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  • 1
    Electronic Resource
    Electronic Resource
    The Enantiomers of Spiro(cyclohexadiene-indolines) and their Thermal Racemization (1999)
    Springer
    Monatshefte für Chemie 130 (1999), S. 355-361 
    Details
    ISSN: 1434-4475
    Keywords: Keywords. Spiro(cyclohexadiene-indolines); Enantiomers; Enantioselective liquid chromatography; Thermal racemization.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung.  Die Enantiomeren von substituierten Spiro(cyclohexadien-indolinen) wurden durch enantioselektive Flüssigkeitschromatographie mit den Solvent/Sorbens-Systemen Triacetylcellulose/Methanol, Triacetylcellulose/Ethanol/Wasser und (+)-Poly(tritylmethacrylat)/SiO2/n-Hexan/Isopropanol getrennt. Aus thermischen Racemisierungen wurden die Barrieren der Enantiomerisierung für eine Reihe von Derivaten bestimmt. Ein Mechanismus der thermischen Ringöffnung und des Ringschlusses wird auf der Grundlage der Woodward-Hoffmann-Regeln diskutiert.
    Notes: Summary.  The separation of the enantiomers of substituted spiro(cyclohexadiene-indolines) was performed by enantioselective liquid chromatography with the sorbent/solvent systems triacetylcellulose/methanol, triacetylcellulose/ethanol/water, and (+)-poly(trityl methacrylate)/SiO2/n-hexane/isopropanol. The interconversion barriers of the enantiomers were determined for a series of derivatives by thermal racemization. A mechanism for the thermal ring opening/ring closure is discussed in terms of the Woodward-Hoffmann rules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010217
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  • 2
    Electronic Resource
    Electronic Resource
    Separation and Thermal Racemization of the Enantiomers of Spiro[cyclohexadiene-dihydroacridines] (2000)
    Springer
    Monatshefte für Chemie 131 (2000), S. 1083-1090 
    Details
    ISSN: 1434-4475
    Keywords: Keywords. Spiro[cyclohexadiene-dihydroacridines]; Enantiomers; Enantioselective liquid chromatography; Thermal racemization.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The enantiomers of substituted spiro[cyclohexadiene-dihydroacridines] were separated by enantioselective liquid chromatography with the sorbent/solvent systems triacetylcellulose/methanol, tris-(3,5-dimethylphenylcarbamoyl)-cellulose/silica gel (Chiralcel ODTM)/n-heptane/2-propanol, and (+)-poly-(trityl methacrylate)/silica gel/n-heptane/2-propanol. Interconversion barriers of the enantiomers were determined for a series of derivatives by thermal racemization. Electrocyclic ring opening/ring closure in terms of the Woodward-Hoffmann rules is discussed for the enantiomerization mechanism; the interconversion of the enantiomers by enolization is ruled out by deuterium exchange experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007060070041
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamic NMR study of the flexibility of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts (1997)
    Springer
    Fresenius' journal of analytical chemistry 357 (1997), S. 517-521 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dynamic NMR investigations of a number of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts were carried out. The barrier to rotation of the partial C, N double bond was determined and proved to be in the range of 62 to 63 kJ/mol. Quantum chemical calculations of bond orders and electron densities of the different atoms in the molecules show the distinct double bond character of the exocyclic C, N bond. This is in agreement with the relatively high barrier to rotation. By quantum chemical ab initio 3-21G calculations, the dynamic behaviour of this kind of compounds was simulated; two pairs (image and mirror image) of ground state conformations, in coincidence with the experiment, were obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160050205
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of two bacterial azoreductases acquired during adaptation to growth on azo dyes (1984)
    Springer
    Archives of microbiology 138 (1984), S. 37-43 
    Details
    ISSN: 1432-072X
    Keywords: Biodegradation ; Azo dyes ; Orange I ; Orange II ; Azoreductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Selection for utilization of carboxy-Orange I [1-(4′-carboxyphenylazo)-4-naphthol] in the chemostat yielded Pseudomonas strain K24 which was unable to grow on carboxy-Orange II [1-(4′-carboxyphenylazo)-2naphthol] while selection for growth on carboxy-Orange II had previously led to strain KF 46 which did not utilize carboxy-Orange I. Orange I azoreductase of strain K24, the key enzyme of dye degradation, was purified 80-fold with 17% yield to electrophoretic homogeneity and compared to the previously purified Orange II azoreductase of strain KF46. Common properties of the two enzymes were their monomeric structure, their specificity for NADPH and NADH as cosubstrates, the range of their K m values for substrates and cosubstrates as well as their reactivity towards a series of substrate analogs. They differed from each other with respect to molecular weight (21,000 and 30,000) and in the absolute requirement of Orange I azoreductase for a hydroxy group in the 4′ position of the naphthol ring of the substrate molecule as compared to the requirement for substrates with a 2-naphthol moiety by Orange II azoreductase. The pure enzymes did not exhibit immunological cross-reaction with each other. Crude extracts of strains K24 and KF46 and of azoreductase-negative strains isolated at different stages of the adaptation experiments, however, contained material which cross-reacted (CRM) with both anti Orange I azoreductase serum and anti Orange II azoreductase serum. The CRM may represent a common precursor protein of the azoreductases in strains K24 and KF46.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425404
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  • 5
    Electronic Resource
    Electronic Resource
    Agroforestry — a last hope for conservation in Haiti? (1986)
    Springer
    Agroforestry systems 4 (1986), S. 255-268 
    Details
    ISSN: 1572-9680
    Keywords: hillside cultivation ; erosion control ; maintenance of soil fertility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Haiti is the poorest country in the western hemisphere and one of the 25 poorest in the world. Its economy is marked by severe structural problems, and there is an extreme and widening gap between rich and poor. Per capita income in 1983 was US $315, and only about $50 in the countryside where many people live on the edge of starvation. Indices such as illiteracy, infant mortality and life expectancy are the worst in the hemisphere. Prolonged drought conditions since the mid-1970s have increased the country's external dependence, and much of the population depends on food aid. In the last few years several aid organizations have concentrated their efforts on reforestation programs with small farmers. Some programs are geared to production of fuelwood and timber as a source of cash income. Others propagate agroforestry as one possible solution to soil conservation and sustainable agriculture. Since 1983 the author has worked in Haiti as a technical consultant to local Caritas organizations working with many small groups of farmers engaged in agroforestry and soil conservation activities. The primary goal is to stop the process of hillside erosion, find new ways to prevent loss and degradation of agricultural land, make better use of rainwater, and promote self reliance in basic food crops.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02028360
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  • 6
    Electronic Resource
    Electronic Resource
    Pyryliumverbindungen. 33 [1] 2-Dialkylamino-2H-thiopyrane aus 2,4,6-Triaryl-thiopyryliumsalzen (1986)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 328 (1986), S. 567-572 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. 33. 2-Dialkylamino-2H-thiopyrans from 2,4,6-Triaryl-thiopyrylium Salts2,4,6-Triaryl-thiopyrylium salts 7 react with dialkylamines in diethyl ether to give stable crystalline 2-dialkylamino-2H-thiopyrans 8, the structure of which is in accordance with their u.v., n.m.r. and mass spectra. The chemical properties of 8 parallel those of structurally analogous 2-alkoxy- and 2-dialkylamino-2H-pyrans and 2-alkoxy-2H-thiopyrans. Thus, on heating 2-dimethylamino-2,4,6-triphenyl-2H-thiopyran (8a) with methanol the corresponding 2-methoxy-2H-thiopyran 9 is formed. Nitromethane and ethyl cyanoacetate give rise to ring transformations yielding 1,3,5-triphenyl benzene (10) and 2,4,6-benzonitrile (11), respectively. From 8a electrophiles (e.g. mineral acids, methyl iodide, benzoyl chloride) regenerate the initial thiopyrylium system by taking over the dialkylamino group.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19863280416
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  • 7
    Electronic Resource
    Electronic Resource
    Pyryliumverbindungen, XXVI. Vergleichende UV/Vis-spektroskopische Untersuchungen an 3-Methyl-2,4,6-triaryl-pyrylium-perchloraten (1985)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 327 (1985), S. 151-155 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXVI. Comparative U.V./Vis. Studies on 3-Methyl-2,4,6-triarylpyrylium Perchlorates
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19853270122
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  • 8
    Electronic Resource
    Electronic Resource
    Pyryliumverbindungen. XVIII, 2-Alkoxy-2H-pyrane aus tetra- und pentasubstituierten Pyryliumsalzen (1983)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 729-741 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XVIII. 2-Alkoxy-2H-pyrans from Tetra- and Pentasubstituted Pyrylium SaltsAlkali alkoxides add regioselectively to 2,3,4,6-tetrasubstituted pyrylium salts 7 (R'= H), affording high yields of colourless crystalline 2-alkoxy-2H-pyrans 9. The latte are also formed simply on refluxing 7 in the corresponding alcohol with triethylamine as proton acceptor. 3,5-Dialkylsubstituted 2,4,6-triarylpyrylium salts react analogously. The 2H-pyran structure of the adducts obtained follows from their n.m.r., i.r., u.v. and mass spectra as well as from their reaction with tetracyanoethylene to cycloadducts of type 10. Acids regenerate from 9 the original pyrylium cations, whereas reaction of 9 with nitromethane or ethyl cyanoacetate provides benzene derivatives. -- The novel starting pyrylium salts 7b--o are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19833250507
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  • 9
    Electronic Resource
    Electronic Resource
    Pyryliumverbindungen. 36. Substituierte Benzoesäureester aus 2,4,6-Triaryl-pyryliumsalzen und α-Ketocarbonsäureestern (1987)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 329 (1987), S. 499-510 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. 36. Substituted Benzoic Acid Esters from 2,4,6-Triarylpyrylium Salts and α-Ketocarboxylic Acid Esters2,4,6-Triarylpyrylium salts 1 react with α-ketocarboxylic acid esters 2 in the presence of two equivalents of an appropriate condensing agent (e.g. dialkylamine salts of weak acids, triethylamine/acetic acid, or sodium acetate) to give 2-aroyl-3,5-diarylbenzoic acid esters 3. However, using only one equivalent of the condensing agent, the formation of 3,5-diarylbenzoic acid esters 5 predominates. Alkaline saponification of the new esters 3 and 5 yields the corresponding substituted benzoic acids 4 and 6, respectively. - I.r., u.v., n.m.r. and mass spectroscopic data of the novel products 3-6 are reported.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19873290317
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  • 10
    Electronic Resource
    Electronic Resource
    Pyryliumverbindungen, XXV. Quantenchemische Berechnungen zur Valenzisomerisierung von 2-Amino-2H-pyran und -thiopyran (1984)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 955-961 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXV. Quantum Chemical Calculations Concerning the Valence Isomerization of 2-Amino-2H-pyran and -thiopyranThe equilibrium 2-amino-2H-pyran 6 ⇌ 5-amino-2,4-dien-1-one 7 was investigated using the semi-empirical MINDO/3 and MNDO methods. In accordance with experimental findings for the substituted derivatives 1/2a-d, the introduction of a methyl group into the position 3 of 6 or the exchange of oxygen by sulfur shifts the equilibrium towards the cyclic structures 8 and 10, respectively. Polar solvents, the influence of which was estimated applying the reaction field approach as well as the solvaton theory, and entropy effects are calculated to favour the ring-open valence isomer 7. These results also correspond to experimental results.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19843260614
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