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Solvent Parameters (solvent + parameter)
Selected AbstractsCorrelations and predictions of solvent effects on reactivity: some limitations of multi-parameter equations and comparisons with similarity models based on one solvent parameterJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2006T. William Bentley Abstract Three recent publications on multi-parameter correlations of solvent effects on solvolytic reactivity are re-examined, by considering ,similarity' and/or ,analogy'. Systematic errors due to compensation effects and to comparisons between dissimilar processes are found. Models for solvent nucleophilicity involving dissimilar spectroscopic processes (e.g. , or B parameters) give insensitive measures of low nucleophilicity. From qualitative considerations based on structural similarities, it is predicted that the sensitivities to changes to solvent polarity for solvolyses of chloroalkanes should be in the order: 1-adamantyl (3),>,2-methyl-2-adamantyl (1),>,t -butyl (2). The predictions are confirmed quantitatively by simple linear free-energy relationships and similarity models, involving correlations with YCl (based on solvolyses of 1-chloroadamantane) or ET(30) (based on solvatochromism). Multi-parameter correlations, indicating that solvolyses of 1 show a low sensitivity to both solvent polarity and electrophilicity, and also a negative sensitivity to solvent nucleophilicity, are shown to be unreliable. Large errors are also evident in recent KOMPH2 calculations. Conclusions are supported by comparing several multi-parameter treatments of solvolyses of 4-methoxyneophyl tosylate, for which there is a reliable set of kinetic data and a generally accepted mechanism. Copyright © 2006 John Wiley & Sons, Ltd. [source] Simulation and Experiment of Temperature and Cosolvent Effects in Reversed Phase Chromatography of PeptidesBIOTECHNOLOGY PROGRESS, Issue 3 2005Kosta Makrodimitris Experiments and simulations have been carried out for several polar protected peptides in reversed phase chromatography in order to demonstrate how simulation can describe the effects of varying temperature and cosolvent fraction. Comparisons of adsorption chemical potentials from mesoscopic simulations and experimental chromatographic retention data show very good agreement with only one temperature-independent solvent parameter from a single peptide. Such simulations should help guide the design of chromatography experiments with biomolecules and predict retention, including conditions for which empirical correlations such as hydrophobicity scales and molecular descriptors have not been developed. [source] Preferential solvational effects on the Cr(VI) oxidation of benzylamines in benzene/2-methylpropan-2-ol mixturesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2010A. Thirumoorthi Imidazolium fluorochromate (IFC) oxidation of 11 meta- and para-substituted benzylamines, in varying mole fractions of benzene/2-methylpropan-2-ol binary mixtures, is first order in IFC and acid and zero order in substrate. The Hammett correlation yielded a U-shaped curve, indicating a change in the relative importance of bond formation and bond fission in the transition state. The rate data failed to correlate with macroscopic solvent parameters such as ,r and E. The correlation of kobs with Kamlet,Taft solvatochromic parameters suggests that H-bonding between the reacting species and the solvent plays a major role in governing the reactivity. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 159,167, 2010 [source] Solvent hydrogen bonding and structural effects on nucleophilic substitution reactions: Part 3.INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2007Reaction of benzenesulfonyl chloride with anilines in benzene/propan-2-ol mixtures Substitution reactions of 13 para- and meta-substituted anilines with benzenesulfonyl chloride in varying mole fractions of benzene in propan-2-ol have been investigated conductometrically. The second-order rate constants correlate well with pKa values of anilines and with the Hammett's equation. The negative Hammett reaction constant indicates the formation of an electron-deficient transition state. The rate data correlate satisfactorily with macroscopic solvent parameters such as relative permittivity, ,r, and polarity, ETN. Correlation of rate data with Kamlet,Taft solvatochromic parameters (,, ,, ,*) suggests that both the specific and nonspecific solute,solvent interactions influence the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 657,663, 2007 [source] Correlation analysis of reactivity in the oxidation of anilines by nicotinium dichromate in nonaqueous mediaINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2006D. S. Bhuvaneshwari The kinetics of oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate (NDC) in different organic solvent media in the presence of p -toluenesulfonic acid (TsOH) has been investigated. The rate of the reaction is zero order with respect to substrate, first order in NDC, and is found to increase with increase in [TsOH]. The various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species-anilines reaction (k2) correlates with Hammett's substituent constants affording negative reaction constants. The effect of para- and meta-substituents on the oxidation rates confirms to Swain et al.'s substituent constants F and R, both with negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ,r and E while showing satisfactory correlation with Kamlet,Taft's solvatochromic parameters (,, ,, and ,*). © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 657,665, 2006 [source] Studies on the kinetics of imidazolium fluorochromate oxidation of some meta - and para -substituted anilines in nonaqueous mediaINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2006D. S. Bhuvaneshwari The imidazolium fluorochromate (IFC) oxidation of meta - and para -substituted anilines, in seven organic solvents, in the presence of p -toluenesulfonic acid (TsOH) is first order in IFC and TsOH and is zero order with respect to substrate. The IFC oxidation of 15 meta - and para -substituted anilines at 299,322 K complies with the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental range. The specific rate of oxidizing species-anilines reaction (k2) correlates with substituent constants affording negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ,r and ENT. A correlation of rate data with Kamlet,Taft solvatochromic parameters (,, ,, ,*) suggests that the specific solute,solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute,solvent complexation. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 166,175, 2006 [source] Oxidation of substituted benzaldehydes by quinolinium chlorochromate: A structure and solvent dependent kinetic studyINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2003G. Fatima Jeyanthi The kinetics of oxidation of several para-substituted benzaldehydes by quinolinium chlorochromate was studied under pseudo-first-order conditions in different (hydrogen bond donor and hydrogen bond acceptor) neat organic solvents. The operation of nonspecific and specific solvent,solvent,solute interactions was explored by correlating the rate data with solvent parameters through correlation analysis. Both electron-releasing and electron-withdrawing substituents enhanced the rate and the Hammett plot showed a break in the reactivity order indicating applicability of dual mechanism. An explanation in conformity with structure and solvent effects on reactivity has been proposed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 154,158, 2003 [source] Solvent and structural effects on the oxidation of 2,6-diphenyl-piperidin-4-ones by quinolinium chlorochromateINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2002S. Saravana Kanna The kinetics of oxidation of 3-R-2,6-diphenyl-piperidin-4-ones (where R = H, Me, Et, and i -Pr) by quinolinium chlorochromate has been studied under pseudo-first-order conditions in different pure (protic and aprotic) solvents. The rate data is correlated with different solvent parameters using linear multiple regression analysis. From the regression coefficients, information on the solvent,reactant and the solvent,transition state interactions is obtained and the solvation models are proposed. Reasons for the difference in reactivity with structure are also discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 585,588, 2002 [source] Solvent effects on chemical processes: new solvents designed on the basis of the molecular,microscopic properties of (molecular solvent,+,1,3-dialkylimidazolium) binary mixturesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2008P. M. Mancini Abstract The purpose of this work was to analyze the microscopic feature of binary solvent systems formed by a molecular solvent (acetonitrile or dimethylformamide or methanol) and an ionic liquid (IL) cosolvent [1-(1-butyl)-3-methylimidazolium tetrafluoroborate or 1-(1-butyl)-3-methylimidazolium hexafluorophosphate]. The empirical solvatochromic solvent parameters ET(30), ,*, ,, and , were determined from the solvatochromic shifts of adequate indicators. The behavior of the solvent systems was analyzed according to their deviation from ideality. The study focused on the identification of solvent mixtures with relevant solvating properties in order to select mixed solvents with particular characteristics. The comparison of the molecular,microscopic solvent parameters corresponding to the selected binary mixtures with both ILs considered at similar mixed-solvent composition revealed that the difference is centered on the basic character of them. A kinetic study of a nucleophilic aromatic substitution reaction between 1-fluoro-2,4-dinitrobenzene (FDNB) and 1-butylamine (BU) developed in (acetonitrile or dimethylformamide,+,IL) solvent mixtures is presented in order to investigate and compare the solvent effects on a chemical process. For the explored reactive systems the solvation behavior is dominated by both the dipolarity/polarizability and the basicity of the media, contributing these solvent properties to accelerating the chemical process. Copyright © 2007 John Wiley & Sons, Ltd. [source] Synthesis, properties, and solvatochromism of 1,3-dimethyl-5-{(thien-2-yl)-[4-(1-piperidyl) phenyl]methylidene}-(1H,3H)-pyrimidine-2,4,6-trioneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2007Mohamed El-Sayed Abstract A new merocyanine dye, 1,3-Dimethyl-5-{(thien-2-yl)-[4-(1-piperidyl)phenyl]methylidene}- (1H, 3H)-pyrimidine-2,4,6-trione 3, has been synthesized by condensation of 2-[4-(piperidyl)benzoyl]thiophene 1 with N,N, -dimethyl barbituric acid 2. The solvatochromic response of 3 dissolved in 26 solvents of different polarity has been measured. The solvent-dependent long-wavelength UV/Vis spectroscopic absorption maxima, vmax, are analyzed using the empirical Kamlet,Taft solvent parameters ,* (dipolarity/polarizability), , (hydrogen-bond donating capacity), and , (hydrogen-bond accepting ability) in terms of the well-established linear solvation energy relationship (LSER): (1) The solvent independent coefficients s, a, and b and (vmax)0 have been determined. The McRae equation and the empirical solvent polarity index, ET(30) have been also used to study the solvatochromism of 3. Copyright © 2007 John Wiley & Sons, Ltd. [source] Solvatochromism of carbenium,arene EDA (electrondonor,acceptor) complexes and their behaviour on silicaJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2001Stefan Spange Abstract Spectral characteristics of two different types of electron donor,acceptor (EDA) complexes with charged components (arene,carbenium and anion,, acceptor) are presented. The UV,Vis absorption maxima of the charge-transfer (CT) band (,max,CT) of the EDA complexes were measured in various solvents and after adsorption on silica. Tropylium, triarylmethylium and diarylmethylium ions in combination with aromatic , donors, e.g. pyrene, acenaphthene and methoxy-substituted benzene derivatives and also the tetraethylammonium iodide,1,3,5-trinitrobenzene complex have been investigated by means of a special UV,Vis technique in transparent slurries of silica nanoparticles in 1,2-dichloroethane. Multiple linear regression analyses of the ,max,CT values of the EDA complexes in various solvents and on silica with the Kamlet,Taft solvent parameters and structure,reactivity terms of the complex components, e.g. the oxidation potential of the arene component or the Hammett substituent constant, ,p+, of the arylmethyl component, show their related properties to the solution complexes. The influence of the electron-pair donating capacity of a solvent on ,max,CT of carbenium/arene complexes was compared with the property of the silica surface in order to link EDA complexes. For the diarylmethyl carbenium ion,pyrene complexes on silica, the presence of a ,-like structure is discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] A robust bulk-solvent correction and anisotropic scaling procedureACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2005Pavel V. Afonine A reliable method for the determination of bulk-solvent model parameters and an overall anisotropic scale factor is of increasing importance as structure determination becomes more automated. Current protocols require the manual inspection of refinement results in order to detect errors in the calculation of these parameters. Here, a robust method for determining bulk-solvent and anisotropic scaling parameters in macromolecular refinement is described. The implementation of a maximum-likelihood target function for determining the same parameters is also discussed. The formulas and corresponding derivatives of the likelihood function with respect to the solvent parameters and the components of anisotropic scale matrix are presented. These algorithms are implemented in the CCTBX bulk-solvent correction and scaling module. [source] Flat bulk-solvent model: obtaining optimal parametersACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2002Andrei Fokine A bulk-solvent correction is regularly used for macromolecular refinement. The flat model of the bulk solvent is considered to be the most reliable. It is shown that the standard procedure does not always result in the optimal values of the bulk-solvent correction parameters. A method to obtain the best values for parameters ksol and Bsol of the flat-solvent model is discussed. The values of correctly determined parameters for crystallographic structures deposited in the Protein Data Bank are clustered around ksol = 0.35,e,Å,3 and Bsol = 46,Å2, which have a reasonable physical meaning. Such a distribution allows the use of these mean values of solvent parameters for many practical applications when refined parameters cannot be obtained, especially when an atomic model in the unit cell is not yet known. [source] | ||||||||||