Substituent Effect on Acidity of Substituted 2-(4-Nitrobenzoylamino)alkanamides in Methanol-Dimethyl Sulfoxide Mixtures

1998 ◽  
Vol 63 (1) ◽  
pp. 85-93 ◽  
Author(s):  
Petr Mitaš ◽  
Miloš Sedlák ◽  
Jaromír Kaválek
Keyword(s):  
Carbon Atom ◽  
Dimethyl Sulfoxide ◽  
Substituent Effect ◽  
Dissociation Constants ◽  
Point Of View

The dissociation constants of substituted 2-(4-nitrobenzoylamino)alkanamides, N-[2-(4-nitrobenzoylamino)alkanoyl]pyrrolidines, and N-alkyl-4-nitrobenzamides have been measured spectrophotometrically in 60 and 80% v/v DMSO. The pKA values of these N-acids are discussed from the point of view of substituents at the acetamide α-carbon atom.

scholarly journals PROTOLYTIC EQUILIBRIUM OF TETRA- AND PENTANITROFLUORESCEINS IN A BINARY SOLVENT ACETONITRILE – DIMETHYL SULFOXIDE (MASS RATIO 96 : 4)

2021 ◽  
Vol 87 (5) ◽  
pp. 25-37
Author(s):  
Elena Moskaeva ◽  
Ahina Mosharenkova ◽  
Sergey Shekhovtsov ◽  
Nikolay Mchedlov-Petrossyan
Keyword(s):  
Dimethyl Sulfoxide ◽  
Dissociation Constants ◽  
Equilibrium Constants ◽  
Equilibrium Mixture ◽  
Point Of View ◽  
Anionic Form ◽  
Binary Solvent ◽  
Carboxylic Group ◽  
Tautomeric Equilibria ◽  
The Difference

In this paper, the acid-base and tautomeric equilibria of four nitrofluorescein dyes, 2,4,5,7-tetranitrofluorescein, 2,4,5,7,4’-pentanitrofluorescein, 2,4,5,7,5’-pentanitrofluorescein, and 2,4,5,7-tetranitrofluorescein methyl ester, were studied. As reaction media, a binary solvent acetonitrile – dimethyl sulfoxide (96 : 4 by mass) was used. The acidity scale in this solvent was established previously. The indices of the dissociation constants of the dyes were determined using the spectrophotometric method. Interpreting the  values ​​requires an understanding of the state of tautomeric equilibria. The behavior of these compounds differs significantly from that of other fluorescein dyes, e.g., halogen derivatives. In the case of the first three compounds, i.e., for dyes with a free carboxylic group, the lactonic structure is predominant not only for the neutral form, but even for the double-charged anion. The single-charged anionic form exists as an equilibrium mixture of a colored (and fluorescent) tautomer and an almost colorless lactone. The fourth compound with esterified carboxylic group exhibits extreme stability in its anionic form.  Evaluation of the tautomerization constants made it possible to calculate the microscopic equilibrium constants of the stepwise dissociation of dye lactones, k1L and k2L. The consideration of the difference (pk2L – pk1L) allowed estimating the effective relative permittivity of the space between the ionizing groups basing on the Bjerrum – Kirkwood – Westheimer equation. Tautomerism of anions was discussed from the point of view of stabilization of symmetric structures.

Separation of the Enthalpic and Entropic Contributions to Substituent Effects for the Equilibrium Constants of Aromatic Acids

1975 ◽  
Vol 53 (23) ◽  
pp. 3622-3633 ◽  
Author(s):  
T. M. Krygowski ◽  
W. R. Fawcett
Keyword(s):  
Substituent Effect ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Point Of View ◽  
Aromatic Acids ◽  
Resonance Effects ◽  
Equation Analysis ◽  
Reaction Constant ◽  
Enthalpy And Entropy Changes ◽  
Substituent Constants

Separation of the substituent effect ρσ into entropie ρSσS and enthalpic ρHσH contributions is presented within the framework of the general Hammett equation. Analysis of the experimental data for aromatic acids shows that, in general, entropie effects are the major contribution to the total substituent effect, the entropic reaction constant being approximately equal to the normal Hammett ρ A comparison of the present results with those based on a separation of inductive and resonance effects shows that the entropie and inductive effects are directly related. On the other hand, strongly resonance interacting substituents were found to be enthalpy controlled. The substituent effect on enthalpy and entropy changes is discussed from a molecular point of view and related to inductive and resonance effects. A list of 16 enthalpic (σH) and entropie (σS) substituent constants are presented.

scholarly journals The reaction of ornithine aminotransferase with ornithine

1982 ◽  
Vol 201 (1) ◽  
pp. 221-225 ◽  
Author(s):  
J A Williams ◽  
G Bridge ◽  
L J Fowler ◽  
R A John
Keyword(s):  
Amino Acids ◽  
Carbon Atom ◽  
Rat Liver ◽  
Dissociation Constants ◽  
Amino Group ◽  
Ornithine Aminotransferase ◽  
Mammalian Enzyme ◽  
Kinetics Of ◽  
Plant Enzyme

Rat liver ornithine aminotransferase is found to exchange the pro-S hydrogen on the delta-carbon atom of ornithine exclusively, thus showing that the mammalian enzyme transfers the delta-amino group and not the alpha-amino group as has been demonstrated with the plant enzyme [Mestichelli, Gupta & Spenser (1979) J. Biol. Chem. 254, 640-647]. The enzyme also transfers the alpha-amino group of glutamate and the kinetics of the half reactions between the enzyme and both amino acids are compared. Rate and dissociation constants for both reactions are determined.

Re-examination of the Kirkwood–Westheimer theory of electrostatic effects. III. Dissociation constants of cis-3- and trans-4-substituted cyclohexanecarboxylic acids in water–dimethyl sulfoxide mixtures

1978 ◽  
Vol 56 (8) ◽  
pp. 1130-1133 ◽  
Author(s):  
Jitka Kirchnerova ◽  
Patrick G. Farrell ◽  
John T. Edward ◽  
Jean-Claude Halle ◽  
Robert Schaal
Keyword(s):  
Dimethyl Sulfoxide ◽  
Dissociation Constant ◽  
Dissociation Constants ◽  
Solvent Composition ◽  
Potentiometric Method ◽  
Acid Dissociation ◽  
Electrostatic Effects ◽  
Acid Dissociation Constants ◽  
Cyclohexanecarboxylic Acid

Acid dissociation constants of two cis-3- and of four trans-4-substituted cyclohexanecarboxylic acids in water – dimethyl sulfoxide mixtures of varying composition were determined by a potentiometric method. Results have been analyzed according to the model of Kirkwood and Westheimer, and shown to differ from calculated values because of certain oversimplifications built into the model. Dissociation constant differences between cyclohexanecarboxylic acid and the compounds studied vary only slightly with changing solvent composition.

Dissociation constants of uncharged and monovalent cation acids in dimethyl sulfoxide

1968 ◽  
Vol 90 (1) ◽  
pp. 23-28 ◽  
Author(s):  
Izaak M. Kolthoff ◽  
Miran K. Chantooni ◽  
Sadhana. Bhowmik
Keyword(s):  
Dimethyl Sulfoxide ◽  
Dissociation Constants ◽  
Monovalent Cation

Main Allotropes of Carbon

2017 ◽  
pp. 185-213
Author(s):  
Zahra Khalaj ◽  
Majid Monajjemi ◽  
Mircea V. Diudea
Keyword(s):  
Carbon Atom ◽  
Vapor Deposition ◽  
Carbon Nanostructures ◽  
Chemical Vapor ◽  
Point Of View ◽  
Diamond Like Carbon ◽  
Chemical Bonds ◽  
High Quality ◽  
Carbon Allotropes ◽  
Experimental Parameters

Carbon allotropes can be classified according to the carbon atom hybridization. In principle, there are different ways, based on various parameters, such as range dimensionality, type of chemical bonds, etc. which can be used to classify carbon nanostructures. Classifications vary function of the field of nanostructure applications. In a point of view, one can classify the carbon allotropes by the type of carbon atom hybridation. This chapter is a brief review introduction to some major allotropes: graphene/graphite, carbon nanotubes, diamond and amorphous carbon. In addition, Chemical Vapor Deposition (CVD) techniques, frequently used for synthesizing these structures are discussed. The influence of some important experimental parameters on the growth of high quality diamond and diamond-like carbon DLC are also investigated.

Dissociation constants of substituted benzoic acids in water and in organic solvents

1986 ◽  
Vol 51 (10) ◽  
pp. 2135-2142 ◽  
Author(s):  
Miroslav Ludwig ◽  
Václav Baron ◽  
Karel Kalfus ◽  
Oldřich Pytela ◽  
Miroslav Večeřa
Keyword(s):  
Potentiometric Titration ◽  
Organic Solvents ◽  
Solvent Effects ◽  
Dissociation Constants ◽  
Point Of View ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Substituent Constant ◽  
Reaction Constant ◽  
Substituted Benzoic Acids

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.

Solute–solvent effects in the dissociation of thymolsulfonephthalein (an uncharged acid) in aqueous mixtures of acetonitrile (ACN), urea, and dimethyl sulfoxide (DMSO)

1986 ◽  
Vol 64 (8) ◽  
pp. 1521-1526 ◽  
Author(s):  
A. L. De ◽  
A. K. Atta
Keyword(s):  
Solvent Effect ◽  
Dimethyl Sulfoxide ◽  
Solvent Effects ◽  
Mixed Solvent ◽  
Dissociation Constants ◽  
Aqueous Mixtures ◽  
Solvent Interactions ◽  
Gibbs Energies ◽  
Gibbs Energies Of Transfer ◽  
Solvent Systems

The thermodynamic first dissociation constants, [Formula: see text] of thymolsulfonephthalein (H2A), an uncharged acid, have been determined at 25 °C in aqueous mixtures of 10, 30, 50, 70, and 80 wt% acetonitrile (ACN), 11.52, 20.31, 29.64, and 36.83 wt% urea, 20, 40, 60, and 80 wt% dimethyl sulfoxide (DMSO) by spectrophotometric measurements. The solvent effect represented by ∂(ΔG0) = 2.303RT[p(sK)N − p(wK)N] is found to increase in ACN + H2O system as mol% ACN increases in the solvent. In contrast, the corresponding values in urea + H2O as well as DMSO + H2O solvent systems decrease with increase in proportion of organic component in the solvent, the decrease being sharp in urea + H2O. The results have been discussed in terms of the standard Gibbs energies of transfer of H+ from water to the mixed solvent, [Formula: see text] and the relative values of the standard Gibbs energies of transfer of HA−, [Formula: see text] and of [Formula: see text] in all the solvent systems. The overall dissociation behaviour of the acid (H2A) is found to be dictated by the specific solute-solvent interactions of the species participating in the dissociation equilibria.

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