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Sole transitional process

In the following, we will use solely the Allan variance to further inquire into the nonstationarity of the multibasin transition processes on many-dimensional protein landscapes. [Pg.275]

C3 and higher) can be influenced in insertion polymerization by the ligands attached to the transition metal complex. This gives controlled access to isotactic or syndio-tactic polymers, an achievement that has drastically expanded the application fields of polypropylene in recent years. Insertion polymerization is particularly suitable for polymerization of ethylene (with or without higher 1-olefins as co-monomers), pro-pene, butene, and styrene. Section 6.20 is devoted solely to processes for production of polyethylene, describing details of the mechanism of insertion polymerization and process parameters. [Pg.497]

In the framework of this ultimate model [33] there are m2 constants of the rate of the chain propagation kap describing the addition of monomer to the radical Ra whose reactivity is controlled solely by the type a of its terminal unit. Elementary reactions of chain termination due to chemical interaction of radicals Ra and R is characterized by m2 kinetic parameters k f . The stochastic process describing macromolecules, formed at any moment in time t, is a Markov chain with transition matrix whose elements are expressed through the concentrations Ra and Ma of radicals and monomers at this particular moment in the following way [1,34] ... [Pg.176]

Recently, an example of cycloamylose-induced catalysis has been presented which may be attributed, in part, to a favorable conformational effect. The rates of decarboxylation of several unionized /3-keto acids are accelerated approximately six-fold by cycloheptaamylose (Table XV) (Straub and Bender, 1972). Unlike anionic decarboxylations, the rates of acidic decarboxylations are not highly solvent dependent. Relative to water, for example, the rate of decarboxylation of benzoylacetic acid is accelerated by a maximum of 2.5-fold in mixed 2-propanol-water solutions.6 Thus, if it is assumed that 2-propanol-water solutions accurately simulate the properties of the cycloamylose cavity, the observed rate accelerations cannot be attributed solely to a microsolvent effect. Since decarboxylations of unionized /3-keto acids proceed through a cyclic transition state (Scheme X), Straub and Bender suggested that an additional rate acceleration may be derived from preferential inclusion of the cyclic ground state conformer. This process effectively freezes the substrate in a reactive conformation and, in this case, complements the microsolvent effect. [Pg.247]

Transition metal-catalyzed intermolecular [2 + 2 + 2] cyclotrimerization of alkynes to benzene derivatives has been extensively studied. In this section, the focus is on the cyclo-trimerizations of the substrates bearing three independent unsaturated bond components. The key issue with this type of process usually involves the challenge of controlling regioselectivity [1—1]. However, 1,3,5-trisubstituted benzene 44 can be obtained as the sole product in good yield when 3-butyn-2-one 43 is used as the substrate for the cyclotrimerization catalyzed by Rh2(pfb)4 (pfb=perfluorobutyrate) in the presence of EtsSiH under a CO atmosphere (Eq. 11) [30]. [Pg.138]

Surely a 480 percent increase in the number of psychiatric abnormalities over fifty years cannot result solely from dispassionate scientific discovery. The transition from disorder to disease and the proliferation of such diseases are more a function of cultural, economic, and political processes than scientific advances. In fact, the sharpest critics of psychiatry s current stance maintain that, except for a few major psychotic illnesses, there is no evidence that the multiplication of conditions listed as brain diseases in the DSM warrant that designation. [Pg.212]

At a high cathodic potential (region II), a sharp transition is observed at the potential referred to as ET. The authors demonstrate that the sudden increase of the electrode kinetics could not be attributed to the sole electrochemical reduction of the electrode material, nor to the electrolyte reduction. They conclude that after the transition, the main electrode process is still an oxygen electrode reaction with a major change of mechanism, leading to the onset of an important electrocatalytic effect. This assertion is sustained by the analysis of ... [Pg.108]

Balzani et al. prepared dendrimers with metal complexes serving both as core [36] and as branching unit The metallodendrimer in Fig. 2.10 is constructed solely from polypyridine ligands and transition metal ions. Such dendritic transition metal complexes can be synthesised both convergently and divergently and different transition metal ions (ruthenium/osmium) can be incorporated. This provides a means of influencing the luminescence properties of the den-drimer. Thus the energy transfer process proceeds from the inside outwards in... [Pg.34]

Solvents are selected such that some will escape relatively quickly from paint films to prevent excessive flow, while others will escape slowly to provide film leveling and adhesion. With typical alkyd coatings, the first 30% of solvent has been observed to evaporate as quickly as the neat solvents, essentially at a constant rate which is dependent on volatility. Later stage evaporation occurred several times more slowly and was rate-controlled by solvent diffusion to the surface of the paint film. The transition point between this behavior was defined as the resin solids content at which the evaporation rate due to volatility equaled that due to diffusion. Transition points have been observed to typically occur at a resin solids content of 40-50% v/v. Thus alkyd paints, normally formulated at 27-40% v/v resin solids, generally exhibit rapid initial solvent-release driven by volatility while high solids coatings (usually 65-75% v/v resin solids) dry solely by a diffusion-controlled process with negligible influence by solvent volatility (Ellis, 1983). [Pg.384]

The sole factor determining the value of a rate or equilibrium constant is the difference in free energy between the reactants and either a transition state, in the case of a reaction rate, or the products, in the case of an equilibrium. Rate and equilibrium constants cannot therefore properly be correlated with any static property of the reactants themselves. This point cannot be emphasized too strongly in view of the many attempts that have been made to find such correlations. One might add that attempts of this kind are in any case basically unsatisfactory in that they ignore the transition state entirely and so can throw no light on its structure even if correlations of this kind can be established, they do not throw any light on the detailed mechanism of chemical process—and it is just in this field that quantum theory has most to offer to chemists. [Pg.102]

Donor/acceptor-substituted carbenoids are usually much more chemoselective than the more established carbenoids functionalized solely with acceptor groups [lc]. The development of these donor/acceptor-substituted carbenoids has enabled enantioselective intermolecular C-H insertions to become a very practical process. These carbenoids have a strong preference for functionalizing C-H bonds where positive charge build-up at C in the transition state is favored but these electronic effects are counter-balanced by steric factors. Benzylic and allylic sites and C-H bonds adjacent to oxygen and nitrogen functionality are favored but these sites can also be sterically protected if desired. By appropriate consideration of the regiocontrolling elements, effective intermolecular C-H insertions at methyl, methylene, and methine sites have been achieved. [Pg.627]


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Soled

Transition processes

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