Showing papers on "Solvent effects published in 1979"

Solution Chemistry of Surfactants

Abstract: of Volume 1.- I. General Overview Papers.- Ionic Interaction and Phase Stability.- Comparative Effects of Chemical Structure and Environment on the Adsorption of Surfactants at the L/A Interface and on Micellization.- Studies of Lyotropic Liquid Crystals that Align in Magnetic Fields.- Use of Surfactant and Micellar Systems in Analytical Chemistry.- Micellar Systems Studied by Positron Annihilation Techniques.- Solubilization in Aqueous Micellar Systems.- Nonionic Surfactant Micelles and Mixed Micelles with Phospholipids.- Commercial Surfactants: An Overview.- II. Thermodynamics and Kinetics of Micellization in Aqueous Media.- Direct Measurements of the Thermodynamic Properties of Surfactants.- Electrolyte Effect on Micellization.- Kinetics of Micellization.- Thermodynamics of Micelle Formation: Model Calculations for Sodium Octanoate.- Pre-Micellar Maximum in the Light Scattering from Cetyltrimethylammonium Bromide and Chloride.- Relaxation Amplitude of Non-Ionic Micelle Systems Perturbed by Solvent-Jump.- Mixed Micelle Solutions.- Anomalous Behaviour of Aromatic Alcohols on the Critical Micelle Concentrations of Cationic Surfactants.- Some Observations on the Micellar Behavior of Surfactants in Water and Aqueous Solvents.- Investigation of Aggregation Phenomena in Aqueous Sodium Dodecyl Sulfate Solutions at High NaCl Concentration by Quasielastic Light Scattering.- The Effect of Dissolved Oils and Alcohols on the CMC of Synthetic and Petroleum Sulfonates.- Application of Keto-Enol Tautomerism to the Study of Micellar Property of Surfactants.- III. Effect of Solvent and Micelles in Nonaqueous Media.- Solvent Effects on Amphiphilic Aggregation.- Association Behavior of Synthetic and Naturally Occurring Surfactants in Nonaqueous Solvents.- Ultrasonic Absorption Studies of Solutions of Ionic Amphiphiles in Organic Solvents.- Formation of Micelles of Cetyltrimethylammonium Bromide in Water-Dimethyl Sulfoxide Solutions.- Temperature Effect on Molecular Dynamics in Micellar System. Proton Spin-Lattice Relaxation Study of Cetyltrimethylammonium Bromide in Water-Dimethylsulfoxide Mixtures.- About the Contributors.

Solvent Effects in Organic Chemistry

Abstract: Intermolecular forceds, interactions between solute and solvent. Solvation. Classification of solvents. Chemical action of solvents: effects on equilibria and reactions. Effects on absorption spectra of organic compounds. Empirical parameters of solvent polarity. Toxicity, table of threshold values, tl and mak. -- ICCROM

Empirical Parameters of Solvent Polarity as Linear Free‐Energy Relationships

Abstract: Although the effect of solvent on the rate and the position of equilibrium of chemical reactions has been known since the last century, there are still no reliable and exact methods for a quantitative description and prediction of such solvent effects. Empirical parameters of solvent polarity are of great value in this respect and can be derived with the aid of the principle of “linear relationships between free energies” (LFE relationships). The present article deals with the possibilities of establishing reaction and absorption series using solvent-dependent standard reactions or standard absorptions of organic compounds. Particular attention is merited by the summary of the 24 most important empirical parameters of solvent polarity and the table of ET(30) values for 151 solvents. In addition to examples of the application of these values, attempts to improve the LFE correlations of singular empirical parameters of solvent polarity with the aid of multiparametric equations are described.

A molecular dynamics and Monte Carlo study of solvent effects on the conformational equilibrium of n‐butane in CCl4a),b)

Abstract: We report on a computer simulation study of the gauche–trans conformational equilibrium of n‐butane in liquid carbon tetrachloride solvent. The study is made possible by implementing an exact statistical mechanical theorem which relates the full intramolecular distribution function for a butane molecule to that of a hypothetical species which does not possess a large potential barrier separating the trans and gauche states. In addition to determining the trans–gauche equilibrium constant, the potential of mean torsion, that is, the reversible work required to alter the conformation is determined as a function of the dihedral angle. Recent theoretical work is compared with these computer experiments, and while qualitative agreement is found, the approximate theory overestimates the solvent effect. Finally, the change in solvent structure in response to a conformational change in the solute is determined.

Linear solvation energy relationships. Part 3. Some reinterpretations of solvent effects based on correlations with solvent π* and α values

Abstract: Solvent polarity and hydrogen bonding effects on a number of physical and chemical properties and reaction parameters are unravelled and rationalized by means of the solvatochromic comparison method and equations of the form XYZ=XYZ0+sπ*+aα, where π* is a measure of solvent polarity and α a measure of solvent hydrogen bond donor acidity. XYZ's considered include ET values for eight electronic spectral transitions, two sets of nitrogen hyperfine splitting constants, a set of fluorescence lifetimes, logarithms of rate constants for four nucleophilic substitution reactions, and the ‘electrophilicity parameter,’E, of Koppel and Palm.

A semiempirical model for the description of solvent effects on chemical reactions

Abstract: — An attempt is made to provide a more rigorous basis for the description of solvent effects on chemical reactions by taking into account the various free energy contributions involved in the transfer of a substrate from the gas to the solution phase. It is shown that the solvent influence on various chemical and physical processes can be represented in a semiquantitative or even quantitative way by means of three parameters, namely the socalled acceptor number, which represents a measure of the electrophilic or acceptor properties of the solvent, the donor number, which represents a measure of the nucleophilic or donor properties of the solvent and the standard free energy of vaporization of the solvent which is related to the free energy required to create holes in the solvent in which the substrates can be accomodated. Protic solvents usually do not obey the relationships obtained for aprotic media and this appears to be due to the varying basicity of the substrates under consideration.

The solvent effect on di‐tert‐butyl nitroxide. A dipole–dipole model for polar solutes in polar solvents

Abstract: New measurements of the solvent effect on the nitrogen hyperfine coupling constant of di‐tert‐butyl nitroxide are reported. These, together with literature data, are used to test various models for the solvent effect. At the Huckel level of approximation, aN is a linear function of the applied electric field. Thus various reaction field theories may be considered. The widely used Onsager reaction field does not account for the effects of the more polar solvents or for the differences between polar and nonpolar solvents. The Wertheim and Block–Walker reaction fields are better, especially for very polar solvents. However none of these continuum reaction fields is entirely satisfactory theoretically or experimentally. We propose a dipole–dipole model for polar solvents which is superior to the continuum models. From the dipole–dipole model, we suggest that the quantity μρ/M is a convenient linear parameter for polar solvent effects, the factors being solvent dipole moment, density, and molecular weight. The...

An interpretation of a general scale of solvent polarities. A simplified reaction field theory modification

Abstract: The existence of linear relationships of good quality involving the effects of polar solvents on different properties of neutral, highly polar solutes is rationalized in terms of the reaction field theory. It is shown that the treatment of Block and Walker in which the dielectric constant at a distance r from the center of the solute cavity is taken as t(r) = where en is the bulk dielectric constant, gives a satisfactory description of experimental results involving NMR shift data, solvation free energies, activation free energies, T-T* transitions, and molecular dipole moments. It is concluded that (1) the short-lived clustering of polar solvent molecules around dipolar solutes is a significant factor to be considered in the study of solvent effects on dipolar solutes; (2) the scope of the reaction field formalism can be extended to solutes of high polarity provided allowance is made for dielectric saturation of the polar solvent molecules.

Linear solvation energy relationships. Part 4. Correlations with and limitations of the α scale of solvent hydrogen bond donor acidities

Abstract: The solvatochromic comparison method is employed to amend and expand the data base for the α scale of solvent HBD (hydrogen bond donor) acidities. In combination with the π* scale of solvent polarities, the α scale serves to rationalize solvent effects on a number of chemical properties and reaction parameters (XYZs) through equations of the form, XYZ=XYZ0+sπ*+aα. Properties considered include electronic spectral data, free energies of transfer between solvents, 19F and 31P n.m.r. shifts, and log reaction rate constants. It is shown that Dimroth's ET(30) and Kosower's Z scales, intended as measures of solvent polarity (i.e.π*-equivalent), and Gutmann's ‘Acceptor Number (AN)’ scale, intended as a measure of solvent electrophilicity (i.e.α-equivalent), correspond in fact to linear combinations of π* and α.

Variable-temperature magnetic-susceptibility measurements of spin equilibria for iron(III) dithiocarbamates in solution

Abstract: The magnetic moments of four tris(NN-disubstituted dithiocarbamato)iron(III) complexes have been measured in solution over a wide temperature range, using an nmr method The assumption of a simple Boltzmann distribution between high- and low-spin forms (6A1 and 2T2) gives a good fit to the observed susceptibility data ΔS is approximately constant at ca 20 J K–1 mol–1 Solvent effects are small and there is no evidence that hydrogen bonding to chloroform is important in solution The paramagnetic shifts in the 1H nmr spectrum of one complex as a function of temperature have been analysed and give thermodynamic parameters in good agreement with those obtained from the susceptibility measurements

A statistical mechanical theory for activity coefficients of a dilute solute in a binary solvent

Abstract: A statistical mechanical calculation of the activity coefficients of a dilute solute,C, in a binary solvent,A-B, was made using a model for the interactions of a coordination cluster consisting of a solute atom and its neighboring solvent atoms. The derived equations are applicable to a variety of types of ternary solutions including substitutional and interstitial alloys as well as additive and reciprocal molten salts. The theory takes into account the interactions between solute and solvent atoms (ions) as well as changes in interactions of the solvent atoms (ions) which are neighbors of solute atoms (ions). Prior theories such as those of Wagner and the quasi-chemical theories of Alcock and Richardson and Jacob and Alcock can all be shown to be special cases of the present theory. The dependence of the activity coefficients of a solute on the solvent composition is calculated from a knowledge of the activity coefficients of the solvent components, solute activity coefficients in the two pure solvent components, a coordination number, a geometric factor which depends upon the type of solution, and a term which represents the nonadditivity of pair bond interactions within the cluster of a solute atom (ion) and its neighboring solvent atoms (ions). In the model, the thermodynamic properties of the solute are related to the relative concentrations of the different coordination clusters as well as to the thermodynamic properties of the solvent.

Linear solvation energy relationships. Part 1. Solvent polarity–polarizability effects on infrared spectra

Abstract: The linear solvation energy relationship (LSER) concept is shown to apply to i.r. spectra. Solvatochromic shifts of a variety of X = O, C–Cl, and O–H ⋯ B stretching frequencies and solvent effects on absorption intensities are linear with solvent π*-values. Values of s in the solvatochromic equation, ν=ν0+sπ*, are related to chromophore structures.

Solvent effect on radical polymerization of vinyl acetate.

Abstract: Absolute rate constants of vinyl acetate (VAC) polymerization have been measured by using the intermittent illumination method in various aromatic solvents and ethyl acetate at 30°. It was shown that the solvent effect was mainly ascribed to the variation in propagation rate constants (kp) with solvents rather than that in termination rate constants (kt). The kp increased in the order: benzonitrile < ethyl benzoate < anisole < chlorobenzene < fluorobenzene < benzene < ethyl acetate. This order is almost the same as that for vinyl benzoate (VBZ) previously reported. There was about an eightyfold difference between the largest and the smallest values. This large variation in kp is explained neither by copolymerization through solvents nor the chain transfer to solvents, but by a reversible complex formation between the propagating radical and aromatic solvents. The kp was determined in mixed solvents of ethyl benzoate and ethyl acetate, decreasing with increasing content of ethyl benzoate. This result supports the idea of a reversible complex. The stability constants (Ks) of the complex were estimated on the assumption that the complexed radical was in a dormant state and inactive in the polymerization. The correlation between Ks or kp and the calculated delocalization stabilization energy for the complex was found, and supported the explanation for the solvent effect.

Solvent effects on initial states and transition states for reactions of inorganic complexes

Abstract: The use of solvent effects on reactivities in the diagnosis of inorganic substitution mechanisms is discussed, and the converse approach, the use of reactions of known mechanism to.probe solvent structural properties, mentioned. Solvent effects on reactivity trends can be analysed into initial state and transition state compOnents by the use of appropriate thermOdynamic parameters for the reactant(s). Such an analysis has been carried out for a varietyof substitutions at inorganic centres, for example cobalt(III), iron(Ii), and platinum(II), and for peroxodisulphate oxidation of iron(II) species.

Radical Copolymerization of Acrylic Monomers. II Effect of Solvent on Radical Copolymerization of Methyl Methacrylate and Styrene

Abstract: The influence of various solvents on the copolymerization behavior of methyl methacrylate with styrene has been investigated. In these systems there is a significant solvent effect on both rS and rM which may be attributed to changes in the dielectric constant of the solvents used. The calculated relative reactivity of the polystyryl radical towards the methyl methacrylate monomer increases with increasing solvent polarity, whereas the reactivity of poly(methyl methacrylate) radical towards styrene monomer decreases. The results obtained are discussed taking into account the behavior of both monomers in homopolymerization with the same experimental conditions as in copolymerization.

The effect of dielectric constant upon the 1 J CH spin coupling constants in organic compounds

Abstract: A theoretical study is presented of the effects of solvent molecules on directly-bonded 13C-H nuclear spin-spin coupling constants (1 J CH) of acrylonitrile, dichloromethane, chloroform, difluoromethane and trifluoromethane. The solvent-solute interaction is estimated using Klopman's solvaton theory. Calculations of 1 J CH's are performed by the finite perturbation theory in the INDO approximation for acrylonitrile, difluoromethane and trifluoromethane, and in the CNDO/2 approximation for dichloromethane and chloroform. Calculated results are compared with the observed solvent effects.