Near optics

In addition to the title procedure,10 other en2ymatic preparations of nearly optically pure (1R,4S)-(+)-4-hydroxy-2-cyclopentenyl acetate [(+)-1 ]s-11 and its optical antipode (-)-i 12,13.14,15.16 are known. These en2yme-catalyzed procedures are derivatives of two basic strategies (1) the enantioselective hydrolysis of the meso-diacetate 2,5.10 11 12 13 or (2) the enantioselective transacetylation of the parent meso-diol.14 15-16 Although (-)-1 has been successfully prepared by either route, the (+)-enantiomer is available only via the hydrolytic approach. 

The asymmetric hydrolysis of several cyclic meso-diesters has been accomplished and optically pure monoesters have been obtained. A classical example is the hydrolysis of dimethyl cis-4-cyclohexene-1,2-dicarboxylate, which affords the corresponding nearly optically pure half ester, a versatile synthon for various chiral cyclohexane derivatives (eq 3). ... 

The first catalytic asymmetric [2+2] cycloaddition reaction was reported in 1989 by the use of the chiral titanium reagent prepared from the tartrate-derived chiral 1,4-diol 1 and TiCl2(0-z-Pr)2 [26]. Treatment of methyl ( )-4-oxo-4-(2-oxo-l,3-oxazolidin-3-yl)-2-butenoate (2a) and l,l-bis(methylthio)ethylene (3a) with a 10 mol % amount of the chiral titanium reagent in a mixed-solvent of toluene and petroleum ether (RE.) at 0 °C afforded the cyclobutane derivative 4a in 96% yield in nearly optically pure form (98% ee) (Scheme 1). In this section we... 

Interestingly, dynamic kinetic resolution was observed for substrates with appropriate skeletal or functional perturbation. Such substrates are 3-oxo esters with amido-. carbamato- or ami-domethyl substituents at C-2 (Table 8). In the hydrogenation of these substrates with ruthenium-BIN AP catalysts, extremely high synianti ratios prevailed, with the major products of the L-threonine series being nearly optically pure60. 

A photomask is a nearly optically flat glass (transparent to near UV) or quartz plate (transparent to deep UV) with a metal absorber pattern printed on one side. The metal pattern is typically a 0.1 /zm thick chromium layer. The metal absorber pattern on a photomask is opaque to ultraviolet radiation, whereas glass... 

Kilaas R (1998) Optical and near-optical filters in high-resolution electron microscopy. J Microsc 190 45-51... 

Some properties of a PPX are summarized in Table 2.3. Parylene E, with 69% diethylated and 25% monoethylated p-xylylene groups shows unusual properties among the Parylene group. It is nearly optically isotropic. Therefore this Parylene type is a candidate for optical waveguides. It... 

They are sold under the tradenames of Lucite by E.I. duPont and Plexiglass by Rohm and Haas. Because of their chemical structure, acrylic resins are inherently resistant to discoloration and loss of light transmission. Parts molded from acrylic powders in their pure state may be clear and nearly optically perfect. The total light transmission is as high as 92%, and haze measurements average only 1%. 

Pedrazzoli (1957) catalytically reduced (VII) (Fig. 17) to unequal amounts of diastereomeric products which yielded nearly optically pure amino acids when hydrolyzed. Catalytic hydrogenation of the (—)-bornyl ester corresponding to (VII), however, yielded almost equal amounts of enantiomeric amino acids. Also, Yamada et al. (1962) hydrogenated (VIII) and obtained nearly... 

Some iron oxide-containing glasses are nearly optically transparent and can be used for heat-absorbing windows. Sulphatophosphate glasses when milled into plastics will act as fire retardants [29]. 

Substituted a,(3-unsaturated mono(sulfone) with other activating groups such as nitrile or ester were also applicable in the Michael addition with aldehydes. As reported by the group headed by Palomo [26], a-ethoxycarbonyl vinyl sulfones could react with aldehydes in the presence of 7 or 25 to give, after reduction and cyclization, the corresponding lactone adducts in nearly optical pure form with reasonable diastereoselectivity. Similar results were also obtained for a-cyano vinyl sulfones (Scheme 5.14). 

Although a scanned aperture can be used to write arbitrary patterns, the predominant use of photolithography is in replicating a pattern on a mask into a layer of photoresist. Such a mask, also called photo mask, is either a nearly optical flat glass, which is transparent to near UV or a quartz plate, transparent to deep UV covered with a metal absorber pattern (about 800 A thick chromium layer). Such a mask is either placed in physical contact with the resists (contact mode), or an image of the mask is reduced and projected into the resists with an optical system (projection mode). 

If the electrons are allowed to de-excite by falling back to the valence band, they will emit electromagnetic radiation. If this radiation is in, or near, optical wavelengths, it can be detected by a photomultiplier or other hght-measuring device to provide the detector signal. This is the basis of the scintillation detector. 

Near-optical-quality glass is generally required for both core and cladding glasses. Example combinations of refractive index combinations and the corresponding fiber characteristics are ... 

In a very similar manner, the combination of diethylaluminumcyanide and zinc chloride gives rise to the nearly optically pure cyanohydrin 486 [171]. 

Karrai, K., Grober, R. D. Piezoelectric tip-sample distance control for near optical microscopes. Appl Phys Lett 1995, 66,1842-1844. 

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