Evans Model

The Evans Model. It is known that (Z) enolates are more stereoselective than ( ) enolates even when r1 is not large. The Zimmerman-Traxler model transition states 352-355 do not account for this observation. It has been suggested that the transition states are not chair-like, but skewed, as in 381-384.221 In this representation (Z) enolate 381 leads to the syn aldol. Similarly, (Z) enolate 382 gives the anti aldol, ( ) enolate 383 give the anti aldol and E) enolate 384 is the precursor to the syn aldol. The major steric interactions in this model are those for r1 r3 and r2 - r3. For both (Z) and E) enolates, the r1 r3 interaction favors 381 and 383, respectively. The r2 r3 interaction is more important for the E) enolate and 

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Rouson, D., S.R. Tieszen, and G. Evans, Modeling convection heat transfer and turbulence with fire applications A high temperature vertical plate and a methane fire, in Proceedings of the Summer Program. 2002, Center for Turbulence Research, Stanford University, pp. 53-70. 

Molecules as ionic aggregates. The Lapworth-Evans model... 

The reaction of ( /Z)-2-butenyltri-n-butylstannane with aldehyde 44, as reported by Keck and coworkers 2 occurred with 1,3-asymmetric induction to yield 45 via the synclinal arrangement, illustrated from the Evans model 46 (Scheme 5.2.11). 

For atmospheric wet-dry corrosion cycles, we have the well-known Evans model [93], in which the wet corrosion couples the anodic iron dissolution with the cathodic ferric oxyhydroxide reduction into magnetite ... 

A.V. The Noyori Open-Chain Model. In the Mukaiyama reaction, the Zimmerman-Traxler and Evans models are not satisfactory for predicting diastereoselectivity. Several open (nonchelated) transition states have been considered as useful models. The condensation reaction of carboxylic acid dianions with aldehydes indicated that anti selectivity increased with increasing dissociation of the gegenion (the cation, M+),224 When analyzing an aldol condensation that does not possess the bridging cation required for the Zimmerman-Traxler model, an aldehyde and enolate adapt an eclipsed orientation as they approach. Noyori reported syn selectivity for the reaction of a mixture of (Z)-silyl enol ether 389 and ( )-silyl enol ether 390 with benzaldehyde in the presence of the cationic tris-(diethylamino) sulfonium (TAS).225 xhis reaction is clearly a variation of the Mukaiyama reaction, which does not usually proceed with good diastereoselectivity... 

Square planar Evans model for Diels-Alder addition... 

Figure 8.3 Corey and Evans models for asymmetric induction...

To obtain the thermal force and dimer equilibrium constant eq using the Evans model, the most probable rupture force between the binding motifs is usually measured for various loading rate. By utilizing the theory of Evans and Williams, Vancso et al. found that those parameters can be obtained even with one data set at a single loading rate. The value of the dimer equilibrium constant obtained for UPy-UPy dimers in hexadecane agrees very well with the value of eq 1 x 109 M predicted by previous studies with bulk measurements [140]. 

Under the aforementioned hypotheses, as two different crystalline phases are formed (a and mesomorphic), at least two kinetic processes take place simultaneously. The simplest model is a parallel of two kinetic processes non-interacting and competing for the available molten material. The kinetic equation adopted here for both processes is the non-isothermal formulation by Nakamura et al. (Nakamura et al., 1973, Nakamura et al., 1972) of the Kolmogoroff Avrami and Evans model (Avrami, 1939,1940,1941, Evans, 1945). 

Similarly, the interaction between a resorc[4]arene cavi-tands and tip-immobilized (tetraorganyl) ammonium guests was studied. The flexible polymer linker ensured that the interaction took place as an identifiable single-molecule interaction. As shown in Figure 10, the most probable rupture force depended logarithmically on the loading rate, in accordance with the Kramers-Bell-Evans model. Ammonium and trimethyl substituted ammonium could be well differentiated. 

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