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  • 1
    Online Resource
    Online Resource
    Solvent effect in dissociation of substituted benzenesulphonamides in dimethylformamide, dimethyl sulphoxide, and acetonitrile
    Institute of Organic Chemistry & Biochemistry ; 1984
    In:  Collection of Czechoslovak Chemical Communications Vol. 49, No. 11 ( 1984), p. 2593-2601
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 49, No. 11 ( 1984), p. 2593-2601
    Abstract: Dissociation constants of fifteen substituted arenesulphonamides of general formula XC 6 H 4 .SO 2 NH 2 (or X 2 C 6 H 3 SO 2 NH 2 ) have been measured by potentiometric titration in dimethylformamide, dimethyl sulphoxide, and acetonitrile. The Hammett substitution correlations have been calculated and interpreted for these media. The p K HA values measured and the results published earlier for methanol, ethanol, and water have been treated by multiple linear regresion using the published set of the parameters characterizing solvents and by factor analysis using the short cycle and the target testing method.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19842593
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1984
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  • 2
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    Online Resource
    Reactions of substituted 1,3-diphenyltriazenes with phenyl isocyanates. Catalysis and substituent effects
    Institute of Organic Chemistry & Biochemistry ; 1980
    In:  Collection of Czechoslovak Chemical Communications Vol. 45, No. 4 ( 1980), p. 1279-1289
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 45, No. 4 ( 1980), p. 1279-1289
    Abstract: Reactions of phenyl isocyanate with 12 monosubstituted and 15 symmetrical disubstituted 1,3-diphenyltriazanes have been studied in tetrahydrofurane at 25°C. The found rate constants correlate with the Hammett substituent constants, the slopes being - 1.206 and - 1.682 in case of the monosubstituted and the disubstituted compounds, respectively. Under conditions of pseudomonomolecular reaction catalysis by the products and that by the catalysts used in reactions of isocyanates with amines or hydroxy compounds have not been observed. Rates of reactions of 6 substituted phenyl isocyanates with the parent 1,3-diphenyltriazane have also been measured. In this case the found rate constants correlate with the Hammett substituent constants, the slope being +1.038. The results indicate that the reaction involves rate limiting formation of a six-membered cyclic complex which successively undergoes only a rapid reorganization of electrons.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19801279
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1980
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  • 3
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    Online Resource
    Dissociation constants of substituted benzoic acids in water and in organic solvents
    Institute of Organic Chemistry & Biochemistry ; 1986
    In:  Collection of Czechoslovak Chemical Communications Vol. 51, No. 10 ( 1986), p. 2135-2142
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 51, No. 10 ( 1986), p. 2135-2142
    Abstract: Potentiometric titration has been used to measure dissociation constants of 38 monosubstituted benzoic acids in water and in 6 organic solvents (methanol, ethanol, dimethylformamide, acetonitrile, sulfolane, acetone). The results have been analyzed and interpreted from the point of view of substituent and solvent effects on the dissociation of the title substrates. It has been proved that solvents affect not only the reaction constant but also the substituent constant of the Hammett equation.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19862135
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1986
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  • 4
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    Online Resource
    Kinetics and Mechanism of Decomposition of 1,3-Bis(4-methylphenyl)triazene Catalyzed with Substituted Benzoic Acids in 25% Aqueous Methanol-General or Specific Catalysis?
    Institute of Organic Chemistry & Biochemistry ; 1994
    In:  Collection of Czechoslovak Chemical Communications Vol. 59, No. 9 ( 1994), p. 2029-2041
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 59, No. 9 ( 1994), p. 2029-2041
    Abstract: The kinetics of decomposition of 1,3-bis(4-methylphenyl)triazene catalyzed with 13 substituted benzoic acids of various concentrations have been measured in 25 vol.% aqueous methanol at 25.0 °C. The rate constants observed (297 data) have be used as values of independent variable in a series of models of the catalyzed decomposition. For the catalytic particles were considered the undissociated acid, its conjugated base, and the proton in both the specific and general catalyses. Some models presumed formation of reactive or nonreactive complexes of the individual reactants. The substituent effect is described by the Hammett equation. The statistically best model in which the observed rate constant is a superposition of a term describing the dependence on proton concentration and a term describing the dependence on the product of concentrations of proton and conjugated base is valid with the presumption of complete proton transfer from the catalyst acid to substrate, which has been proved. The behaviour of 4-dimethylamino, 4-amino, and 3-amino derivatives is anomalous (lower catalytic activity as compared with benzoic acid). This supports the presumed participation of conjugated base in the title process.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19942029
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1994
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  • 5
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    Online Resource
    Kinetics and Mechanism of Acid Catalysed Hydration of α-Methylstyrenes
    Institute of Organic Chemistry & Biochemistry ; 2007
    In:  Collection of Czechoslovak Chemical Communications Vol. 72, No. 8 ( 2007), p. 1025-1036
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 72, No. 8 ( 2007), p. 1025-1036
    Abstract: Twelve para -substituted α-methylstyrenes with substituents H, CH 3 , CF 3 , CH 3 O, CH 3 S, F, Cl, Br, CH 3 CO, CH 3 SO 2 , CN a NO 2 were synthesised; additionally, the acid catalysed hydration kinetics of these compounds were measured in sulfuric acid in a concentration range c from 0.017 to 9.58 mol l -1 , at 25.0 °C. The observed rate constants obtained were used to construct the kinetic acidity function and calculate the catalytic rate constants. Based on the evaluation of the acidity function kinetic dependence on acid medium concentration, and the substituent effects of acid catalysed hydration of α-methylstyrenes on the catalytic rate constants, the mechanism of acid catalysed hydration was verified. The mechanism involves the addition of a proton to the double bond of α-methylstyrene in the rate-limiting reaction step denoted as A-SE2. No evident difference was found between the effects of the acid medium on the acid catalysed hydration of styrenes and α-methylstyrenes, which indicates very similar activity coefficients of the reactants, and of the transition state of both substrates. The substituent effects evaluation shows that the rate-limiting step of the reaction consists in the addition of a proton to the substrate. The carbocation formation in the transition state of this reaction step proceeds roughly half-way compared with the extent of the carbocation formation by cumyl chloride hydrolysis. The obtained carbocation is in particular stabilised by the substituents with + M effect, while the influence of the substituents with - M and I effects is significantly smaller.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc20071025
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 2007
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  • 6
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    Online Resource
    Kinetics of acid catalyzed decomposition of substituted 1,3-diphenyl-3-methyltriazenes
    Institute of Organic Chemistry & Biochemistry ; 1986
    In:  Collection of Czechoslovak Chemical Communications Vol. 51, No. 3 ( 1986), p. 553-563
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 51, No. 3 ( 1986), p. 553-563
    Abstract: Kinetics of the acid catalyzed decomposition of fifteen 1-substituted-1,3-diphenyl-3-methyltriazenes have been studied in 40% aqueous ethanolic buffers at 25 °C. The slope found for the dependence log k obs vs pH of the buffer is not equal to unity, and a method of treating such experimental data is suggested. The reaction constant found (ρ = -3.70) indicates that substituents have similar effects on both protonation and decomposition of the triazene chain.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19860553
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1986
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  • 7
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    Online Resource
    Chemometric Analysis of Substituent Effects. XII. Application of Relationship Between 2- and 4-Substitution of Benzene Ring to Study ortho Effect in Selected Compounds with Different Reaction Centres
    Institute of Organic Chemistry & Biochemistry ; 1999
    In:  Collection of Czechoslovak Chemical Communications Vol. 64, No. 10 ( 1999), p. 1617-1628
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 64, No. 10 ( 1999), p. 1617-1628
    Abstract: Three model compounds have been selected to study the relationship between ortho and para substitution: benzoic acid, phenol, and aniline. Sixteen substituents have been chosen involving also those capable of potential interaction between ortho substituent and the reaction centre. For the combinations given, literature presents 25 pairs of data obtained by measuring a particular process for both the ortho and para substituted derivatives. The missing dissociation constants of 16 ortho substituted benzoic acids in water and ethanol and 16 para substituted benzoic acids in dimethyl sulfoxide and pyridine have been measured by potentiometric titration. The data matrices were submitted to analysis by the methods of projection of latent structures (PLS) and principal component analysis (PCA). It has been found that the substituent effects from ortho and para positions have the same character unless the ortho substituents interact with the reaction centre. Such interactions can change the experimentally found value by as much as 20% of its magnitude. The most significant interaction is a hydrogen bond formation. Out of the three models studied the most extensive interactions are present in benzoic acid, whereas almost none were observed in aniline. The capability of donation of electron pair to a hydrogen bond decreases in the substituent series COCH 3 〉 SO 2 CH 3 〉 NO 2 . The capability of donation of proton to a hydrogen bond with electron-pair donor decreases in the substituent series OH 〉 NHCOCH 3 ≈ SH 〉 NH 2 〉 SO 2 NH 2 .
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19991617
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1999
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  • 8
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    Online Resource
    Chemometric Analysis of Substituent Effects. IX. Alternative Interpretation of Substituent Effects (AISE) - Orthogonal Model
    Institute of Organic Chemistry & Biochemistry ; 1996
    In:  Collection of Czechoslovak Chemical Communications Vol. 61, No. 5 ( 1996), p. 704-712
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 61, No. 5 ( 1996), p. 704-712
    Abstract: Continuing the previous communications, the present paper suggests an orthogonal model of alternative interpretation of substituent effects (AISE). Following this approach, substituents are classified into three classes. Those of class II are defined as substituents whose atom bound to the basic skeleton bears a character of nucleophile, i.e. it is able of an intramolecular nucleophilic interaction with the reaction centre. The class III includes substituents whose atom bound to the basic skeleton is electrophilic in nature and can correspondingly interact with the reaction centre too. The class I includes the substituents possessing none of the above-mentioned characteristics. Within the model suggested the substituent effects can be described by a family of three lines corresponding to the substituent classes described with a single substituent constant at the coordinate axis. The validity of the model suggested has successfully been tested by comparison with other correlation equations using 318 reaction series taken from literature. It has been found that the value of the point of intersection at the coordinate axis (the isosubstituent constant) is smaller in processes with electron deficit and grater in those with electron excess in the reaction centre. The slopes of the individual lines in the family of lines (the reaction constants) decrease in the order II 〉 I 〉 III in most cases, the only exception being the processes with direct conjugation between a negatively charged reaction centre and the substituent and some gas phase processes.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19960704
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1996
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  • 9
    Online Resource
    Online Resource
    Reactivity of proton and general acid with 1,3-bis-(4-methylphenyl)triazene in aqueous methanol
    Institute of Organic Chemistry & Biochemistry ; 1990
    In:  Collection of Czechoslovak Chemical Communications Vol. 55, No. 11 ( 1990), p. 2701-2706
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 55, No. 11 ( 1990), p. 2701-2706
    Abstract: The effect of concentration of benzoic acid and composition of the binary solvent water-methanol on the rate of decomposition of 1,3-bis(4-methylphenyl)triazene has been studied. It has been found that both general acid catalysis by undissociated benzoic acid and catalysis by the proton are significant. The rate constant k HA of general acid catalysis decreases monotonously with decreasing amount of water in the mixture due to preferred solvation of the activated complex as compared with the educts. The rate constant k H of the catalysis by proton in its dependence on methanol concentration exhibits a minimum for 80% (by wt.) of methanol in the mixture. This phenomenon is caused by formation of the conjugated acid from more basic methanol and proton with simultaneous solvation by water and methanol; the particle thus formed is a weaker acid as compared with the complexes existing in water or in methanol. The k H value is higher in methanol than in water due to preferred solvation of the educts as compared with that of the transition state.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19902701
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1990
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  • 10
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    Online Resource
    Kinetics and Mechanism of Acid Catalyzed Decomposition of 1-Phenyl-3,3-dialkyltriazenes
    Institute of Organic Chemistry & Biochemistry ; 1994
    In:  Collection of Czechoslovak Chemical Communications Vol. 59, No. 2 ( 1994), p. 401-411
    Details
    In: Collection of Czechoslovak Chemical Communications, Institute of Organic Chemistry & Biochemistry, Vol. 59, No. 2 ( 1994), p. 401-411
    Abstract: Five model 1-phenyl-3,3-dialkyltriazenes (methyl, ethyl, 2-propyl, butyl, cyclohexyl) have been synthesized and their acid-catalyzed decomposition kinetics have been investigated spectrophotometrically in aqueous ethanol (40 vol.%) with pivalic acid as the catalyst. The results show that the rate-determining step is catalyzed by the proton. The decrease in the observed rate constant at higher concentrations of pivalic acid is explained by the formation of an unreactive complex of the nondissociated acid and respective triazene. The steric effect of alkyl groups on the catalytic rate constants is discussed.
    Type of Medium: Online Resource
    ISSN: 0010-0765 , 1212-6950
    URL: Article
    DOI: 10.1135/cccc19940401
    Language: English
    Publisher: Institute of Organic Chemistry & Biochemistry
    Publication Date: 1994
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