Inversion of selection

The enantioselective hydrosilylation catalyst system based on the chiral pre-catalyst dichloro l- (/ )-l- [(S)-2 (dipheaylphosphinoKP) ferrocenyl] ethyl -3- trimethyl- phenyl-5-1 H- pyrazole-tc/V) palladium, 1 (shown in Figure 2) exhibits a interesting inversion of selectivity with a series of para-... 

Recognition in the Systems of Polymer—Two Oligomers Type Inversion of Selection... 

Several of preparations of aziridines have been reported. The aza-Darzens reaction of an fV-bromoacylcamphorsultam with iV-diphenylphosphinylimines, ArCH=N—P-(=0)Ph2, gives cz s-aziridine derivatives, except if the aryl is o-substituted, which gives significant trans product, and even 100% trans- with o-CF3.61 While steric (g) factors play a role in this inversion of selectivity, electronic effects are also important o-methyl gives a 50 50 ratio of products. 

The complexity of xylene adsorption over zeolites is too high to predict the selectivity from the chemical properties of the zeolite only (electronegativity of the cations, charge of the framework oxygens). The interactions between xylenes and the zeolite must necessarily be considered, which explains the important development of molecular simulation methods. This is supported by the work of V. Lachet et al. (18) who succeeded in reproducing the inversion of selectivity between KY and NaY with Grand Canonical Monte Carlo Simulations. 

Reactions of 3-te/V-butylcyclohexene with, e.g., acetyl hypobromite, hypobromous acid and /V-chlorosuccinimide show diastereoselectivity in the electrophilic attack similar to that observed in the epoxidation (trimsIds obsd 90 10 calcd 77 23168), with the expected overall inversion of selectivity of epoxide formation, to give ct.y-6109. 

The permeability for pervaporation depends on the concentrations of permeants in the polymer, which can cause swelling and solute-interaction effects in polymers. Inorganic membranes have recently been used in this application to overcome some of these limitations. Because of these non-ideal effects, the selectivity can be a strong function of feed concentration and permeate pressure, causing inversion of selectivity in some cases. 

A most significant aspect of the product distribution is that it is possible to control the selectivity to afford branched-chain compounds. Figure 19 is a plot of the fraction of branched-chain species present in the C4 and C5 alditols produced versus conversion of formaldehyde. Rates of 780 to 940 and 150 to 350 mmoles of HCHO feed per liter per min at 60° and 32.5 mmoles of HCHO feed per liter per min at 40° are shown. Figure 19 exhibits a remarkable inversion of selectivity. At 50% (and lower) con-... 

In the same context, Claramunt [51] reported complete inversion of selectivity in the reaction between 1-bromoadamantane (28) and pyrazole (27). When the reaction is performed in an autoclave at 230 °C the exclusive product is 4-(l-adamantyl)pyrazole (29), but when the reaction is conducted in a microwave reactor the corresponding 3-substituted isomer 30 (44%) is obtained in high purity (Scheme 5.10). 

HT transporter. The potencies and selectivity indices of venlafaxine and its regio isomer (3-MeO) are identical. The regio isomer (3-CFg) of the 4-CF3 compoimd however shows an inversion of selectivity from the 5-HT transporter to the NE transporter. 

While with h s-Cinchona derivatives this rule regularly works with all catalyst concentrations, with natural alkaloids it is necessary to keep the concentration of catalyst free base at a high level. The catalyst-product complex (salt) formed during the reaction is still catalytically active and, while with succinic anhydrides enantiopurity is drastically lowered, with glutaric anhydrides an inversion of selectivity occurs. This problem can be solved by the addition of an achiral, sterically hindered auxiliary base (e.g. pempidine). ... 

Scheme 1 Inversion of selectivity with mixing order in ether...

Figure 25. Inverse of selective reflection maxima (o=p) as a function of composition for a number of binary chiral nematic mixtures. Here the components are O cholesteryl formate/cholesteryl chloride (at 50 °C), A cholesteryl propionate/cholesteryl chloride (at60°C), cholesteryl heptanoate/cholesteryl chloride (at 60 °C), A cholesteryl laurate/cholesteryl chloride (at 60°C) [105],...

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