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  • 1995-1999  (4)
  • 1985-1989
  • 1998  (4)
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  • 1995-1999  (4)
  • 1985-1989
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  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 945-953 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Simple methods are presented for handling, mounting, storage and transportation of crystals at cryogenic temperatures. They are easy to learn and have a number of technical and operational advantages over currently popular methods. In particular, the temperature of the crystal throughout all manipulations is known; it is shown never to rise above that of the warmest component of the cryogenic system, typically the cold gas stream of the low-temperature apparatus. Crystals can be mounted and inspected in the home laboratory prior to transportation to a synchrotron, giving dramatic savings in experimental time and effort. Provided appropriate care is taken, crystals remain frost free throughout any number of mount–dismount cycles.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 954-956 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The rates of cooling of small samples with cold N2 gas (100 K), liquid N2 (77 K) and liquid propane (100 K) have been measured. The samples were one bare Cu-constantan thermocouple and one coated with a 0.25 mm layer of silicone rubber cement. Gas cooling yielded the lowest rate, liquid N2 the highest. With the gas, cooling of the centers of the samples from 295 to 140 K took 0.8 and 2 s for the bare and coated samples, respectively; with liquid N2 the times were 0.15 and 0.6 s, and with liquid propane they were 0.15–0.18 and 1.2 s, respectively (time reproducibility is within ±10%).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In contrast to previously reported reactivity of the tungsten pentacarbonyl complex of a 2-substituted 1,2-dihydrophosphete, which apparently undergoes electrocyclic ring opening to the corresponding 1-phospha-1,3-butadiene and subsequent [4+2] cycloaddition reactions with dienophiles, the reaction chemistry of 1,3,4-triphenyl-1,2-dihydrophosphete is dominated by its nucleophilic nature. Although low to modest yields of cycloadducts are obtained with some dienophiles, the reactions forming these products are apparently stepwise, as indicated by the loss of stereochemistry in the reaction of dimethyl maleate and in the competitive formation of a phosphorus-free dimer in the reaction of N-methylmaleimide. Dimethyl acetylenedicarboxylate affords three major products, each of which incorporates two equivalents of the acetylene, again apparently a result of initial nucleophilic addition of the dihydrophosphete to the “dienophile.” © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:9-19, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilicity dominates the reaction chemistry of 1,3,4-triphenyl-1,2-dihydrophosphete even when it is coordinated to electrophilic metal centers, but coordination dramatically alters the course of its reactions. Deoxygenation of carbonyl-containing substrates is effected by both the W(CO)5 complex, which reductively couples benzaldehyde, and the HgCl2 complex, which converts benzaldehyde to α,α-dichlorotoluene. Metal coordination appears to decrease the tendency of the dihydrophosphete to undergo electrocyclic ring opening to the corresponding 1-phosphabutadiene, and the HgCl2 complex reacts with dimethyl acetylenedicarboxylate to afford a cyclopentadienyl ylide containing an intact dihydrophosphete unit. By reducing the nucleophilicity of the dihydrophosphete and/or the availability of the highly nucleophilic uncoordinated dihydrophosphete, coordination to HgCl2 and W(CO)5 makes accessible new mechanistic pathways. Dihydrooxaphosphinines, although unavailable through the reactions of the dihydrophosphete, may be synthesized by exploitation of the reactivity of organotitanium metallacycles. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:21-28, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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