Directed synthetic method

Any study of colloidal crystals requires the preparation of monodisperse colloidal particles that are uniform in size, shape, composition, and surface properties. Monodisperse spherical colloids of various sizes, composition, and surface properties have been prepared via numerous synthetic strategies [67]. However, the direct preparation of crystal phases from spherical particles usually leads to a rather limited set of close-packed structures (hexagonal close packed, face-centered cubic, or body-centered cubic structures). Relatively few studies exist on the preparation of monodisperse nonspherical colloids. In general, direct synthetic methods are restricted to particles with simple shapes such as rods, spheroids, or plates [68]. An alternative route for the preparation of uniform particles with a more complex structure might consist of the formation of discrete uniform aggregates of self-organized spherical particles. The use of colloidal clusters with a given number of particles, with controlled shape and dimension, could lead to colloidal crystals with unusual symmetries [69]. 

In many cases, however, a cluster in a particular oxidation state is not accessible by direct synthetic methods using simple ligands or by straightforward oxidation or reduction of the cluster product. Solutions that have been developed for this problem include the use of sterically hindered ligands or ligands with varied donor atoms. 

Despite growing importance of axially chiral biaryls as chiral auxiliaries in asymmetric synthesis, direct synthetic methods accessing to the enantiomerically enriched biaryls from achiral precursors are still very rare, Application of asymmetric cross-coupling to construction of the chiral biaryls is one of the most exciting strategies to this goal. The reported application... 

One of the most attractive features of monolayer-protected AuNPs is the possibility for facile introduction of a wide variety of different thiolated molecules into the ligand shell. This may be achieved using different strategies (1) direct synthetic methods,97 124 170 (2) the so-called place-exchange reaction, (3) postsynthetic modifications, or (4) displacement of weak ligands (or protective agents) by functional ligands. 

We prepared boron substituted mordenite by direct synthesis from gel precursors and by post- synthetic substitution into dealuminated mordenite. Direct substitution is favored in aluminum deficient gels, but exacting crystallization requirements for mordenite formation limit the amount of boron that can be incorporated into the framework structure. Higher substitution levels were achieved using a post-synthetic treatment. Boron substituted zeolite Y could not be prepared by a similar direct synthetic method, but post-synthetic methods were effective at providing low substitution levels. This demonstrates the more general utility of post-synthetic substitution methods. The hexane cracking activity of... 

Thus it is proved that D-glucosamine is related configurationally to D-glucose. This same conclusion was reached independently by Cox and Jeffrey from x-ray analyses of a-o-glucosamine hydrochloride and hydro-bromide. The isomorphism of these substances enabled direct synthetic methods to be employed without any previous stereochemical assumptions and the atomic positions were determined with high precision. 

This synthesis involves a two-step reaction, the first of which yields an intermediate poly(amic acid) that is soluble in polar solvents. In the second, heating to temperatures of about 570 K elfects ring closure to form the insoluble, intractable polyimide. A more direct synthetic method, avoiding the ring closure step, makes use of diisocyanates. KAPTON has an extremely high heat distortion temperature of 630 K and shows exceptional thermo-oxidative resistance. 

We have developed a direct synthetic method for the one-pot synthesis of lactones, spirolactones, di-spirolactones, tertiary alcohols, and even 1,2-diols from the corresponding conjugated diene-magnesium reagents mediated by Rieke magnesium [122], The overall lactonization procedure can be considered... 

The discovery of the direct synthetic method for organosilicon compounds. (Rochow) [100]. 

Template-directed synthetic methods have been widely employed to create ordered mesoporous materials, in particular SiO and TiO. Mesoporous materials have unique features, for example, controllable pore size, high surface area, and regularly arranged channel systems [93]. 

From these reasons, the experimental fact that oxadiazole 28a (Figure 9.1) is formed as a result of cycloaddition of nitrile oxide 6 with aliphatic nitrile 29a even in the absence of activation is quite important. Namely, development of a direct synthetic method for 5-alkyl 1,2,4-oxadiazoles is expected to be possible, which is advantageous compared to other synthetic approaches to a 1,2,4-oxadiazole framework that require more extensive synthetic manipulations. It is considered that the higher reactivity of 6 for the cycloaddition with nonactivated common nitrile 29 arises from the diminished electron density as a result of the presence of a... 

CFa-attached heteroaromatics can easily be synthesized as well. Very importandy, trifluoromethylated alkenes, of which diere have been limited studies on the direct synthetic methods, can participate very well in the cross coupling, although a decrease of the yields can be observed and in addition the alkenes are partially isomerized during the reaction. 

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