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  • 1
    ISSN: 1434-193X
    Keywords: Indiumallyl compounds ; Vinylcyclopropanes ; α,β-Unsaturated carbonyl compounds ; Diastereoselectivity ; Dibenzylideneacetone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Allylindium reagents, prepared from excess allylic halide (Br or I) and indium metal, react with α,β-unsaturated ketones and aldehydes to give, after aerobic acidic workup, homoallyl-substituted vinylcyclopropanes. This process was explored and developed after a chance discovery arising from a side reaction in an attempted Pd-catalysed process. The structure of the cyclopropane arising from the reaction of bis(p-chlorobenzylidine)acetone was confirmed by X-ray crystallography. Whilst bis-α,β-unsaturated ketones give rise to a single homoallylcyclopropane species, α,β-unsaturated ketones and aldehydes give diastereomeric mixtures whose relative stereochemistry were assigned by NOE experiments. Crotylindium reagents react with good to perfect regioselectivity to afford tetrasubstituted cyclopropanes but prenylindium reagents fail to generate the analogous pentasubstituted rings.
    Additional Material: 5 Ill.
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  • 2
    ISSN: 1434-193X
    Keywords: Proton Sponges ; N-Chirality ; Isotopic labelling ; Stereodynamics ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,8-Bis(N-benzyl-N-methylamino)naphthalene (2) and its hydrogen iodide salt [2H]+[I]- were synthesised from 1,8-diaminonaphthalene. The thermodynamic diastereomer ratios of (2) and [2H]+ in [D7]DMF are 73.4:26.6 and 89.7:10.3 respectively at 293 K. The solid state structures of the major dl-(RNRNSNSN) diastereomers were determined by single crystal X-ray diffraction. The minor diastereomers were shown to be the meso-(RNSN) forms by performing 1H-NMR NOE studies on isotopically desymmetrized 1-(N-benzyl-N-[13C]-methylamino)-8-(N′-benzyl-N′-methylamino)naphthalene [13C]-2 and the salt [13C]-[2H]+. In [D7]DMF at 298 K, the meso form of the free base 2 is 0.6 (± 0.07) kcal·mol-1 less stable than the dl form (ΔH° = -0.64 (±0.03) kcal·mol-1; ΔS° = -0.18 (±0.13) cal·K-1mol-1) and the activation barriers for interconversion are ca. 14.2 (±0.4) and 14.8 (±0.4) kcal·mol-1 respectively. The effect of solvent polarity on the entropy and enthalpy change on approach to the transition state was studied. An approximate correlation with the solvent dielectric constant was found for both ΔH# and ΔS# and this may be ascribed to the development of a net dipole in the transition state due to substantially different hybridisation and geometry at the two nitrogen centres.
    Additional Material: 9 Ill.
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  • 3
    ISSN: 1572-9729
    Keywords: bacteria ; 2,5-dialkylthiphenes ; petroleum ; sulfate ; 2,5-thiophenedicarboxylic acid ; thiophenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract 2,5-Dialkylthiophenes are found in bitumens and crude oils, and previous studies showed that bacterial metabolism of some with a methyl substituent lead to the formation of 5-methyl-2-thiophenecarboxylic acid, which persisted in the culture medium (Fedorak PM & Peakman TM 1992 Biodegradation 2: 223–236). The objectives of this investigation were to study the further metabolism of this acid, and of two dialkylthiophenes, 2,5-diundecylthiophene and 2-(3,7-dimethyloctyl)-5-methylthiophene. Undefined, oil-degrading mixed cultures were used. 5-Methyl-2-thiophenecarboxylic acid was oxidized to 2,5-thiophenedicarboxylic acid which was identified by gas chromatography-mass spectrometry (GC-MS). This dicarboxylic acid was degraded and supported the growth of a mixed microbial population, and approximately 50% of the sulfur in this substrate was detected as sulfate in the medium at the end of the 15-day incubation time. Mixed cultures were incubated with 2,5-diundecylthiophene or 2-(3,7-dimethyloctyl)-5-methylthiophene as their sole carbon source, and at various times some of these were freezedried and the residues were treated to form methyl esters of any carboxylic acids produced. GC-MS analyses showed the presence of several dicarboxylic acids, indicating that both alkyl groups were oxidized. A small amount of the dimethyl ester of 2,5-thiophenedicarboxylic acid was detected in the culture grown on 2,5-diundecylthiophene, and 37% of the sulfur from this dialkylthiophene was detected as sulfate in the medium after 35 days of incubation.
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  • 4
    ISSN: 1572-9729
    Keywords: aerobic ; alkylthiophenes ; bacteria ; biodegradation ; isoprenoidal thiophenes ; petroleum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Six alkylthiophenes, 2-hexadecyl-5-methylthiophene (I), 2-methyl-5-tridecylthiophene (II) and 2-butyl-5-tridecylthiophene (III), 2-(3,7-dimethyloctyl)-5-methylthiophene (IV), 2-methyl-5-(3,7,11,15-tetramethyl-hexadecyl)thiophene (V) and 2-ethyl-5-(3,7,11,15-tetramethylhexadecyl)thiophene (VI) were synthesized and used as substrates in biodegradation studies. The products of their aerobic metabolism by pure bacterial cultures were identified. In most cases, the long alkyl chains of these thiophenes were preferentially attacked and in pure cultures of alkane-degrading bacteria, the major metabolites that accumulated in the medium were 5-methyl-2-thiopheneacetic acid from (I), 5-methyl-2-thiophenecarboxylic acid from (II) and occasionally from (V), 5-butyl-2-thiophenecarboxylic acid from (III) and 5-ethyl-2-thiopheneacetic acid from (VI). These transformations are consistent with the metabolism of the alkyl side chains via the beta-oxidation pathway. In contrast, 5-(3,7-dimethyloctyl)-2-thiophenecarboxylic acid was produced from (IV). Because it was available in greatest supply, (I) was studied most thoroughly. It supported growth of the six n-alkanedegrading bacteria tested and (I) was degraded more quickly than pristance but not as quickly as n-hexadecance in mixtures of these three compounds. In the presence of Prudhoe Bay crude oil and a mixed culture of petroleum-degrading bacteria, the acid metabolites from (I), (II) and (III) underwent further biotransformations to products that were not detected by the analytical methods used. The addition of n-hexadecane to the mixed culture of petroleum-degrading bacteria also enhanced the further biotransformations of the metabolites from (I).
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