolite synthesis are leading to a better understanding of the controlling factors in this complicated reaction system. But more remains to be done. This also holds the promise of leading to the synthesis of new zeolitic structures. 

In the proposed two-step process, it is important to attain high efficiencies for conversion of coal to COx (CO -I- CO2) in the first-step reaction and then for conversion of CO2 to CO in the second-step reaction by an external heat input. From the thermodynamic conditions and the low cost, the redox pair of Fe304/a-Fe was one of the promising redox systems for the two-step process, but it still required the operating temperature above 1200°C[2]. It is well known that many kinds of metal ions can be incorporated into the spinel lattice structure of magnetite by replacing ferrous or ferric ions. There is the possibility that metal-substitution for Fe or Fe " in magnetite causes a phase transition to the metallic phase, which proceeds readily even at low temperatures and improves the conversion efficiencies of coal and CO2 to CO in the two-step process. 

---