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  • Articles  (12,926)
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  • Kinetics
  • 1980-1984  (12,926)
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  • Articles  (12,926)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 260 (1982), S. 641-642 
    ISSN: 1435-1536
    Keywords: Kinetics ; Nucleation ; Water ; Emulsion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 262 (1984), S. 677-682 
    ISSN: 1435-1536
    Keywords: Kinetics ; methacrylamide ; reaction scheme ; viscosity ; additives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The aqueous polymerization of methacrylamide initiated by potassiumpersulfate-L-cystein hydrochloride redox system has been studied at 35±0.01
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  • 3
    ISSN: 1434-4475
    Keywords: Acetanilide ; Bromination ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the bromination of acetanilide has been studied with the diffusion layer titration method. The results have been obtained using the apparatus which consists of the ring-disc electrode and an amperostat-potentiostat system. Dependence of the ring current on the disc current has been determined as a function of rotation speeds of the electrode, of the solution concentration and temperature. It has been shown the bromination reaction of acetanilide exhibits by first order kinetics. In that case Br2 and Br3 − are the brominating species. The rate of bromination changes with the concentration of the Br− ions. This reaction rate depends on reactions of molecular bromine with acetanilide. For 0.033〈[Br−]〈0.173M the rate constant changes in the following range: $$17530M^{ - 1} s^{ - 1}〈 k〈 6400M^{ - 1} s^{ - 1} ([H + ] = 1,34;T = 298K)$$
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  • 4
    ISSN: 1434-4475
    Keywords: Kinetics ; Mechanism ; Mononitrosopiperazine ; N-Nitrosation ; Piperazine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Der Mechanismus der Bildung vonN-Nitroso-Verbindungen, die als potentielle carcinogene Substanzen gelten, wurde untersucht. Die Kinetik der Nitrosierung von Piperazin (PIP) in wäßriger Perchlorsäurelösung wurde mittels einer differentiellen spektrophotometrischen Methode verfolgt. Es ergab sich für denpH-Bereich 0,85–4,36 folgendes Zeitgesetz: $$v_0 = \left[ {nitrite} \right]_0 2 \left[ {PIP} \right]_0 /\left( {1 + f/\left[ {H^ + } \right]} \right)^2 \left( {g \left[ {PIP} \right]_0 + h + j\left[ {H^ \div } \right]} \right)$$ wobei [Nitrit]0 und [PIP]0 die anfänglichen stöchiometrischen Konzentrationen bedeuten. Bei 298,2 K und μ=1,0M,f=(1,17±0,11) 10−3 M,g=(3,5±0,7)·10−2 M s,h=2,6·10−6 M 2 s andj=(0,95±0,04)M s. Bei Erhöhung der Acidität ([HClO4]≥1M) tritt ein neuer kinetischer Term auf: $$v_0 ' = p\left[ {Nitrit} \right]_0 \left[ {PIP} \right]_0 $$ Bei 298,2 K und μ=3,0M,p=(1,9±0,2) 10−3 M −1 s−1. Es wird ein genereller Mechanismus für die Nitrosierung jedesN-nitrosierbaren Substrates in wäßriger Perchloratlösung vorgeschlagen, wobei als nitrosierende Agentien ausschließlich N2O3 und H2NO2 +/NO+ auftreten. Es werden die Besonderheiten dieses Mechanismus bezüglich derpK-Werte derN-nitrosierbaren Substrate diskutiert.
    Notes: Abstract The mechanism of formation ofN-nitroso compounds, which are considered as potential chemical carcinogens was studied. The kinetics of nitrosation of piperazine (PIP) in aqueous solution of perchloric acid have been investigated using a differential spectrophotometric technique. Based on our experimental results, the following rate law, in thepH-range 0.85 4.36, is proposed: $$v_0 = \left[ {nitrite} \right]_0 2 \left[ {PIP} \right]_0 /\left( {1 + f/\left[ {H^ + } \right]} \right)^2 \left( {g \left[ {PIP} \right]_0 + h + j\left[ {H^ \div } \right]} \right)$$ where [nitrite]0 and [PIP]0 represent initial stoichiometric concentrations. At 298.2K and μ=1.0M,f=(1.17±0.11) 10−3 M,g=(3.5±0.7) 10−2 M s,h=2.6×10−6 M 2 s andj=(0.95±0.04)M s. When the acidity is increased ([HClO4]≥1M), a new kinetic term comes into play: $$v_0 ' = p\left[ {nitrite} \right]_0 \left[ {PIP} \right]_0 $$ At 298.2 K and μ=3.0M,p=(1.9±0.2) 10−3 M −1 s−1. A general mechanism for the nitrosation of anyN-nitrosable substrate in aqueous perchloric solution in which the only nitrosating agents are N2O3 and H2NO2 +/NO+ is proposed. Also, the various particularities of this mechanism, according to thepK of theN-nitrosable substrate, are discussed.
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  • 5
    ISSN: 1434-4475
    Keywords: Galactitol ; Kinetics ; Mechanism ; Oxidation ; Reduction ; Xylitol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Das Geschwindigkeitsgesetz der Titelreaktion ist in beiden Fällen erster Ordnung bezüglich Hexacyanoferrat(III). Die Oxidation ist erster Ordnung bei niedrigen Konzentrationen von Xylit und Galaktit und geht bei Erhöhung der Konzentration gegen null. In gleicher Weise wurde eine Kinetik erster Ordnung bezüglich Hydroxyl bei niedrigen Konzentrationen und eine erniedrigte Ordnung bei höheren Konzentrationen für die Oxidation von Xylit beobachtet; bei Galaktit bleibt die Oxidation auch bei höheren Hydroxyl-Konzentrationen erster Ordnung. Es wird angenommen, daß die Reaktion über einen aktivierten Komplex zwischen [KFe(CN)6]2− und dem Substrat-Anion verläuft; dieser Komplex zerfällt in [KFe(CN)6]3− und ein Substrat-Radikal. Ein möglicher Reaktionsmechanismus wird vorgeschlagen.
    Notes: Abstract Kinetics of oxidation of xylitol and galactitol by hexacyanoferrate(III) ion in aqueous alkaline medium is reported. The reaction rate is of first order with respect to hexacyanoferrate(III) in each substrate. The reaction is first order at lower concentrations of xylitol and galactitol and tends towards zero order as the concentration increases. Similarly first order kinetics was obtained with respect to hydroxide ion at lower concentrations and tends to lower order at higher concentration in the oxidation of xylitol; in the oxidation of galactitol the reaction is first order with respect to hydroxide ion even up to manyfold variation. The course of reaction has been considered to proceed through the formation of an activated complex between [K Fe(CN)6]2− and substrate anion which decomposes slowly into radical and [K Fe(CN)6]3−. A probable reaction mechanism is proposed.
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  • 6
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    Springer
    Monatshefte für Chemie 112 (1981), S. 287-292 
    ISSN: 1434-4475
    Keywords: Activation energy ; Kinetics ; Methyl-vinyl ketone ; Polarography ; Polymerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The homogeneous polymerization of methyl-vinyl ketone in diluted methanol solutions in presence of proton donors is studied using the polarographic method. The effect of the cation of the indifferent electrolyte is investigated as well as the influence of small quantities of H2O. Suggestions were made about the possible mechanisms of these influences in the general scheme of the process proposed byHolleck et al.
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  • 7
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    Monatshefte für Chemie 113 (1982), S. 1087-1092 
    ISSN: 1434-4475
    Keywords: Dissolution ; Kinetics ; Pyrrhotite ; Rotating disc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Auflösungsgeschwindigkeit von natürlichem monoklinen Pyrrhotin, FeS1.14, wurde in sauerstofffreien LösungenS([H+]=0.1, [Na+]=0.9, [ClO 4 − ]=1.0 mol kg−1) mit Hilfe der Methode der rotierenden Scheibe bestimmt. Im Temperaturbereich von 40–90° erfolgt die Auflösungsreaktion kinetisch kontrolliert, wobei eine Aktivierungsenergie von 14±1 kcal mol−1 (59±5 kJ mol−1) gefunden wurde.
    Notes: Abstract Using the rotating disc method, the rates of dissolution of natural monoclinic pyrrhotite, FeS1.14, in oxygen-free aqueous solutionsS([H+]=0.1, [Na+]=0.9, [ClO 4 − ]=1.0 mol kg−1) were determined. In the temperature range 40–90 °C the dissolution reaction occurs under kinetic control; the activation energy being 14±1 kcal mol−1 (50±5 kJ mol−1).
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  • 8
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    Springer
    Monatshefte für Chemie 113 (1982), S. 1239-1244 
    ISSN: 1434-4475
    Keywords: Allyl alcohol ; Kinetics ; Mechanism ; Oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Kinetik der Oxidation von Allylalkohol mitN-Bromsuccinimid (NBS) wurde bei 35 °C in wäßrigem Medium untersucht. Die Reaktion zeigt erste Ordnung gegenüberNBS und Allylalkohol. Bei relativ hoher Säurekonzentration zeigt sich keine Änderung der Reaktionsgeschwindigkeit, bei niedriger Säurekonzentration wird die Reaktionsgeschwindigkeit beträchtlich erhöht. Es wurde kein primärer Salzeffekt festgestellt. Bei varriierender Quecksilberacetatkonzentration bleibt die Reaktionsgeschwindigkeit gleich, bei Abwesenheit von Quecksilberacetat wird jedoch die Geschwindigkeitskonstante erhöht. Die kinetischen Parameter,E a, derArrheniusfaktorA, ΔH ≠, ΔG ≠ und ΔS ≠ wurden bestimmt. Ein Geschwindigkeitsgesetz in Übereinstimmung mit den experimentellen Befunden wurde abgeleitet und ein Mechanismus vorgeschlagen.
    Notes: Abstract The kinetics of oxidation of allyl alcohol byN-bromosuccinimide (NBS) has been studied at 35 °C in aqueous medium. The reaction shows first order dependence on bothNBS and allyl alcohol. In fairly high acid concentration, there is no change in the rate of the reaction but at low acid concentration, the rate is considerably enhanced. There is no primary salt effect. At varying mercuric acetate concentrations, the rate constant remains the same. But in the absence of mercuric acetate, the rate is enhanced. The kinetic parameters,E a,Arrhenius factorA, ΔH≠, ΔG≠ and ΔS≠ have been calculated. A rate law in agreement with experimental results has been derived. A mechanism is proposed.
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  • 9
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    Monatshefte für Chemie 113 (1982), S. 887-893 
    ISSN: 1434-4475
    Keywords: Diazotation ; Kinetics ; α-Naphthylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Optimal diazotation conditions were determined by means of extinction measurements at various experimental conditions. The optimal conditions found arep H=9,5, the amount of phenol is 1 250 times the amount of α-naphthylamine.
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  • 10
    Electronic Resource
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    Monatshefte für Chemie 114 (1983), S. 773-781 
    ISSN: 1434-4475
    Keywords: Diastereomers ; 2,3-Dihydrobilatrienes-abc ; Kinetics ; Saturation-Transfer-Kinetics ; Phytochrome Models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract From kinetic and equilibrium measurements the activation and thermodynamic parameters of diastereomeric 2,3-dihydrobilatrienes-abc in positions “4” and “15” are deduced. Compared to bilatrienes-abc a pronounced thermal lability of these diastereomers is observed—the exocyclic double bond of the saturated lactam ring being the more labile one. This feature may be of relevance to the thermal cascades and dark reactions observed for phytochrome.
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  • 11
    ISSN: 1434-4475
    Keywords: Iodine monochloride ; Kinetics ; Solvent effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Kinetik der Addition von ICl zu einigen Vinylverbindungen in Nitrobenzol als Lösungsmittel wurde untersucht. In allen Fällen ist die Reaktion von zweiter Ordnung hinsichtlich ICl und von erster Ordnung hinsichtlich des Substrats, d. h. mit einer Gesamtordnung von drei. Geschwindigkeitskonstanten wurden für jedes Substrat bei 20°, 30°, 40° und 50°C gemessen. AusArrhenius-Diagrammen wurden Aktivierungsenergien ermittelt und auch andere kinetische und thermodynamische Parameter wurden bestimmt. Ein Mechanismus wird vorgeschlagen, wobei die verschiedenen Parameter diskutiert werden. Lösungsmitteleffekte werden ebenfalls diskutiert und die Daten mit Nitrobenzol und Essigsäure als Lösungsmittel miteinander verglichen.
    Notes: Abstract The kinetics of the addition of iodine monochloride (ICl) to some vinyl compounds in nitrobenzene solvent was investigated. In all cases the reaction follows second order dependence on ICl and first order on the substrate, making the total order three. Rate constants were measured for each substrate at 20°, 30°, 40° and 50°C.Arrhenius plots were made from which activation energies were evaluated. Other kinetic and thermodynamic parameters are reported. A suitable mechanism is proposed for the reaction and based on this, the various parameters are discussed. Solvent effects are discussed and the data with nitrobenzene and acetic acid solvents are compared.
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  • 12
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    Monatshefte für Chemie 115 (1984), S. 1185-1197 
    ISSN: 1434-4475
    Keywords: Mono and polycarboxylic esters ; Metal salt catalysis ; Kinetics ; Chromatographic analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The alcoholysis of various esters of aromatic carboxylic esters with octadecanol in the presence of lead stearate was investigated by chromatographic analysis of the reaction mixtures. The reactivity of the esters was found to be strongly affected by the substitution pattern of the aromatic nucleus as well as by the structure of the alkoxy group. Electron donating substituents in a suitable position lead to a remarkable increase in reactivity compared to the unsubstituted alkyl esters.
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  • 13
    ISSN: 1434-4475
    Keywords: Kinetics ; Negative salt effect ; Oxidation ; Stopped-flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of NaClO4, NaCl and Na2SO4 on the oxidation of Fe(phen) 3 2+ by Ce(IV) was investigated by means of the stopped-flow method. At the concentrations range of NaClO4 and NaCl 0.1–1.0M the rate constant values decrease from 1.03·105 to 0.56·105M−1s−1 and from 1.08·105 to 0.81·105M−1s−1 respectively. In varying concentrations of Na2SO4 solutions (0.05–0.35M) the rate constant values decrease from 1.05·105M−1s−1 to 0.45·105M−1s−1. Taking into account the negative salt effect the mechanism of the reaction progress is proposed.
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  • 14
    ISSN: 1434-4475
    Keywords: Arginine ; Catalysis ; Kinetics ; Mechanism ; Oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Oxidation erfolgt sowohl mit als auch ohne Cu(II)-Katalysator in erster Ordnung bezüglich des Oxidationsmittels und des Substrats; inverse Ordnung wird bezüglich der Alkalikonzentration beobachtet. Bis zu einer Cu(II)-Konzentration von≤2×10−5 M ist die Geschwindigkeitskonstante der Katalysatorkonzentration proportional; darüber wird eine konstantbleibende Geschwindigkeit beobachtet, die nun von der Cu(II)-Konzentration unabhängig ist. Neutralsalze haben keinen Effekt auf die Geschwindigkeitskonstante. Es wird für den katalysierten und unkatalysierten Reaktionsablauf ein Mechanismus vorgeschlagen und ein mathematischer Ansatz präsentiert.
    Notes: Abstract The kinetics of uncatalysed and Cu(II) catalysed oxidation of arginine monohydrochloride was investigated. Both reactions follow a singular order dependence each in oxidant and substrate. An inverse order dependence is reported with the alkali concentration. A plot of observed rate constant versus Cu(II) concentrations Cu(II)≤2.0×10−5 M is linear; from the intercept the rate constant for the uncatalysed pathway was calculated. However, at high copper ion concentrations i.e. Cu(II)〉2.0×10−5 M a fixed value of rate constant was found for all catalyst concentrations. Added neutral salts show an insignificant effect on the reaction rate. Mechanisms were proposed for both cases and rate expressions were derived by applying steady state assumptions.
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  • 15
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    Calcified tissue international 33 (1981), S. 431-439 
    ISSN: 1432-0827
    Keywords: Apatite ; Fluorhydroxyapatite ; Crystal growth ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The kinetics of seeded crystal growth of calcium apatites were studied in dilute supersaturated solutions at various levels of fluoride concentrations. Initial precipitation rates were enhanced by fluoride concentrations higher than 0.05 ppm. The analytical results are consistent with the precipitation of fluoridated hydroxyapatites, Ca5Fx-(OH)1−x(PO4)3, FHA. The degree of fluoridation, X, appears to be determined by the activity of HF in solution, which varies for the various initial fluoride levels but remains fairly constant during precipitation. Thus the composition of the precipitating phase was the same for a given solution whether 25 or 10 mg of hydroxyapatite was added as seeds. All the experimental results are consistent with the BCF theory, which relates the mean linear rate of growth, RL, to the supersaturation, DS, by the expression RL=C1T(DS-1)1n(DS)tanh(C2/T 1n DS), in which DS is the supersaturation defined by mean molar activities with respect to the precipitating FHA, T the absolute temperature, and C1 and C2 are constants calculated from the experimental results. Consequently, the crystal growth appears to take place in surface kinks and to be controlled by surface diffusion. Since crystal growth in most biological systems takes place at fluoride concentrations within the experimental range used, it seems probable that it occurs along the model advanced in the present investigation.
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  • 16
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    Monatshefte für Chemie 111 (1980), S. 1125-1133 
    ISSN: 1434-4475
    Keywords: Diazotization ; Kinetics ; α-Naphthylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the diazotization of α-naphthylamine1 in water HCl solution from 0,2N to 2.0N at 0 °C were investigated. It was found that the nitrosation reaction $$\alpha --C_{10} H_7 NH_2 + NOCl\mathop \rightleftharpoons \limits^{k_v } \alpha --C_{10} H_7 NH_2 NO^ + + Cl^ - $$ is a preceeding advance-back-reaction (velocity coefficient of the nitrosation is 1.92·1010l mol−1 s−1). The decomposition of I by splitting off a proton is the rate determining reaction. The free enthalpy of activation for the nitrosation reaction equals 12.94 kJ/mol.
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  • 17
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    Monatshefte für Chemie 111 (1980), S. 1135-1142 
    ISSN: 1434-4475
    Keywords: Hammet parameter ; Kinetics ; Mechanism ; Thermodynamic parameters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Kinetik der Reaktion von drei substituierten Acetophenonen mit Bromsuccinimid in Perchlorsäure in Gegenwart von Quecksilberacetat wurde untersucht. Die Reaktion war von nullter Ordnung gegenüberNBS, erster Ordnung gegenüber den Ketonen und [H+]. Mögliche Mechanismen der Reaktion werden diskutiert und auch eine Geschwindigkeitsgleichung wird abgeleitet. Es wurden die thermodynamischen Parameter der Reaktion bestimmt und auch einHammet'scher ϖ-Wert (+0,6) für die Oxidation der Methylarylketone ermittelt.
    Notes: Abstract The kinetics of the reaction of three substituted acetophenones withN-Bromosuccinimide was studied in perchloric acid media in presence of mercuric acetate. The reactions were found to be zero order with respect toNBS while the order with respect to ketones and [H+] was found to be unity. The addition of succinimide mercuric acetate and sodium perchlorate has no effect on the rate of oxidation and the rate increases with the decrease in dielectric constant of the medium. Kinetic investigations have revealed that the order of reactivity ism-nitroacetophenone 〉 p-chloroacetophenone 〉 p-methylacetophenone. TheArrhenius equation has been found to be valid in the temperature range 35–55°. Thermodynamic parameters have been calculated. Mechanistic pathways of the reactions are discussed and a rate equation is derived.Hammett's plot gives a ϖ value of +0.60 for methyl-aryl-ketones.
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  • 18
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    Monatshefte für Chemie 113 (1982), S. 3-14 
    ISSN: 1434-4475
    Keywords: Graphite ; Kinetics ; Reduction ; Thoria ; Thoriumcarbide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Reduktion von Thoriumoxid mit Graphit im Überschuß wurde mittels einer Thermowaage zwischen 1620 und 1920 K im Vakuum untersucht. Ab ThO2:C=1:50 war die Reaktionsgeschwindigkeit vom Mischungsverhältnis unabhängig; das Endprodukt war immer ThC2. Der logarithmische Gewichtsverlust war direkt proportional der Zeit, und dieArrheniusgerade zeigte einen Knickpunkt bei 1710 K: unterhalb dieser Temperatur ergab sich eine Aktivierungsenergie von 440 kJ, oberhalb eine solche von 260 kJ. Die Temperatur des Knickpunkts entspricht der Umwandlungstemperatur von monoklinem in tetragonal raumzentriertes ThC2.
    Notes: Abstract The reduction of thoria with excess graphite was studied with a thermo-balance in vacuum between 1620 and 1920 K. From Th02:C=1:50 the rate of reaction was independent of the ratio of the reactants; the endproduct was always ThC2. The logarithmic weight loss was directly proportional to the time, and theArrhenius plot showed a break at 1710 K: below this temperature the activation energy was found to be 440 kJ, above 260 kJ. The temperature corresponding to the break coincides with the transition temperature of monoclinic to body-centered tetragonal ThC2.
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  • 19
    ISSN: 1434-4475
    Keywords: Kinetics ; Ligand-transfer ; Thallium (III)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The transfer of oxinate ions from thallium (III)oxinate to trivalent Fe(DMF) 6 3+ in propylenecarbonate takes place via rearrangements within a rapidly formed binuclear thallium(III)—iron(III) complex. In a last rapid step this rearranged complex reacts with excess reactants to the final products whose composition accordingly depends on the ratio of the reactant concentrations.
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  • 20
    ISSN: 1434-4475
    Keywords: Hydroperoxide ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Bei der Zersetzung von α,α-Dimethylbenzylhydroperoxid (1) unter Verwendung eines Kupfer(II)chlorkomplexes wurde die neue Feststellung gemacht, daß das Produktverhältnis Acetophenon (2): α,α-Dimethylbenzylalkohol (3) stets 2:1 ist. Die Kinetik der Reaktion wurde untersucht und ein Mechanismus vorgeschlagen, der mit dem experimentellen Resultat konsistent ist.
    Notes: Abstract In the decomposition of α,α-dimethylbenzyl hydroperoxide (1) by use of copper(II) chlorocomplexes, the novel fact was found that the product ratio of acetophenone (2) to α,α-dimethylbenzyl alcohol (3) is 2 to 1. The kinetics of this result was investigated and a mechanism consistent with the experimental result is proposed.
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  • 21
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    Monatshefte für Chemie 114 (1983), S. 411-423 
    ISSN: 1434-4475
    Keywords: Bromination ; Dihydroxydiphenylmethanes ; Intramolecular hydrogen bonding ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The bromination of 15 dinuclear phenolic compounds (dihydroxydiphenylmethanes, methylene bisphenols) by molecular bromine in acetic acid was studied kinetically at 22°C. In all compounds the electrophilic substitution occurred inortho-position to the phenolic hydroxy group of the methyl phenol unit while the non reacting neighboring unit was differently substituted by H, CH3,t-Bu and NO2. A decrease in the reaction rate was observed in 2,2′-dihydroxydiphenylmethanes, where the +M-effect of the hydroxy group is diminished by an intramolecular hydrogen bond. The strength of this hydrogen bond may be influenced mainly by steric factors. Strong electron withdrawing substituents like NO2 show a rate decreasing influence on the reactivity of the neighboring unit also in 2,4′- and 4,4′-dihydroxydiphenylmethanes.
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  • 22
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    Monatshefte für Chemie 115 (1984), S. 1385-1392 
    ISSN: 1434-4475
    Keywords: Periodate oxidation ; Solvent effect ; Reaction rate ; Kinetics ; Octacyanomolybdate (IV)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Kinetik der Oxidation von Mo(CN) 8 4− mit IO4/− wurde in Ethanol—Wasser über einen Temperaturbereich von 15–35 °C untersucht. Der Effekt der Lösungsmittelzusammensetzung auf die Reaktionsgeschwindigkeit und der Mechanismus der Reaktion werden diskutiert. Die Aktivierungsparameter sind angeführt. Es wird ein „Inner-Sphere“-Mechanismus vorgeschlagen, der mit den kinetischen Ergebnissen konsistent ist.
    Notes: Abstract The kinetics of the oxidation of Mo(CN) 8 4− by IO 4 − has been studied in ethanol—water solvent mixtures over a temperature range of 15–35 °C. The effect of solvent composition on the reaction rate and the mechanism has been investigated. Activation parameters are given. An inner-sphere mechanism, consistent with the kinetic results, is proposed.
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    Monatshefte für Chemie 115 (1984), S. 405-414 
    ISSN: 1434-4475
    Keywords: Kinetics ; Mechanism ; Oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurde die Kinetik der Oxidation von Chinol mit Quecksilbernitrat in Gegenwart einer Mischung ausAcOH-H2O-HNO3 untersucht, um die aktive Species bei der Oxidation in diesem Medium aufzuklären. Die Reaktionsordnung ist sowohl bezüglich des Chinols als auch des Hg(II)-Ions erster Ordnung. Die Reaktionsgeschwindigkeit erhöht sich leicht mit der HNO3-Konzentration und auch mit abfallender Dielektrizitätskonstante des Mediums. Die Reaktionsgeschwindigkeit sinkt mit dem Zusatz von KNO3. Es ist keinerlei Hinweis auf eine Komplexbildung zwischen Chinol und Hg(II) festzustellen. Die Resultate der Untersuchungen legen HgNO + 3 als aktive Spezies nahe. Es wird ein möglicher Mechanismus mit einem Zweielektronen-Transfer im geschwindigkeitsbestimmenden Schritt vorgeschlagen. Das dabei produziertep-Benzochinon existiert nicht in freier Form, sondern es bildet einen stabilen 1 : 1-Komplex mit Quecksilbernitrat; dieser Komplex wurde mittels TLC und IR charakterisiert.
    Notes: Abstract The kinetics of oxidation of quinol by mercuric nitrate in presence ofAcOH-H2O-HNO3 mixture has been investigated in order to find the active species of mercuric nitrate involved in the oxidation in this medium. The order of reaction both with respect to quinol and Hg(II) is found to be one. The reaction rate slightly increases with the increase in [HNO3] and the decrease of the dielectric constant of the medium. The reaction rate retards on addition of KNO3. There is no evidence for complex formation between quinol and Hg(II). These results suggest that HgNO + 3 might be the active species in this medium. A probable mechanism involving a two electron transfer in the rate determining step has been suggested. The producedp-benzoquinone does not exist in free state but forms a stable (1 : 1) complex with mercuric nitrate which has been characterized by TLC and IR studies.
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    Monatshefte für Chemie 115 (1984), S. 697-704 
    ISSN: 1434-4475
    Keywords: Electrohydrodimerization ; Benzylidenemalononitriles ; Kinetics ; Electrohydrodimerization ; Benzylidenemalononitriles ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels derivativer cyclischer Voltammetrie wurden für die Titelreaktion Geschwindigkeitskonstanten und Aktivierungsparameter erhalten (Dimethylformamid als Lösungsmittel). Benzyliden-,p-Methyl- undp-Methoxybenzylidenmalonnitril reagieren ausschließlich über die Dimerisierung ihrer Anionenradikale (Radikal-Radikal-Kopplung), währenddessen die Dimerisierung vonp-Fluorbenzylidenmalonnitril zu 25% über die Kopplung des Anionenradikals mit dem Substrat erfolgt.
    Notes: Abstract Rate constants and activation parameters for the reductive dimerization of substituted benzylidenemalononitriles were obtained from derivate cyclic voltammetry measurements in dimethylformamide as solvent. Benzylidene-,p-methyl-andp-methoxybenzylidenemalononitrile react exclusively via dimerization of their anion radicals (radical-radical coupling) while forp-fluorobenzylidenemalononitrile 25% of the dimerization proceeds by coupling of the anion radical with the substrate.
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    Calcified tissue international 36 (1984), S. 48-59 
    ISSN: 1432-0827
    Keywords: Salivary proteins ; Adsorption ; Thermodynamics ; Kinetics ; Hydroxyapatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Equilibrium and kinetic experiments were conducted to investigate the factors determining the adsorption of salivary macromolecules onto hydroxyapatite. Using amino acids and other small adsorbates, it was determined that the carboxyl attached to the α carbon does not appear to adsorb onto HA and the affinities of side-chain carboxyls are much smaller than that of the phosphate group (phosphoserine). Hydroxyl (serine) displays an extremely high affinity, but its adsorption site on HA is different and the number of such sites is much smaller than found for the rest of the functional groups investigated. It is shown that the information obtained from small molecules cannot be readily applied to prediction of the adsorption behavior of salivary macromolecules and polypeptides. The kinetics of adsorption of the salivary phosphopeptide statherin, a polyaspartate, and the salivary prolinerich phosphoprotein PRP3 are consistent with the reversibility of the adsorption process; no conclusion was possible in the case of the protein PRP1. Apparent irreversibility cannot be explained on the basis of multipoint binding or the properties of the carboxyl versus phosphate group; it appears that secondary structure determines to a significant extent the adsorption properties of the macromolecules. Calculation of the thermodynamic molar quantities of adsorption of PRP1, PRP3, andl-ASP onto HA showed that the process is entropically driven. The functional relationship between partial molar entropy and adsorption coverage is similar for the two proteins, but quite different from that for aspartate. Explanations for these results are advanced on the bases of changes in structure configurations and displacement of water from the adsorbate and the adsorbent surface, the second factor being the dominant one in the adsorption of a small molecule such asl-ASP.
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    European biophysics journal 8 (1981), S. 23-34 
    ISSN: 1432-1017
    Keywords: Light-scattering ; Flash photometry ; Kinetics ; Visual transduction ; Biomembranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A recent development of kinetic light-scattering and -absorption photometry is described. Essential points are: 1) In the scattering experiment, amplitude resolution of 2 · 10−5 (single flash) by application of a differential detector, stability of the same magnitude due to optical compensation, high intensity at the detector due to special optics for the scattered light and semiconductor sources. 2) In the absorption measurement, elimination of scattering contributions by the dual wavelength-method and by high aperture optics. 3) Simultaneous measurement of absorption and scattering. The application of the method is described in using signals from isolated bovine rod outer segments. A reliable procedure is described by the use of which the originally measured light-scattering effects can be split up into single signals. The method allows comparative kinetic analysis of absorption and scattering signals. The possible causal connections between pigment and membrane structure processes can be selected.
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    European biophysics journal 9 (1983), S. 145-170 
    ISSN: 1432-1017
    Keywords: Viroids ; Thermodynamics ; Kinetics ; Hydrodynamics ; Function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Viroids are an independent class of plant pathogens which are distinguished from viruses by the absence of a protein coat and by their unusually small size. They are single-stranded circular RNAs composed of about 360 nucleotide residues. Sequence analysis and physicochemical studies of the potato spindle tuber viroid (PSTV) have shown that, as a result of intra-molecular base pairing, viroids form a unique rod-like secondary structure which is characterized by a serial arrangement of double-helical sections and internal loops. There is no indication for an additional tertiary structure because all parts of the molecule are freely accessible to ligand interaction. During the denaturation all of the native base pairs of viroids are dissociated in one highly cooperative transition, and in the same process very stable hairpins which are not present in the native structure are newly formed. Most of the properties of the structure and structural transitions of PSTV have been found also in citrus exocortis viroid, chrysanthemum stunt viroid and four different viroid-like RNAs associated with the cadang-cadang disease. The close similarity between these viroids is more expressed in the overall structure and in thermodynamic and functional domains than in the primary sequence. The stiffness of all viroids can be described by an unique persistence length of 300 å. Characteristically, regions of premelting, regions of stable hairpins, and the sequence UACUACCCGGUGG which is opposite to one of the stable hairpins, are the most conservative sequences in the molecules. Current hypotheses about the function of viroids are discussed on the basis of their structural and thermodynamic features. The suggestion that viroid RNA has features similar to DNA has been supported by the finding that they are replicated in vitro by the DNA-dependent RNA polymerase II of the host plant. The highly conserved sequence in viroids mentioned above corresponds very closely to a segment at the 5′-end of the small nuclear RNA U1 of eukaryotes. Because this segment is discussed in recent models, to be involved in the splicing process, a hypothesis is proposed in which viroids interfere with the splicing process leading to a pathogenic misregulation of mRNA processing.
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    Archives of microbiology 139 (1984), S. 28-32 
    ISSN: 1432-072X
    Keywords: Cyanobacterium ; Phosphate ; Uptake ; Kinetics ; Regulation ; Pulse ; Steady state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to study phosphate uptake kinetics the cyanobacteriumOscillatoria agardhii was grown in continuous culture under a phosphorus limitation. The affinity of the uptake system reflected in the initial slope of the uptake rate versus external substrate concentration curve (dV/ds) was found to be unaffected by the growth wate. The maximum phosphate uptake rate (V m ) decreased as the growth rate was increased. Attempts were made to relate the decrease ofV m to the increase in phosphorus content of the cells that occurred a higher growth rates. Accumulation of phosphate during pulse experiments indeed resulted in a decrease ofV m . However feedback regulation ofV m by accumulated phosphorus was found to occur only to a small extent in steady state growing cells. The main part of the regulation of the activity of the phosphate uptake system seemingly is determined by a long term process that is, at least longer than 2 h. The presence of short term feedback inhibition by accumulated phosphorus on the activity of the uptake system provides an explanation of the phenomenon thatOscillatoria agardhii is not able to grow at nearμ max growth rates under a phosphorus limitation.
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    Plant and soil 54 (1980), S. 359-381 
    ISSN: 1573-5036
    Keywords: Alaska ; Ammonium ; Birch ; Forest-floor ; Isotopedilution ; Kinetics ; Nitrate ; Nitrogen pool
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary An analysis was conducted of nitrogen dynamics in the forest floor of a paper birch forest in subarctic Alaska. Low addition levels of high enrichment isotope (〈1% of the total nitrogen pool with 95 to 99 atom percent excess15N) and isotope dilution analysis, were used to establish the kinetics of nitrogen flow. The pools examined were NH4, NO3+NO2, soluble organic-N and forest floor organic matter. This approach allows a more realistic assessment of rates of N movement at the levels of nitrogen concentration encountered in natural systems.
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    Plant and soil 54 (1980), S. 399-417 
    ISSN: 1573-5036
    Keywords: Adsorption ; Anodic stripping voltammetry (ASV) ; Kinetics ; Lead ; River-mud
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The effects of several factors on the rate and the capacity of lead adsorption by river-mud were studies. These factors included the concentration of mud, the concentration of lead, the organic matter content of mud, pH, time of adsorption, temperature and agitation. The reaction order of the adsorption process with respect to lead and the type of adsorption were determined. Also, indications of the rate-limiting step were discussed and an empirical equation describing the adsorption of lead on river-mud was developed.
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    ISSN: 1573-5036
    Keywords: Ammonification ; Cadmium ; Heavy metals ; Kinetics ; Lead ; Nitrification ; Perfusion incubations ; Polluted soils ; Selection ; Toxicity ; Zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The sensitivity of the mineralization of nitrogen by a range of soils contaminated with heavy metals (up to 340 μg Cd g−1, 7500 μg Pb g−1 and 34000 μg Zn g−1) to the addition of heavy metals in solution were studied using pot incubations (ammonification) and a soil perfusion technique (nitrification). The ammonification of peptone showed little correlation between treatments with Cd, Zn (1000 and 5000 μg g−1) and Pb (10000 and 20000 μg g−1) and origin of the soil. Nitrification was considerably more sensitive to heavy metals than ammonification. All the soils had active, often large, populations of ammonifying and nitrifying organisms which showed substantial similarities between the soils. The rate of nitrifying activity (NO3−N production) was logrithmic in most cases. The presence of tolerant populations of nitrifying organisms in the contaminated soils was demonstrated. Tolerance was also eventually acquired after a longer lag phase, by the non-contaminated soil populations although the rate of activity was often reduced. Metals added in solution were adsorbed by the soil within 4 hours. Differences in toxicity between metal salts (chlorides, sulphates and acetate) were attributed to the amount left in solution. However, in many instances, acetate was found to stimulate all the stages in the mineralisation of nitrogen.
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    Journal of statistical physics 30 (1983), S. 219-241 
    ISSN: 1572-9613
    Keywords: Kinetics ; phase transitions ; nucleation ; lattice gas ; Becker-Doring equations ; clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method is described for calculating from first principles the coefficients in the Becker-Döring equations for the rate of change of the distribution of cluster sizes in a low-density lattice gas with Kawasaki dynamics. The method depends on solving a diffusion problem for the concentration of particles near a given cluster. The coefficients are calculated for cluster sizes up to 6, on a simple cubic lattice at a temperature 0.59 times the critical temperatures, and extrapolated to larger sizes. The resulting version of the Becker-Doring equations is then solved numerically. Comparison with the results of a computer simulation (at overall concentration 0.075) carried out by Kalos and others indicates that the method gives quite good predictions of the dependence of the cluster distribution on the critical cluster size (usually denoted by l*) but that the predicted rate of change of critical cluster size with time is too small, at this overall concentration, by a factor of about 0.3.
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    Journal of statistical physics 34 (1984), S. 399-426 
    ISSN: 1572-9613
    Keywords: Kinetics ; Becker-Doring equations ; clusters ; computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We make a quantitative comparison between the predictions of the Becker-Döring equations and computer simulations on a model of a quenched binary A-B alloy. The atoms are confined to the vertices of a simple cubic lattice, interact through attractive nearest neighbor interactions, and move by interchanges of nearest neighbor pairs (Kawasaki dynamics). We study in particular the time evolution of the number of clusters of A atoms of each size, at four different concentrations: ρA=0.035, 0.05, 0.075, and 0.1 atoms per lattice site. The temperature is 0.59 times the critical temperature. At this temperature the equilibrium concentration of A atoms in the B-rich phase is ρ A eq =0.0145 atoms/lattice site. The coefficients entering the Becker-Döring equations are obtained by extrapolation from previously published low-density calculations, leaving the time scale as the only adjustable parameter. We find good agreement at the three lower densities. At 10% density the agreement is, as might be expected, less satisfactory but still fairly good-indicating a quite wide range of utility for the Becker-Döring equations.
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    Helvetica Chimica Acta 63 (1980), S. 658-663 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New Routes to 1H- and 2H-PyrrolesA synthesis of 1H-pyrroles is described starting with pyridine analogues of chalcones and involving the reaction of acetic anhydride with 1-pyrroline-1-oxides. Another route leads from 1-pyrrolines to 2 H-pyrroles via bromination with N-bromosuccinimide and subsequent dehydrobromination in dimethylformamide.
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    Helvetica Chimica Acta 63 (1980), S. 681-681 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
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  • 36
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compound 1 is a further example of an olefinic alcohol that undergoes ether formation under basic conditions (→ 3) although the double bond is not activated by an electron-attracting group. This unusual reactivity is due to steric compression, which is increased in the 10-methyl analogue 2. This forms the corresponding ether 7 at a much higher rate. - In a deuteriated medium, base-catalysed cyclization of 1 gives the exo-deuteriated ether 6, corresponding to trans-addition. - An X-ray structure analysis of 4, the p-nitrobenzoate of 1, is presented.
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: A substitute for the Darzens glycidic ester synthesis for converting unsaturated ketones or aldehydes into the homologated β,γ- or α,β-unsaturated aldehydes employing sulfur ylides is described. The carbonyl group is converted into the unsaturated oxirane which is then rearranged to the new aldehyde. High yields of isomerically pure aldehydes are available by this method and the process is of practical importance in the conversion of β-ionone into the β-C14-aldehyde, a key intermediate in the Isler synthesis of vitamin A. The efficient preparation of α- and β-cyclocitral by the novel process is also described.
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  • 38
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Six iridoid glucosides have been isolated from Globularia cordifolia by the combination of open column - and high performance liquid chromatography. The structure of the new compound, named globularifolin, and the identity of the others have been established by chemical transformations and spectral evidence of the compounds and their derivatives.
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    Helvetica Chimica Acta 63 (1980), S. 132-147 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of selected tetramethylpiperidine derivatives with radicals arising from the Norrish-type I cleavage of dibenzyl ketone under oxygen was studied. Product analyses and kinetic studies showed that the investigated sterically hindered piperidine derivatives have a pronounced effect on both the nature and distribution of the products of photolysis of dibenzyl ketone in the presence of oxygen. Observations indicated that the phenylperacetoxyl radical is formed as an intermediate during irradiation and that it interacts with the additives used. Possible mechanisms of the reactions studied are discussed.The observation that oxidation of an isolated double bond by the radicals formed in dibenzyl ketone photolysis under oxygen is strongly inhibited in the presence of the studied sterically hindered amines is discussed in the light of the results presented. The findings are considered in relation to the problem of polymer stabilization.
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  • 40
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several attempts to prepare 3-acetyl-5-benzyl-3-pyrrolin-2-one (7) from phenylalanine are described. This goal was only reached formally, because compound 7 exists in the tautomeric form of (Z)-5-benzyl-3-(1′-hydroxyethylidene)-4-pyrrolin-2-one (17) according to the spectral data. The problem of tautomerism in pyrrolinone systems is discussed.
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    Helvetica Chimica Acta 63 (1980), S. 102-116 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic Aminoalkylation with ThiopivalamidesVorläufige Mitt. [1].Of the twelve thioamides 7a-e and 8a-g, only N,N-dimethylthiopivalamide (7a) could be metallated at the CH-group in a-position to the N-Atom. The reagent 9 thus obtained (Table 1) reacts in high yields with primary haloalkanes, with aldehydes, and with non-enolizable ketones (Table 2). As shown in Scheme 1, the products can be hydrolyzed to pivalamides, cleaved to secondary amines, or reduced to neopentylamines (see 18/19, 15/equation (4) and (5), and 16/20, respectively).
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    Helvetica Chimica Acta 63 (1980), S. 1920-1925 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Excitation spectra of the cations of pentafluorophenol, 2,3,4-trifluorophenol, 2,4,5-trifluorophenol, 2,5-difluorophenol and 3,5-difluorophenol have been obtained by pumping the B̃2 A″ ← X̃2A″ transition with a dye laser. The cations were first produced in their ground states by Penning ionisation using argon metastables. Vibrational frequencies of some of the fundamentals have been inferred for these cations in the B̃2 A″ state from the excitation spectra, and in the X̃2 A″ state from the emission spectra. Possible applications of the reported results are suggested.
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  • 43
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Polyhalogenated Butyryl Chlorides, Precursors of Pyrethroid HaloketenesThe copper (I)-catalyzed free radical addition of halomethanes to acrylates and the addition of halogenated acetic acid derivatives to fluoro- or chloro-substituted ethylenes affords polyhalogenated butyric acid derivatives. Chlorides of these acids serve as precursors for haloketenes used in efficient syntheses of pyrethroids.
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    Helvetica Chimica Acta 63 (1980), S. 2010-2014 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: The pyrrolidines 2 and 10 were obtained by thermal ene-reactions at +70° and +180° from the (Z)-4-aza-1, 6-diene 1 and from the (E)-4-aza-1, 6-diene 9 in the ratios of 75:25 and 50:50, respectively. On the other hand, these cyclizations proceeded readily in the presence of diethylaluminum chloride at - 78° and - 35° giving in high yield the trans-pyrrolidine 2 from 1 with 100% and from 9 with 89% diastereoselectivity.
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  • 45
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Low Temperature 13C-NMR. Spectra of 13C- and 6Li-Labelled Chloro-, Bromo-, and Iodo-lithiumcarbenoidsThe 13C-NMR. spectra of tetrahydrofuran solutions of 16 chloro-, bromo-, and iodo-6lithio- and -7lithio-carbenoids with 13C-labelled methane, ethane, ethylene, and cyclopropane C-skeletons have been measured at temperatures around - 100° (for examples see Fig. 1 and 2). Invariably, the exchange of hydrogen or halogen by lithium causes deshielding (Δδ, see Table 1) of the 13C-signal by up to 289 and 434 ppm, respectively, and decrease of 1J (1H, 13C) and 1J(13C,13C) couplings (see Table 2) with the C-atom of up to 104 and 30 Hz, respectively. The 1J(6Li, 13C) and 1J(7Li, 13C) coupling of ca. 17 and 45 Hz, respectively, obtained in ten cases (Table 1) is independant of the substitution pattern of the C-skeleton and of the particular halogen atom.
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: 1H- and 13C-NMR. data are reported for the complexes [Pt(1)L] and [Pt(2)L]; 1 = OC6H4CH = NCH2CH2O, 2 = OC6H4CH = NC6H4O; L = PR3, AsR3, C ≡ N (cyclohexyl), DMSO, pyridine, secondary amine. The molecular structures of [Pt (2) (NHEt2)] (I) and [Pt (2) (PPh3)] (II) have been determined by X-ray analysis. Relevant bond distances for I: Pt-N (amine) = 2.076 Å, Pt-N (imine) = 2.017 Å, Pt-O = 1.992 Å and 2.002 Å; for II: Pt-P = 2.248 Å, Pt-N = 2.064 Å, Pt-O = 1.964 and 2.005 Å. Both the solid and solution state data are interpreted in terms of differences in the trans influence of the ligand L. The question of metal-ligand d-p π back bonding to the imine is discussed.
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: The complexation of primary ammonium salt substrates by macrocyclic polyether receptor molecules provides a general method for studying the nature and stereochemistry of intermolecular interactions. The substrates and receptors are fitted each with one of the interacting units and the resulting effects in the complex are analyzed. The method is used to study the biologically important indole-pyridinium donor-acceptor interaction. The complexes between macrocycles, bearing an indole group in side chains, and pyridinium-ammonium salts display a characteristic charge-transfer band. The absorption coefficients and stability constants have been determined. Competition experiments also provide a new method for measuring the stability constants of macrocycle-ammonium complexes in organic solvents.
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aristoserratine, a New Indole Alkaloid from Aristotelia serrata W.R.B. OLIVER and from A. peduncularis (LABILL.) HOOK. F.The new indole alkaloid aristoserratine (2) has been isolated from Aristotelia. Its structure and absolute configuration were elucidated on the basis of spectroscopic data.
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  • 49
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    Helvetica Chimica Acta 63 (1980), S. 2152-2158 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When the Hammett-Taft equation log (k/ko)=ρq · σ1q is applied to the solvolysis of the 3-substituted propyl bromides 6a-6i in ethanol/water 4:1 (v/v) log k correlates linearly with σ1q except in cases where R exerts an anchimeric effect. The reaction constant ρq for 6 is - 0.12 and is typical for a nucleophilic solvent-assisted ks process at a primary C-atom. The tertiary halides 1 and 3, however, which react with little or no nucleophilic solvent assistance, i.e. by kc processes, lead to larger ρq values of -0.71 and -1.14, respectively. The reaction constant pq is therefore a sensitive gauge for charge development in the transition state for solvolysis of saturated compounds.
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  • 50
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of Some 3-Deoxy-3-trifluoroacetamido-D-ribofuranosyl Halides with Mercuric CyanideThe expected 2,5-anhydro-D-allononitrile 11 was obtained when the 2-O-benzoyl-3-deoxy-3-trifluoroacetamido-D-ribofuranosyl bromide reacted with mercuric cyanide, whereas the isomeric 1,2-O (1-cyanoethylidene) derivative was formed from the 2-O-acetylated halide; no reaction occurred when the halide was 2-O-p-nitrobenzoylated.
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  • 51
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    Helvetica Chimica Acta 63 (1980), S. 2264-2270 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of electrically neutral lipophilic di-, tri-, and tetra-amides containing tertiary-amine N-atoms were prepared in order to investigate their selectivity for alkali and alkaline earth metal cations in solvent polymeric membranes. Considerable selectivity changes were observed for membranes incorporating certain of these ligands as compared with ligand-free membranes. A 1:1 cation/ligand complex was isolated from N, N′, N″-triheptyl-N, N′, N″-trimethyl-nitrilotriacetamid and Mg (SCN)2 whereas with Ca (SCN)2 the corresponding 2:3 cation/ligand complex was formed. N, N′, N″, N‴, N‴-tetramethyl-ethylenediaminetetraacetamide yields a 1:1 cation/ligand complex with Mg (SCN)2.
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  • 52
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Contribution to the Mass Spectral retro-Diels-Alder Reaction: 1,2,3,4-Tetrahydrophenanthrene[1,4-13C]-1,2,3,4-Tetrahydrophenanthrene (1) was synthesized starting from [1,4-13C]-succinic acid. The mass spectral behavior (EI./MS., 70eV) of 1 is very similar to that of tetraline [2] concerning its loss of ethylene from the molecular ion. Similarly the fragmentation reaction of the synthetic precursors, ketones 7 and 8, seems to partly undergo a carbon rearrangement reaction prior to the elimination of ethylene which is unlike to the behavior of α-tetralone.
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  • 53
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Contributions to the Knowledge of the Corrin Chromophore, X. Reaction of Derivatives of Cobyrinic Acid Heptamethyl Ester with Hypochlorous Acid(Cobalt)-dicyano-, chloro-cyano-, and dichloro-cobyrinic acid heptamethylesters (1, 2 and 3), respectively, as well as their 10-chloro derivatives 4, 5 and 6 react with hypochlorous acid. A report on the structure and some properties of the reaction products 8, 9 and 10 is given.
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  • 54
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    Helvetica Chimica Acta 63 (1980), S. 2342-2357 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3β, 19-Epoxy-3 α-methoxy-steroids (e.g. 1, Scheme 1) are converted into the corresponding 3 α-methoxy-19-oxo compounds (e.g. 3) in the presence of boron trifluoride etherate, via an intramolecular hydride ion transfer from C (19) to (3) which is shown to be an equilibrium process. By subjecting the specifically deuteriated (19 S)- and (19 R)-compounds 1b and 1c to this reaction it was shown to be highly stereoselective.
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  • 55
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    Helvetica Chimica Acta 63 (1980), S. 2375-2379 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemically and isotopically pure Al35Cl3 and Al37Cl3 are synthesized from Al (s) and HCl (g). The yield is quantitative and no measurable decrease in isotopic content from HCl to AlCl3 takes place.
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  • 56
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The UV. irradiation of 17 β-acetoxy-4-oxa-5 α-androst-1-en-3-one (1) yields A,B-diseco-steroids originating from a Norrish I process of the lactone function.
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  • 57
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural Dynamics of Pentadienyl Metal-Compounds Bearing a Terminal Alkyl Substituent: Both ‘Stereoselective’ and ‘Stereodefensive’ Synthesis of a Natural Perfume.The (2Z, 4E)-, (2E, 4Z)- and (2E, 4E)-isomers of 2,4-decadien-1-ol (5) have been obtained with high and predictable stereochemical homogeneity starting from both (Z)- and (E)-1, 4-decadiene. These hydrocarbons were hydroxylated in a reaction sequence consisting of metallation (by means of s-butyllithium or butyllithium/potassium-t-butoxide, giving rise to organometallic intermediates of specific conformation), dimethoxyborylation and oxidation. The different decadienols as well as (2E, 4Z)-2, 4-undecadien-1-ol were converted into the isovalerates, the ester derived from (2E, 4Z)-2, 4-decadien-1-ol being a natural flavor component.
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  • 58
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Chemical transformation of tricyclo [3.3.0.02,8]octan-3-one (1) have been carried out in order to explore its potential utility as a versatile synthon for polycyclopentanoid terpenes and prostacyclin analogs. Various functionalizations of rings A and B and annulation of a third ring C were achieved in generally high yields. The system provides for a large measure of regio- and stereoselective reaction control.
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  • 59
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Replacement of lithium or magnesium by titanium can furnish nucleophilic organometallic reagents of high selectivity as exemplified by the title compound 1 (see Tables 1-3).
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  • 60
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleosides and Nucleotide. Part 15. Synthesis of Deoxyribonucleoside Monophosphates and Triphosphates with 2(1H)-Pyrimidinone, 2(1H)-Pyridinone and 4-Amino-2(1H)-pyridinone as the BasesThe phosphorylation of the modified nucleosides 1-(2′-deoxy-β-D-ribofuranosyl)-2(1 H)-pyrimidinone (Md, 4), 4-amino-1-(2′-deoxy-β-D-ribofuranosyl)-2(1 H)-pyridinone (Zd, 6) and the synthesis of 1-2′-deoxy-β-D-ribofuranosyl-2(1 H)-pyrimidinone-5′-O-triphosphate (pppMd, 1), 1-(2′-deoxy-β-Dribofuranosyl)-2(1 H)-pyridinone-5′-O-triphosphate (pppIId, 2), and 4-amino-1-(2′-deoxy-βD-ribofuranosyl)-2(1 H)-pyridinone-5′-O-triphosphate (pppZd, 3) are described. The nucleoside-5′-monophosphates pMd (5) and pZd (7) were obtained by selective phosphorylation of Md (4) and Zd (6), respectively, using phosphorylchloride in triethyl phosphate or in acetonitril. The reaction of pMd (5) pII d (8) or pZd (7) with morpholine in the presence of DCC led to the phosphoric amides 9, 10 and 11, respectively, which were converted with tributylammonium pyrophosphate in dried dimethylsulfoxide to the nucleoside-5′triphosphates 1, 2 and 3, respectively.
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  • 61
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two novel cannabinoid model compounds, (3R, 4R)-Δ1(6)-tetrahydrocannabinol-5″-oic acid (22) and 4″(R, S)-methyl-(3R, 4R)-Δ1(6)-tetrahydrocannabinol-5″-oic acid (23) were synthesized by acid-catalyzed condensation of (+)-trans-p-mentha-2, 8-dien-l-ol (1) with the substituted resorcinols 18 and 19 obtained by a Wittig reaction between 3, 5-bis(benzyloxy)benzaldehyde (7) and methyl 4-bromobutanoate (10) or methyl 4-bromo-2(R, S)-methylbutanoate (11) resp. with subsequent hydrogenation. The resulting methyl esters 20 and 21 were hydrolyzed to give acids 22 and 23.
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  • 62
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    Helvetica Chimica Acta 63 (1980), S. 2538-2553 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In HSO3F/SO2ClF the β-hydroxy esters Ph-CHOH-CMe2-COOR (1, R=Me, Et) are doubly protonated, then transformed into the fluorosulfates 7 and (partly) into the fluorides 8. At -15°, both 7 and 8 undergo a rearrangement, forming derivatives of Me2C=C(Ph)COOR (2). By labelling 1 with 13C, singly (13C(3)) and doubly (13C(1,3)), it could be shown that exclusively the ROOC groups undergo a 1,2-shift. Compound 2 is also formed in HSO3F/SO2ClF from the isomeric Me2COH-CHPh-COOR (3) by elimination, and less easily from the α-hydroxy ester Ph-CMe2-CHOH-COOR (5) via a phenyl 1,2-shift. Another isomer, Ph-C(OH)Me-CHMe-COOR (4) gives products different from 2.Using more acidic systems containing SbF5, the free carbenium ions 13 (Ph-CH+-CMe2-COOR) can be stabilized; they do not form 2, possibly because of complexation of the ester group with SbF5. The energy profile and the mechanism of the rearrangement 1 → 2 are discussed.
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  • 63
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that ligand 1, designed to span trans-positions, under appropriate conditions also gives cis-mononuclear complexes of platinum (II). The structure of cis-[PtCl2 (1)] (2) has been determined by single-crystal X-ray diffraction. The major distortion from square planar coordination is the P-Pt-P angle of 104.8°. Values of valence angles within the bidentate ligand indicate that this part of the molecule is very strained. Two phenyl groups, one on each phosphorus, lie almost parallel to each other separated by ca. 3.2-3.3 Å. The 1H-NMR. data for this compound show that the π-phenyl interactions observed in the solid state occur also in solution. The preparation and NMR.-spectroscopic properties of trans- and cis-[PtH(PPh3) (1)] [BF4] are reported.
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  • 64
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    Helvetica Chimica Acta 64 (1981) 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 65
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Convenient Synthesis of LeucovorinThe synthesis of leucovorin, a 5-formyl-(6R or S)-5,6,7,8-tetrahydropteroyl-L-glutamic acid (II) is described. The L-folic acid was first reduced to (6R, S)-tetrahy-dro-L-folic acid (I); formylation with methyl-formate in DMSO gave directly leucovorin (as a diastereomeric mixture) in good yields. To demonstrate, that the formylation occurred regiospecifically at N (5) and not at N (10), N (10)-nitroso-(6 R, S)-tetrahydro-L-folic acid was formylated under the same conditions. Reductive elimination of the N (10)-nitrosogroup gave the identical leucovorin as in the previous case. The synthetic leucovorin was biologically as active as the natural product with Streptococcus faecalis ATCC 8043 and Pediococcus cerevisiae ATCC 8081.
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  • 66
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    Helvetica Chimica Acta 63 (1980), S. 1335-1346 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Partial Synthesis and Oncostatic Properties of Pseudotubulosines, Analogues of Emetine and TubulosinePseudotubulosines, structural analogues of emetine and tubulosine, have been synthesized by either Pictet-Spengler or Bischler-Napieralski condensation from dihydrocorynantheal or corynantheidal. Spectral data, cytotoxic and oncostatic properties of these new alkaloids are described.
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  • 67
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    Topics: Chemistry and Pharmacology
    Notes: The isotope partition coefficient α between cyclohexane, cycloheptane and hydrogen has been determined between 80 and 180° and pressures around 1 atm. The values decrease with increasing deuterium content y of the hydrogen and can be expressed by the simple equation Ina = Δ S/R + (ΔH + δ · y)/RT with an error of ±1%. However it was not possible to achieve good agreement with theoretical calculations using a unique average value for the partition function of the hydrocarbon.
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  • 68
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    Helvetica Chimica Acta 63 (1980), S. 1400-1406 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metabolites of Microorganisms. FerrithiocinThe strain Tü 1998 from Streptomyces antibioticus produces besides the indicator antibiotics β- and γ-rubromycins a new sulfur containing metabolite. This metabolite, called ferrithiocin, has been isolated in the form of a iron complex. The structure 1 of the iron-free compound was elucidated by spectroscopic studies and chemical degradation.
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  • 69
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of reactions of p-chlorobenzenediazonium ions in aqueous buffer solutions (pH 9.0-10.6) under N2 (〈 5 ppb of O2) have been measured between 20 and 50°C. The formation of trans-diazotate is first-order with respect to the concentration of hydroxyl ions and to the equilibrium concentration of diazonium ions, if the diazonium ion⇄cis-diazotate equilibrium is considered as a fast prior equilibrium. This indicates that the p-chlorobenzenediazonium ion, in contrast to all previous investigations with the p-nitrobenzenediazonium ion and benzenediazonium ions carrying similar substituents with a -M effect, rearranges from the cis- to the trans-configuration as diazohydroxide and not as diazotate. The formation of trans-diazotate is catalyzed by carbonate and inhibited by hydrogen carbonate ions; mechanisms of these catalyses are discussed, and the solvent isotope effect KH2O/KD2O measured by an 1H-NMR. technique reported. The kinetics of the dediazoniations can be analyzed as a mixture of two reactions, a relatively fast first reaction, reaction A, which is responsible for about 5% of the total reaction, and a second reaction F. Both are first-order with respect to diazonium ion; reaction A is also first-order in hydroxyl ions. There are some indications that reaction A corresponds to the hydrolysis of the diazonium ion to give eventually amine and nitrite ions. Reaction F shows a complex dependence on hydroxyl ions; it is related to the homolytic dediazoniation.
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  • 70
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 23Na-chemical shifts for the NaClO4 solute depend markedly upon the composition of binary solvent mixtures of THF with amines (pyridine, piperidine, pyrrolidine, aniline, propylamine, and isopropylamine). These changes, analyzed in a novel application of the Hill formalism, show equality of the intrinsic equilibrium constant K for the successive steps, upon displacement of THF from sodium coordination by one of these amines. The results, which are entirely consistent with tetracoordination of the sodium cation by these solvents, also indicate proportionality of the K values to the amine chemical shifts.
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  • 71
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    Helvetica Chimica Acta 64 (1981), S. 568-571 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylglycine esters react with pyruvic acid to give α-methylsuccinic amides 9 instead of the expected Schiff bases 8, analogously to p-anisidine but unlike aniline.
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  • 72
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: The title compounds have been isolated and their structures determined by X-ray crystallography. Their relative stability is discussed in terms of theory and experiment. The endo-adduct is the thermodynamically more stable one.
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  • 73
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    Helvetica Chimica Acta 64 (1981), S. 572-578 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Notes on the Synthesis of Sulfonated Derivatives of 5,6,7,8-Tetrahydro-1-naphthylamine and 5,6,7,8-Tetrahydro-2-naphthylamineSulfonation of 5,6,7,8-tetrahydro-1-naphthylamine (1) with sulfuric acid gave a mixture of 1-amino-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (2), 4-amino-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (13) and 4-amino-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (3). The same reaction with 5,6,7,8-tetrahydro-2-naphthylamine (20) yielded 3-amino-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (21); formation of 2-amino-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (16) or of 3-amino-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (24) was not observed. Treatment of 4-bromo-5,6,7,8-tetrahydro-1-naphthylamine (4) or of its 4-chloro analogue 5 with amidosulfuric acid gave 1-amino-4-bromo-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (9) and its 4-chloro analogue 10, respectively, which were dehalogenated to 2. Preparations of 13 and 24 were achieved by sulfonation of 5-nitro-1,2,3,4-tetrahydronaphthalene (14) and 6-nitro-1,2,3,4-tetrahydronaphthalene (22) to 4-nitro-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (15) and 3-nitro-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (23), respectively, followed by Béchamp reductions. The sulfonic acid 13 was also obtained by hydrogenolysis of 4-amino-1-bromo-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (11) or of its 1-chloro analogue 12; compounds 11 and 12 were synthesized from N-(4-bromo-5,6,7,8-tetrahydro-1-naphthyl)acetamide (7) and from its 4-chloro analogue 8, respectively, by sulfonation with oleum and subsequent hydrolysis. By ‘baking’ the hydrogensulfate salt of 1 or 20 compounds 3 and 21 were obtained, respectively. Synthesis of 16 was achieved by sulfur dioxide treatment of the diazonium chloride derived from 2-nitro-5,6,7,8-tetrahydro-1-naphthylamine (17) giving 2-nitro-5,6,7,8-tetrahydronaphthalene-1-sulfonyl chloride (18), followed by hydrolysis of 18 to the corresponding sulfonic acid 19 and final reduction.
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  • 74
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Hydrolysis of 6exo-Substituted 2exo- and 2endo-Norbornyl p-Toluenesulfonates. Norbornane Series. Part 3Hydrolysis of the 6exo-substituted 2exo- and 2endo-norbornyl p-toluenesulfonates 1b-1 and 2b-1, respectively, in 70% dioxane led to different amounts of the following products: Unrearranged 2exo-norbornanols 3 and norbornenes 5, accompanied in somes cases by small amounts of the rearranged Rendo-epimers 4 and 6 and by norticyclenes 7. When the 6exo-substituent was a nucleophilic group as in 1e-1 and 2e-1, various amounts of tricyclic products were also formed by endo-cyclization. These results show that the 2exo- and 2endo-esters 1 and 2, respectively, react by way of different intermediates. In cases where the 6exo-substituent was an n-electron donor, as in 1m-r and 2m-r, quantitative fragmentation to (3-cyclopentenyl)acetaldehyde (13) occurred.
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  • 75
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    Helvetica Chimica Acta 63 (1980), S. 2144-2151 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical cations and anions of naphtho [1,8-cd]-[1,2,6]thiadiazine (1) and 6,7-dihydroacenaphtho [5, 6-cd]-[1,2,6]thiadiazine (2), as well as the radical anion of acenaphtho [5, 6-cd]-[1,2,6]thiadiazine (3) have been characterized by ESR. spectroscopy. The π-spin distributions in the radical cations \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\oplus \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\oplus \atop \dot{}}$\end{document} strongly resemble those in the iso-π-electronic phenalenyl radical. A prominent feature of the radical anions \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\ominus \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{\ominus \atop \dot{}}$\end{document} is the substantial localization of the π-spin population on the thiadiazine fragment. These findings are satisfactorily accounted for by HMO models using conventional heteroatom parameters.
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  • 76
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new sesquiterpenoids, nakafuran-8 (1) and -9 (8), have been isolated from the marine sponge Dysidea fragilis and from its prey, the nudibranchs Hypselodoris godeffroyana and Chromodoris maridadilus. The structures were established by spectral analysis and chemical transformations. Both compounds possess antifeedant properties when assayed in the laboratory against common reef fishes, Chaetodon spp.
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    Helvetica Chimica Acta 63 (1980), S. 2179-2186 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereospecific cis-hydroxylation of 1-(2,3-dideoxy-β-D-glyceropent-2-enofuranosyl)thymine (1) into 1-β-D-ribofuranosylthymine (2) by osmium tetroxide is described. Treatment of 2′,3′-O, O-isopropylidene-5-methyl-2,5′-anhydrouridine (8) with hydrogen sulfide or methanolic ammonia afforded 5′-deoxy-2′,3′-O, O-isopropylidene-5′-mercapto-5-methyluridine (9) and 2′,3′-O, O-isopropylidene-5-methyl-isocytidine (10), respectively. The action of ethanolic potassium hydroxide on 5′-deoxy-5′-iodo-2′,3′-O, O-isopropylidene-5-methyluridine (7) gave rise to the corresponding 1-(5-deoxy-β-D-erythropent-4-enofuranosyl)5-methyluracil (13) and 2-O-ethyl-5-methyluridine (14).The hydrogenation of 2 and its 2′,3′-O, O-isopropylidene derivative 4 over 5% Rh/Al2O3 as catalyst generated diastereoisomers of the corresponding 5-methyl-5,6-dihydrouridine (17 and 18).
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  • 78
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    Helvetica Chimica Acta 63 (1980), S. 2221-2229 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemistry of Cyclic Acetals of the 1,3-Dioxa-4,6-cycloheptadiene TypeUV.-irradiation (λ=254 nm) of 3 gives the isomers (E)-5 (4%), (Z)-5 (60%) and 6 (3%). On triplet sensitization (acetone; λ ≥ 280 nm) 3 is converted to (E)-5 (3%), (Z)-5 (7%) and 7 (9%). - The 1π,π*-excitation (λ=254 nm) of 4 yields the isomers 2 (9%), 8 (10%), 9 (34%), 10 (20%) and 11 (3%). On thermolysis (200°) 4 gives 10 (87%) by a Claisen-rearrangement.
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  • 79
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemistry of Conjugated γ,δ-Epoxyenones: The Influence of a Hydroxy Substituent in ∊-PositionOn 1n, π*- or 1π,π*-excitation (λ ≥ 347 or λ=254 nm), the ε-hydroxy-γ;,δ-epoxyenone 8 undergoes fission of the C(γ)—O bond followed by the cleavage of the C(δ)-C(ε) bond. This hitherto unknown sequence of reactions is evidenced by the structure determination of the new type products 10-17 and 25, including a synthetic proof for 12 and the X-ray analysis of 11 (X-ray data: triclinic P1; a=7,386(2), b=8,904(4), c=9,684(5)Å; α=82,29(4)°, β=74,46(3)°, γ=82,29(3)°; Z=2).The selective 1π,π*-excitation also induces competitive C(γ)-C(δ) bond cleavage to yield the bicyclic acetal 18 and a ketonium-ylide intermediate a, which photochemically forms a carbene b giving the allene 19 and the cyclopropene 20.On 1n,π*-excitation of the acetate 9 the initial C(γ)-O bond fission is, in contrast to the behaviour of the corresponding alcohol 8, followed by a 1,2-methyl shift affording (E/Z)-28 or by a cyclization-autoxidation process yielding the lactone 29.
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  • 80
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    Helvetica Chimica Acta 63 (1980), S. 2280-2286 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Synthesis of Sulfonated Derivatives of 4- and 5-AminoindanBaking the hydrogensulfate salt of 4-aminoindan (1) and 5-aminoindan (2) led, respectively, to 4-aminoindan-7-sulfonic acid (3) and 5-aminoindan-6-sulfonic acid (4). Acid 4 was also obtained by direct sulfonation of 2. 4-Aminoindan-6-sulfonic acid (5) and 6-aminoindan-4-sulfonic acid (6) were prepared by sulfonation of 4-nitroindan (7) and 5-nitroindan (9), respectively, to 4-nitroindan-6-sulfonic acid (8) and 6-nitroindan-4-sulfonic acid (10), followed by a Béchamp-reduction. Treatment of 1 with amidosulfuric acid gave 3, whereas the same reaction with 2 led to a mixture of 4 and 5-aminoindan-4-sulfonic acid (11). Independent synthesis of 11 was achieved by the following sequence of reactions: sulfur dioxide treatment of the diazonium chloride derived from 4-amino-5-nitrodan (13) gave 5-nitroindan-4-sulfonyl chloride (14); hydrolysis to 5-nitroindan-4-sulfonic acid (15), and final reduction. The 4-aminoindan-5-sulfonic acid (16) was synthesized by treatment of 4-amino-7-bromoindan (18) with amidosulfuric acid to give 4-amino-7-bromoindan-5-sulfonic acid (19) followed by hydrogenolysis. Sulfonation of 4-acetyl-amino-7-bromoindan (17) with oleum followed by hydrolysis led to 7-amino-4-bromoindan-5-sulfonic acid (20), the structure of which was confirmed by reductive dehalogenation to 5.
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  • 81
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    Helvetica Chimica Acta 63 (1980), S. 2302-2311 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper deals with the problem of defining, and measuring, the pH inside the water pool (which we define as pHwp) of reverse micelles, i.e. micelles formed by surfactants dissolved in apolar solvents in the presence of minimal amounts of water. The conceptual and experimental difficulties are discussed, and it is argued that no absolute determination of pHwp is possible, mostly because water in the water pools of reverse micelles is a new solvent, for which no standardization of acidity is available. The problem can be approached only on the basis of an empirical acidity scale.An empirical acidity scale for water pools in reverse micelles of bis (2-ethyl-hexyl) sodium sulfosuccinate (AOT) in isooctane has been defined by measuring the 31P-chemical shifts of phosphate buffers. The chemical shifts in bulk water were compared to those found in reverse micelles under the assumption that the pK of phosphate ion is the same in the two systems. It was found that in most cases there was little difference (less than 0.4 pH units) between pHwp and the pH of the starting buffer in bulk water (which we define as pHst). However, this difference between pHwp and pHst may become much larger in certain cases.The difference (pHwp-pHst) is measured under a variety of conditions, and this permits the determination of an operational acidity in the micelle water pools as a function of the pHst with which the aqueous micelles are prepared. The significance of such data for interpreting the behaviour of enzymes confined in the micelles water pool is discussed. Based on the pHwp scale, the apparent pKa of phenol-red and 4-nitrophenol were determined in reverse micelles containing different buffers and different water content. The pKa values obtained were rather sensitive to changes of both these factors, which was taken to signify that organic dies have only a very limited applicability to measure the acidity of the water pools of reverse micelles.
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  • 82
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    Helvetica Chimica Acta 64 (1981), S. 1023-1025 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deprotonation of ethyl (E)-2-alkenoates 1, 3 and 4 yields after protonation the double bond migrated (3 Z)-isomers 5, 7 and 9 as major products. In contrast, deprotonation and reprotonation of ethyl (Z)-2-pentenoate (2) gives the (3 E)-isomer 6 exclusively. These findings are explained by reaction paths starting from different ester conformations.
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  • 83
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    Helvetica Chimica Acta 64 (1981), S. 1026-1031 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New Route to 1, 3-Dicarbonyl Derivatives, Model Investigations on the A/B-Part of-3-Oxo-5α-steroidsStarting from 1 the 1, 3-dicarbonyl compounds 4a-d were synthetized via the enynes 2a-e and the relatively unstable epoxides 3a-d. The latter were reacted with 95% formic acid to gave 4a-d; small amounts of the furane derivatives 5a-c were identified as by-products in this last step. In the presence of catalytic amounts of HgSO4 the epoxides 3a-c yielded with 95% formic acid the furanes 5a-c, but no detectable amounts of 4a-c.
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  • 84
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    Helvetica Chimica Acta 64 (1981), S. 1032-1039 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It was found that analysis of the 1H-NMR. signals (at 360 (preferably) and/or 100 MHz) of the protons at C (4) and of the equatorial α-proton at C (6), particularly when these are located in the 2-3 ppm region and therefore convenient for detection and identification, may be of valuable aid in the structural and configurational characterization of 5-hydroxy- and 5-acetoxy-steroids (unsubstituted or containing a hydroxy or acyloxy substituent at C (3)).
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  • 85
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterodiamantanes and Structurally Related Compounds. Part III. The Pentacyclic C11-Diethers 5, 13-Dioxapentacyclo [6.5.0.02,6.03,12.04,9]tridecane, 4, 13-Dioxapentacyclo [6.4.1.02,7.03,10.05,9]tridecane, and 3, 10-Dioxapentacyclo [7.3.1.02,7.04,12.06,11]tridecaneIn connection with the studies on heterodiamantanes and structurally related compounds the three novel pentacyclic diethers 3-5 were prepared starting from the cyclopentadienone dimer 6. All four compounds have as common features a central carbocyclic 6-membered ring with four axial alkyl substituents and two oxygen functions in 1, 4 position. The required eleventh C-atom was introduced by dichlorocarbene addition either to 6 ( → 7) (Scheme 2) or to 29 ( → 28) (Scheme 4).Diether 3 was obtained by reduction of 26 (Scheme 2), a suitable precursor prepared either by intramolecular addition (24 → 26; Scheme 2) or substitution (30 → 26, 31 → 26; Scheme 4), as well as by direct substitution (44 → 3, 42 → 3; Scheme 5). Diether 4 was the product of a direct substitution (39 → 4, 36 → 4; Scheme 5). The synthesis of diether 5 was achieved from the addition product 51 (resulting from the alcohols 47 and 48; Scheme 6).Diether 4 is the thermodynamically least stable of the three diethers 3-5. It was easily isomerized to 5 on treatment with concentrated sulfuric acid in benzene whereas 3 and 5 remained unchanged under these conditions.
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  • 86
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    Helvetica Chimica Acta 64 (1981), S. 1040-1057 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spherical Cryptates. Synthesis and Inclusion-Complexes of Spherical Macrotricyclic LigandsA general strategy for the synthesis of spherical macrotricyclic ligands has been developed. Four spherical cryptands, SC-24, SC-25, SC-26 and SC-27 have been obtained by this route. The synthesis and cation-complexing properties of these compounds are described in detail. Stability constants and cation exchange rates of the spherical cryptates obtained with alkali and alkaline-earth cations have been determined. Highly stable complexes are formed by SC-24; the Rb+ and Cs+ cryptates of SC-24 are the most stable complexes of these cations known to date. The size of the intramolecular cavity affects the complexation selectivity. The cation exchange rates are very slow, and the corresponding free energies of activation are even larger than, for macrobicyclic cryptates of similar stability. Both the high complex stabilities and the high activation energies required for cation exchange indicate a marked ‘spherical cryptate effect’ resulting from the highly connected nature of the molecular architecture of spherical macrotricyclic ligands.
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  • 87
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    Helvetica Chimica Acta 64 (1981), S. 1058-1062 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of proton transfer from 2, 4-hexadiene, 1, 3-cycloheptadiene, cyclopentadiene and acetone to t-butoxide have been measured in the gas phase using pulsed-ion-cyclotron-resonance spectroscopy. The rate constants are (units of 10-10 cm3 molecule-1 s-1): 2.7 ± 0.4, 3.8 ± 0.4, 6.1 ± 0.7 and 10.8 ± 1.5, respectively. These results are analyzed in terms of the properties of the encounter complex and reaction transition states. The reaction profile for t-butoxide + cyclopentadiene is modeled using RRKM theory and an estimate for the central barrier height is obtained.
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  • 88
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 2- and 3-Phenyl Substituted Alkylalkylidene Iminium Ions in the Gas PhaseThe collision-induced fragmentations of 2- and 3-phenyl substituted alkylalkylidene iminium ions are reported. Besides the homolytic cleavage of the azaallyl bond a nucleophilic attack of the unsubstituted phenyl group at the iminium function is observed in the gas phase, yielding carbonium ions such as cyclopropanspirobenzenium (3), indanylium (10) and indenylium ions (11).
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  • 89
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modification of a previously reported synthesis of zeaxanthin (1), and routes to both zeaxanthin and rhodoxanthin (2) from α-ionone, are described.
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  • 90
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition metal complexes often have low-lying excited electronic states and, as a consequence, tend to be electronically labile, i.e., their electronic properties exhibit pronounced sensitivity to external perturbations. Often drastic changes in various spectroscopic properties indicating substantial electronic rearrangements can be induced be relatively weak intermolecular forces as provided by nonpolar solvents or solid molecular host lattices. This behaviour can be explained by crossing of potential surfaces in the vicinity of the absolute minimum. Many physical properties of a given orbitally (near-) degenerate system depend strongly on the relative magnitude of some characteristic parameters determining the shape of the ground Born-Oppenheimer potential surface(s), e.g. barrier height versus zero-point energy, distance between minima versus zero-point amplitude, energy difference between minima, etc. Typical examples are systems exhibiting Jahn-Teller activity, spin-crossover, mixed valence, exchange coupling and other types of electronic near-degeneracies. In paramagnetic systems changes in the electronic wavefunction can be most conveniently detected and analyzed by using EPR. spectroscopy.In paramagnetic sandwich complexes we studied two types of orbital degeneracies: Jahn-Teller degeneracies (d7-systems such as Co (cp)2, Ni(cp)2+ and Fe (cp) (bz), low-spin d5-systems such as Mn (cp)2) and low-spin/high-spin equilibria (d5-systems such as Mn (cp)2). By diluting these complexes and ring-substituted derivatives in a large variety of diamagnetic host systems we have been able to control the 6A/2E equilibrium of Mn (cp)2 by influencing the metal-to-ring distance and by changing the degree of ring alkylation; similarly we have been able to vary the relative weights of the two electronic states contributing to the two-fold degenerate electronic ground state of d5- and d7-systems to a large degree by variation of the local asymmetric fields offered by the lattice sites of the host systems.For comparison the electronic ground state properties of octahedral Cu(II) complexes with CuN6 CuO6 chromophores, of V (CO)6 and tetrahedral VCl4 were also studied by EPR. between 4K and room temperature in several host systems. Characteristic differences in the details of the temperature and host dependence of the EPR. spectra in all these electronically labile systems can be explained in terms of differences in the vibronic coupling type (E ⊗ e vs. T ⊗ e, t), the strength of linear and/or quadratic JT-coupling and the effects produced by spin-orbit coupling.
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  • 91
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Structure of Porphine-type Nickel Complexes Containing Axially Oriented SidechainsThe structure of (±)-[1, 11-dimethoxy-10 H-HDP (2-)]nickel (3), the product of the thermodynamically controlled addition of methanol to [6 H-HDP]nickel-bis-(tetrafluoroborate) (1), was determined by X-ray analysis. The two methoxy groups in 3 are cis-oriented. The syntheses and spectroscopic properties of [1, 11-diethoxy-10 H-HDP (2-)]nickel (5), [1, 11-dineopentyloxy-10 H-HDP (2-)]nickel (6) as well as the bridged complexes [1, 11-pentamethylenedioxy-10 H-HDP (2-)]nickel (4) and [1, 11-(E)-2,3-(dimethyl-2-butenylenedioxy)-10 H-HDP (2-)]nickel (7) are described. Reaction of 1 with bromide ions or 4-methylpyridine leads to the formation of the corresponding hexacoordinated, paramagnetic complexes dibromo [6 H-HDP]-nickel (II) (8) and bis (4-methylpyridine)[6 H-HDP]nickel-bis (tetrafluoroborate) (9).
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  • 92
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe a flexible, stereocontrolled synthesis of enantiomerically pure substituted cyclopentenes and cyclopentanes - including 11α-hydroxy-13-oxaprostanoic acid 20 - (-)-quinic acid via an acyclic precursor 6 by an intramolecular aldolisation-dehydration reaction.
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  • 93
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute conformation of 7-chloro-5-phenyl-1-[(S)-α-phenylethyl]-1, 3-dihydro-2H-1, 4-benzodiazepin-2-one (1c) in crystal, and its inversion rate in solution were determined, enabling prognosis of direction of asymmetric induction during C(3)-alkylation.
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  • 94
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Application of the α-Alkynone Cyclization: Synthesis of rac-Modhephenerac-Modhephene 1, the first sesquiterpene with a propellane C-skeleton and its epimer rac-epi-modhephene 27, were synthesized starting from bicyclo[3.3.0]oct-1(5)-en-2-one (2). The key step in the construction of the [3.3.3]-propellane system is an application of the α-alkynone cyclization, namely 3 → 4 and 11 → 14. The preferred formation of the propellanes 4 and 14 in this step shows that the insertion of the postulated alkylidene carbene intermediate into tertiary C,H-bonds outweighs the one into the secondary ring-C,H-bonds leading to 12/13 and 15/16, respectively. The two starting materials for the α-alkynone cyclization, 3 and 11, were prepared from 2 by the reactions shown in Scheme 3. The further elaboration and separation of the cyclization products 4 and 14 to rac-modhephene 1 and its epimer 27 are outlined in Scheme 5.
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  • 95
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    Helvetica Chimica Acta 64 (1981), S. 389-398 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transformations of 13 alcohols and 13 diols in the presence of a small amount dimethylsulfoxide (1/16 mol) were studied. Relationships were found between the type of the hydroxy compound and the selectivity of the transformation, and conclusions were drawn regarding the transformation mechanism. The ether formation observed with certain alcohols proceeds via a carbenium cation. The reaction conditions applied were found suitable for inducing water elimination from the ditertiary 1,2- and 1,3-diols (pinacol rearrangement, 1,2-elimination). From the 1,4- and 1,5-diols the corresponding oxacycloalkanes can be obtained in good yield. Cyclodehydration occurs by intramolecular nucleophilic substitution, via a concerted mechanism. The effect of DMSO is exerted directly, and protoncatalysis occurs simultaneously.
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  • 96
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    Helvetica Chimica Acta 64 (1981), S. 425-429 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Novel Example of Unsaturated Branched-chain Sugar Nucleoside: 3′-Deoxy-3′-methylidene-adenosineStarting from 5-O-benzoyl-3-C-methylidene-3-deoxy-1,2-O-isopropylidene-α-D-erythro-pentofuranose (11) the title compound 8 has been prepared. Its α-anomer (9) and the acyclic sugar nucleoside 10 have been obtained as by-products. Adenosine deaminase slowly deaminated 8, 9 being not affected. Compound 8 exhibited no antiviral activity, whereas one of its saturated analogues (13) inhibited the multiplication of the herpes-1 (HF) virus.
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  • 97
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    Helvetica Chimica Acta 64 (1981), S. 449-457 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configurational isomers of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) from the flesh of salmon (Salmo salar and Oncorhynchus) caught at different places in Europe and Canada were isolated and analyzed as (-)-camphanic acid diesters by means of HPLC. The biological variation in the composition of the configurational isomers in seven fish was surprisingly similar: 78 to 85% of (3S, 3′S)-astaxanthin, 12 to 17% (3R, 3′R)-astaxanthin and 2 to 6% meso-astaxanthin.
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  • 98
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An interactive system of programs has been developed to assist in structure elucidation based on mass spectral data. The program relies on algorithms for generating all the structural isomers that constitute alternative explanations of the observed data and it associates relative plausibility values with the different isomers. The structure assembly part of the program allows for the use of overlapping substructural components, such as substructures inferred from the appearance of particular ion patterns in the spectrum of an unknown compound. Mass spectrum interpretation procedures used with this structure assembly process could exploit any form of spectrum-substructure correlation scheme. In this work, the emphasis has been on the use of detailed and class specific spectrum-substructure correlations. Applications of the program are illustrated by means of an example analysis of the mass spectra of a variety of marine sterols.
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  • 99
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selective Modification of the Terminal Amide Group of Linear Polyamides via 2-Oxazolin-5-ones as IntermediatesTreatment of aqueous or alcoholic solutions of diamides of type 2 with HCl leads to the formation of amide-acids and amide-esters of type 3 (Scheme 1 and Table). It has been shown, that 2-oxazolin-5-ones of type 4 are intermediates of this selective transformation of the disubstituted terminal amide group. The selectivity of the transformation is demonstrated by the reaction sequence shown in Scheme 3. No selectivity has been observed in the acid-catalyzed hydrolysis of triamide 9 with a monosubstituted terminal amide group (Scheme 4). Hydrolysis of the optically active dipeptide derivatives (+)-(L)-13 and (+)-(L)-15 with HBr in nitromethane at 60-80° yields the pure enantiomer (+)-(L)-14 and (+)-(L)-16, respectively (Scheme 5), i.e., no racemization takes place under the reaction conditions.These results show the usefulness of the dimethylamide group as a protecting group for carboxylic acids for example in the peptide synthesis.
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  • 100
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N-CIDNP. spectra recorded during the reaction of diazonium cations with OH- in weakly alkaline aqueous solutions show that the dediazoniation is at least partially homolytic. The polarizations observed for the diazonium and trans-diazotate ions can be explained by reaction proceeding via a cage involving diazenyl and diazotate radicals using Kaptein's rules and simple intensity considerations.
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