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  • 1
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of bridged calix [4] arenes (5-10 methylene groups in the bridge) were synthesized and transformed into their tetraester derivatives by reaction with ethyl bromoacetate. The stability constants for complexes of the tetraester derivatives with sodium, potassium and silver cations, determined in methanol by spectroscopic or potentiometric techniques, show a drastic decrease (more than 105 for Na +) for the shorter methylene chains. 1H NMR studies demonstrate a conformational rearrangement of the calixarene part to fourfold symmetry to be necessary for the complexation of a cation, which is prevented by the shorter chains. This is further confirmed by the X-ray structure of a tetraester derivative with a CH2CH2COCH2CH2 bridge; crystals were monoclinic, space group P21/c,a = 11.847(2), b = 39.773(5), c = 12 · 127(2) Å, β = 109.24(1), V = 5395.1 Å3, Z = 4, Dx = 1.186 Mg m-3.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 80-89 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Measured pseudo-first-order rate constants for intramolecular formation of tetrahedral intermediates from N-2-hydroxyethylphthalimide, N-2-aminoethylphthalimide and N-2-thioethylphthalimide at pH 〉 6 are reported. The reaction is specific and general base catalysed, with β(Brønsted) values 0·44, 0·52 and 0·52 respectively. From a plot of log kb (general base rate constants) vs γ′ [the affinities of EtXH (X = O, NH, S) toward the carbonylic carbon], β′nuc values of 0·01 (with OH- as specific base), 0·25 (with imdidazole as general base) and 0·27 (with HPO42- as general base were obtained). The observed relationships pxy = ϑβ′/ - ϑpKa = -ϑ(Brønsted)/ϑγ′ = 0·03 is supported by the predictions of an energy contour diagram, which, on extrapolation to a non-stable tetrahedral intermediate, predicts a late and slightly protonated transition state for the cleavage process. At pH 〈 3, these intermediates cleave to yield only the corresponding diacylimides. These reactions are general base and acid catalysed with β 〉 0·3 and α 〈 0·1. A fast equilibrium between the intermediate and its N-protonated (amide) form is reached. The general base rupture of the latter is faster than that of the corresponding non-protonated intermediate by a factor of ca 109 - 1010-fold.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 585-590 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The title sulphenamides were pyrolysed in a stirred-flow reactor at temperatures of 310-410°C, pressures of 8-15 Torr and residence times of 0·4-2 s using toluene as the carrier gas. N-(tert-Butylthio)allylamine formed 73 ± 4% isobutene, 23 ± 3% propene and N-allylthiohydroxylamine. The first-order rate coefficients for the formation of isobutene and propene, respectively, followed the Arrhenius equations kC4(s-1) = 1012·52 ± 0·36 exp(-163 ± 5 kJ mol-1 RT) and kC3(s-1) = 1010·99 ± 0·29 exp(-151 ± 4 kJ mol-1 RT) N-(tert-Butylthio)diethylamine gave 97 ± 1% isobutene, 1·9 ± 0·4% isobutane and N,N-diethylthiohydroxylamine. The first-order rate coefficients for isobutene elimination followed the Arrhenius equation k(s-1) = 1013·45 ± 0·24 exp(-164 ± 3 kJ mol-1 RT). The formation of the products is interpreted in terms of an elimination reaction with a unimolecular, four-centered, cyclic transition state. The reactivity of these sulphenamides was found to be much higher than that of previously studied alkyl or aryl tert-butyl sulphides and disulphides.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 22 (1990), S. 1271-1282 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article reports the kinetics of the decomposition of N-bromoserine formed rapidly by bromation of serine by BrO-. The main decomposition products are glycolaldehyde, ammonia, carbon dioxide, and bromide ions at pH 〈 11.5, and β-hydroxypyruvic acid, ammonia, and bromide ions at pH 〉 11.5. The reaction is of order one with respect to N-bromoserine, and is independent of ionic strength and excess serine. The rate constant increases with increasing pH at pH 〉 11 and with decreasing pH at pH 〈 8, and over the range pH 8-11 has the constant value 1.67 × 10-3 s-1 at 298 K.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 991-997 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the disproportionation of N — Cl-n-propylamine and N - Cl-isopropylamine to the corresponding N, N-dichloramines were found to be a second order with respect to the N-chloramine. The influence of amine concentration, pH, buffers, ionic strength, and temperature were also studied. The observed influence of pH supports a reaction mechanism which allowed estimation of the protonation constants of the chloramines studied. The influence of buffers, which was studied for both the above chloramines and N — Cl-3-aminopropanol, reflects general acid catalysis, for which a mechanism is proposed. Bronsted's equation was fitted to the catalytic constants obtained therefrom so as to estimate the values of the parameter α for these three N-chloramines. © John Wiley & Sons, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 26 (1994), S. 593-594 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 17 (1985), S. 583-590 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effective energy distribution of activated molecules at the time of reaction under soft collision conditions ƒ′(E, ω) is pressure dependent and therefore difficult to recover from unimolecular decomposition data obtained at different pressures. We show in this work that the part of this function restricted to the condition that the collision frequency ω has to be equal to the microscopic rate constant k(E) at the energy given ƒ″[E,ω = k(E)] is a reasonable approximation to the input energy distribution ƒ(E) for quite soft collisions. This function is not pressure dependent and then recoverable at least in principle and as a matter of fact is not conceptually far from the function that the already reported deconvolution methods based in physical approximations attempt to recover. The deconvolution methods have been checked under soft collision conditions. We have found that the input energy distribution is recovered with reasonable accuracy for energies transferred by collision 〈ΔE〉 above 5 kcal mol-1, conditions common in polyatomic systems.
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  • 8
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between Co(en)2(2-pzCO2)2+ (bis-ethylenediamine (2-pyrazinecarboxylato)cobalt(III)) and Fe(CN)5H2O3- (aquopentacyanoferrate(II)) to form the binuclear complex [(en)2Co( μ-pzCO2)Fe(CN)5]- has been studied in several isodielectric binary mixtures at 298.2 K (cosolvents: methanol, ethanol, tertbutyl alcohol, ethyleneglycol, and glycerol). Results were rationalized by using a free energy relationship. The importance of correcting the rate constants obtained in the different mixtures from the ionic strength influence has been shown. © 1995 John Wiley & Sons, Inc.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 28 (1996), S. 353-359 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The amide derivatives of t-butylsulfenic acid mentioned in the title have been thermolyzed in a stirred-flow reactor at temperatures of 273-390°C and pressures of 7-15 torr, using toluene as carrier gas, at residence times of 0.4-2 s. Isobutene formed in 95-99% yields, through order one reactions, following the Arrhenius equations: N, N-dimethyl t-butylsulfenamide: $$k(s^{-1})=10^{14.45\pm 0.46}\exp(-175\pm 5 {\rm kJ/mol}\,{\bf RT})$$ 2,6-dimethylpiperidyl t-butylsulfenamide: $$k(s^{-1})=10^{14.38\pm 0.26}\exp(-161\pm 3 {\rm kJ/mol}\,{\bf RT})$$ N-t-butyl t-butylsulfenamide: $$k(s^{-1})=10^{14.75\pm 0.37}\exp(-184\pm 7 {\rm kJ/mol}\,{\bf RT})$$These thermolyses are considered to take place through unimolecular, four-center cyclic transition-state reaction mechanisms, giving rise to isobutene plus the corresponding S-unsubstituted thiohydroxylamines. The latter decompose outside the reactor at temperatures above -78°C forming free sulfur and dimethylamine, 2,6-dimethylpiperidine, and t-butylamine, respectively. © 1996 John Wiley & Sons, Inc.
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  • 10
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-chloro-3-aminopropanol was obtained in aqueous solution by mixing the amine with the hypochlorite. The first order decomposition kinetics of the N-chloramine in strongly alkaline media are explained by a mechanism in which the rate controlling step is the formation of an imine which is subsequently hydrolyzed. Spectrophotometry of the reaction in acid media showed that under these conditions dichloramines are formed: the second order experimental kinetics of this process are explained by a mechanism in which the rate-controlling step is a reaction between the protonated and free forms of the N-chloramine.
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