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Regioselective adsorption

Keyword fabrication, silane layer, colloid particle, polym latex, regioselective adsorption, deposition, particle pattern, self-assembly... [Pg.772]

The stereospecificity, stereoselectivity, and regioselectivity of the fluoroacetamidation of a variety of olefins have been studied in detail from synthetic and mechanistic aspects by Laurent and coworkers, as in Eq. (51) [331-334]. The significant stereochemical results observed may be rationalized by considering coplanar adsorption on the anode of carbo-nium cation intermediates derived from the olefins. [Pg.1077]

An enhancement of the regioselectivity was observed when the catalyst modifier concentration was increased (Figure 3). The enhancement might be caused by 1) the modifier-reactant interaction in the liquid-phase, 2) the modifier-reactant interaction on the catalyst surface, 3) the coverage dependent adsorption modes of the reactant and modifier or a combination of factors 1-3. [Pg.363]

To summarize, the enhancement in regioselectivity, due to the small amount of modifier added, was interrelated with the enantioselectivity (cjf) and can be most plausibly explained by similar interactions on the catalyst surface which are responsible for the enantiodifferentiation. The substrate-modifier interaction on the catalyst surface coupled with the coverage dependent adsorption modes of the modifier and reactant explain the enhancement of rs as well as es and their dependence on modifier concentration. In the light of presented data it is evident that one needs to incorporate the coverage dependent adsorption modes in the kinetic model for a correct description of the rs and es, otherwise the maximum in selec-tivities and selectivity dependence on modifier concentration caiuiot be described. [Pg.364]

The enhancement of rs was strongly interrelated with the enantiomeric excess and was explained by the interactions between reactant and modifier on the catalyst surface. Interactions responsible for the enantiodifferentiation result also in the enhancement of regioselectivity. The coverage dependent adsorption modes of the modifier and reactant are responsible for the dependence of the rs and enan-tioselectivity on the modifier concentration. [Pg.365]

The stereochemistry of the products and the regioselectivity of the coupling reaction indicates that adsorption of saturated alkyl radicals is relatively unimportant [20]. Carboxylates which are chiral and non-racemic at the a-position totally lose their optical activity in mixed heterocoupling [21, 22]. This racemization indicates either a free radical as intermediate or its fast desorption-adsorption at the anode. These findings are further supported by the decarboxylation of 3 and 4, which both form the same 1 2 1 mixture of transfrans-, cis,trans- and c ,c -coupled dimer, whilst 5-7 show a slight diastereoselectivity [23, 24]. The latter could be due to some adsorption caused by the phenyl group or double bond and/or by a more effective facial shielding of the radicals (see Chapter 3.3). [Pg.260]

Kurita et al. (1988) have synthesized regioselective Af-nonanoyl chitosan and reached a conclusion that acylation enhances the adsorption capacity, and the capacity increases from 75% of chitosan to 98% of nonanoyl chitosan. [Pg.510]

Selectivity improvement is a critical requirement for industrial applications of lipase. This includes substrate selectivity, stereoselectivity, regioselectivity, and enantio-selectivity. Adsorption of Candida rugosa on celite was reported to enhance the stability of lipase and improve its enantioselectivity up to 3-fold (Ogino, 1970). Entrapment in cellulose acetate-Ti02 gel fiber improved the selectivity of Rhizomucor miehei lipase in the hydrolysis of 1,2-diacetoxypropane (Ikeda and Kurokawa, 2001). Also the enantioselectivity of pegylated P. cepacea lipase was increased 3-fold by... [Pg.48]

Bromination of Allylic Alcohols. Sflica gel-supported copper(n) bromide has been used for the regioselective bromi-nation of methyl 3-hydroxy-2-methylenepropanoates and 3-hydroxy-2-methylenepropanenitriles (eq 13). In the absence of silica gel, no reaction occurs between CuBr2 and these substrates, while adsorption onto AI2O3, MgO, or Ti02 leads to side reactions rather than the clean allylic bromination observed with CuBr2/Si02. The reaction is stereoselective with respect to formation of the (Z) isomer. [Pg.192]


See other pages where Regioselective adsorption is mentioned: [Pg.772]    [Pg.773]    [Pg.778]    [Pg.772]    [Pg.773]    [Pg.778]    [Pg.97]    [Pg.192]    [Pg.59]    [Pg.77]    [Pg.192]    [Pg.539]    [Pg.347]    [Pg.725]    [Pg.27]    [Pg.226]    [Pg.434]    [Pg.2645]    [Pg.246]    [Pg.637]    [Pg.87]    [Pg.901]    [Pg.156]    [Pg.358]    [Pg.362]    [Pg.259]    [Pg.259]    [Pg.135]    [Pg.104]    [Pg.193]    [Pg.611]    [Pg.240]    [Pg.152]    [Pg.33]    [Pg.183]    [Pg.421]    [Pg.77]    [Pg.186]    [Pg.393]    [Pg.394]   
See also in sourсe #XX -- [ Pg.772 ]




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