Positioning capability

Although a large number of biscrown ethers based on the binaphthyl nucleus have been synthesized (157) many of these have only been isolated and characterized as their racemic modifications. An exception is provided (157) by (SS)-152, obtained from the chiral bisbinaphthyl-22-crown-6 derivative in which one of the binaphthyl units carries chloromethyl groups (in the 3 and 3 positions) capable of reacting, in the presence of base, with tetraethylene glycol. 

The precise positioning capabilities, which make high spatial resolution possible, give the SECM an important edge over other electrochemical techniques employing UMEs [20]. For example, the SECM can pattern the substrate surface, visualize its topography, and probe chemical reactivity on the micrometer or nanometer scale. Here, we briefly survey the fundamentals of various modes of the SECM operation and then focus on more recent advances in SECM theory and applications. 

Chemical synthesis of this ring system has been achieved by two basic methods. First, imidazoles with groups at the 4- and 5-positions capable of undergoing condensation to form the pyridazine ring have been employed. Second, 4,5-diaminopyridazines can be condensed with an appropriate one-carbon synthon to produce imidazo[4,5-<3Tlpyridazines. 

The relationship between the two classes of compounds is shown by the fact that the indamines may be easily converted into azines, and that monamines, with a free para position capable of yielding indamines on oxidation, give azines when the para positions are occupied. The conversion of-indamines into azines is especially instructive in the case of amidoindamines—for... 

The Michael addition of 6-aminouracils to dimethyl allene-l,3-dicarboxylate in methanol or dimethyl sulfoxide provides a pentenedioic acid side chain in the 5-position capable of further elaboration (Z-isomer in methanol, -isomer in dimethyl sulfoxide). Heating these adducts of 6-aminouracil or its 1-methyl derivative in dimethylformamide gives the corresponding pyri-do[2,3-d]pyrimidine-2,4,7(l//,3//,8//)-triones 7. 44... 

This is to say that the criteria for the machine tool to achieve ductile grinding of ceramics is accurate positioning capability and high repeatability to constantly control the grinding condition within [Pg.21]

Meta-cresol, which has three positions capable of methylolation, is high reactive with formaldehyde, and the alcohols formed resinify rapidly even under alkaline conditions. As a result, it is extremely difficult to isolate pure phenol alcohols. However, crystalline products beliei ed to be monoalcohols and melting at 105, 110, 117, and 122 C have been reported . The difficulties of isolating pure products are considerable, since three monomethylol derivatives, three dimethylol derivatives and one trimethylol derivative are possible. 

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