Showing papers on "Solvent effects published in 1975"
TL;DR: In this article, a quantum-mechanical reaction field theory of solvent effects is proposed, which leads to an effective, non-linear, hamiltonian for the molecule in solution and hence to a tool for studying changes in charge distributions and molecular properties.
Abstract: A quantum-mechanical reaction field theory of solvent effects is proposed. It contains as a limiting case Onsager's model. It leads to an effective, non-linear, hamiltonian for the molecule in solution and hence to a tool for studying changes in charge distributions and molecular properties. Numerical examples are given.
476 citations
219 citations
178 citations
TL;DR: In this paper, a dynamic equation for the distribution coefficient is proposed that accounts for different solute-phase interactions in liquid chromatography, and the effect of solvent composition on retention is shown to be dependent on the probability of solute solvent interaction and thus the concentration of polar solvent in the mobile phase.
98 citations
52 citations
TL;DR: In this paper, a previously described empirical model for solvent effects is applied to kinetic, thermodynamic and spectroscopic data selected to reflect variation in solute-solvent interactions of a dipole-dipole character.
Abstract: A previously described empirical model for solvent effects is applied to kinetic, thermodynamic and spectroscopic data selected to reflect variation in solute-solvent interactions of a dipole-dipole character. The three parameter fit was found to describe the solvent effect successfully in 75% of the cases considered. The choice of basicity parameters for protic solvents is discussed, and the basicity scales of Gutmann, Kagiya, Koppel and Palm, and Arnett, are compared. It is concluded that an extension of the present model should take into consideration entropic effects associated with solute-solvent interactions.
48 citations
TL;DR: The results obtained under these conditions of solvents and temperature are consistent with the presence at the active site of the enzyme of a histidine residue, and thus provide a direct verification of the method of Findlay et al.
46 citations
TL;DR: In this article, the results were more in accord with the frontier orbital model of reactivity in the Diels-Alder reaction than with a standard linear free-energy approach.
Abstract: The kinetics and activation parameters for the series of 4-substituted (R) 1,2,4-triazoline-3,5-diones (R = Me, Et, But, CH2Ph, Ph, p-MeOC6H4, p-NO2C6H4, or N:CHPh) have been measured for the Diels–Alder reactions with diphenylbutadiene, anthracene, hexachlorocyclopentadiene, and bicyclo[2.2.1]heptadiene. The reactions have been studied in benzene, dioxan, and ethyl acetate. The results are more in accord with the frontier orbital model of reactivity in the Diels–Alder reaction than with a standard linear free-energy approach.
44 citations
TL;DR: In this article, a solvent and/or environmental effect has been introduced into the MO CNDO/2 calculation of a model hydrogen-bonded system, which is related to both the macroscopic dielectric properties of the solvent and to the local order (if any) around the solute.
43 citations
39 citations
TL;DR: The relation between solvent induced shifts of the 36 GHz microwave transition of quinoxaline in a hydrocarbon glass at 42 K and corresponding shifts in the phosphorescence 0-0 band was determined in this article.
TL;DR: The reaction of 2,6-dibromocyclohexanone (1) with morpholine gives 1-cyclopentenecarboxymorpholide (2) and 2-morpholino-2-cyclohexenone (3) as discussed by the authors.
Abstract: The reaction of 2,6-dibromocyclohexanone (1)with morpholine gives 1-cyclopentenecarboxymorpholide (2) and 2-morpholino-2-cyclohexenone (3) . The ratio of 2 :3 is remarkably affected by the reaction solvent, and the amide 2 or the enaminoketone 3 is obtained selectively when chloroform or HMPA was used, respectively.
TL;DR: In this article, the reactivity ratios for the free radical copolymerization of styrene and methyl methacrylate at 50°C have been evaluated in dioxane, acetone and dimethylformamide solutions.
TL;DR: In this paper, a series of natural bidentate α-amino acids substituted at the nitrogen atom with methyl and benzyl groups in different proportions have been studied in the copper(II) bis-complexes of N-benzylproline with N,N-dimethylvaline.
TL;DR: In this paper, the Koenigs-Knorr reaction of D -glucosyl chlorides having a non-participating group at C-2, using silver perchlorate as principal catalyst, was investigated.
TL;DR: In this paper, a general formalism for the solute and solvent effect on chemical equilibrium is developed, based on a simplified version of a result due to Kirkwood and Buff, and a specific example is worked out in some detail to detect the nature of the various factors that combine to induce a shift of the equilibrium in one direction or another.
Abstract: Using a simplified version of a result due to Kirkwood and Buff, a general formalism is developed for the solute and solvent effect on chemical equilibrium. A specific example—an association reaction—is worked out in some detail to detect the nature of the various factors that combine to induce a shift of the equilibrium in one direction or another.
TL;DR: In this article, a titration method utilizing glass electrodes and silver-silver chloride electrodes in a cell without liquid junction was used to determine the acidic dissociation constants at 15, 25, and 35°C of nine protonated nitrogen bases in mixtures of water and dimethyl sulfoxide (DMSO).
Abstract: A titration method utilizing glass electrodes and silver-silver chloride electrodes in a cell without liquid junction has been used to determine the acidic dissociation constants at 15, 25, and 35°C of nine protonated nitrogen bases in mixtures of water and dimethyl sulfoxide (DMSO). The mole fraction of DMSO in the mixed solvents was 0.2, 0.4, 0.6, and 0.8. The cell was calibrated with HCl (molality=0.01 mole-kg−1) in the mixed solvents, and the ionic strength and chloride molality remained substantially unchanged during the titration with added base. This method minimizes the errors resulting from the formation of AgCl
2
−
in the media rich in DMSO. The pK
a of all the protonated bases passes through a minimum at a solvent composition close to that at which H2O-DMSO mixtures display a maximum solvent structure. The results are discussed in terms of the preferential solvation of ions by the two types of solvent molecules. They are consistent with the hypothesis that increased solvent structure is accompanied by increased desolvation of the cation acids.
TL;DR: It was found that the thermally induced transition between form I and II under vacuum occurs with the pyrrolidine rings remaining in the down conformation, and the calculated values of s suggest that form I is more stable than form II in the regular down chain, while form II is morestable than form I in theregular up chain under vacuum at room temperature.
Abstract: Phenomenological theories of the form I in equilibrium to form II interconversion in poly(L-proline) have been presented by Schwarz (using the parameters s, sigma, beta', and beta'' in a 2 X 2 matrix formulation) and by the present authors (using the parameters s, sigma, betaC, and betaN in a 4 X 4 matrix formulation). In addition, a molecular theory was developed to compute s, sigma, beta', and beta'' under vacuum. In this paper, we take into account the effect of solvent on the parameters s, sigma, beta', and beta'' of the isothermal poly(L-proline) form I in equilibrium to form II interconversion. The growth parameter is sensitive to the binding of solvent molecules to the peptide CO groups, but the nucleation parameters sigma, beta', and beta'' are not affected by this type of solvent effect. The calculated values of s and sigma under vacuum are in good agreement with the corresponding values derived from experimental data. By combining the theoretical values of s, sigma, beta', and beta'' under vacuum with experimentally determined equilibrium constants for the binding of alcohols to the peptide CO groups (which differ in magnitude for form I and form II), it was possible to reproduce the experimental tranistion curves satisfactorily. Alternatively, the binding constants for alcohols, obtained by combining our theoretically computed parameters under vacuum with experimental equilibrium transition curves, are in a satisfactory agreement with those evaluated independently by infrared spectral measurements of the binding of alcohols to the peptide CO groups. It is pointed out that significant errors may arise in analyzing experimental data if short chains are included with long chains in the determination of s, sigma, beta', and beta'' from the equilibrium transition curves. The transition of poly(L-proline) from form II to form I when n-butyl alcohol is added to a solution of the polymer in benzyl alcohol is brought about by the slight difference in the binding free energies of both alcohols to the carbonyl groups of form II. The different binding affinities of two alcohols, ROH, to form II may arise from (a) the different hydrogen-bond strength between the alcohol and the proline carbonyl group, and (b) possible differences in nonbonded and electrostatic interactions between the R group and the binding-site environment of the proline carbonyl group. The greater binding affinity of form II (compared to form I) for given alcohol is attributed to the more open and extended conformation of form II.
TL;DR: In this article, it was shown that the methane gas-to-liquid shifts in eleven halo-methanes as solvents are indeed proportional to this squared function; −σm(CH4) = 9.62 (n22−1) 2/(2n22+1)2 ) where n2 is the refractive index of the solvent.
TL;DR: In this article, the beryllium ion was studied in water-methanol, water-ethanol and water-acetone mixtures, 0.2 mole fraction of an organic component being contained.
Abstract: Hydrolytic reactions of beryllium ion were studied in water-methanol, water-ethanol, and water-acetone mixtures, 0.2 mole fraction of an organic component being contained. In all the solutions containing 3M LiClO4 as an ionic medium at 25 °C, we found the Be2OH3+, Be2(OH)22+, Be3(OH)33+, and Be(OH)2 complexes. However, in a supplementary work in a 3M LiClO4 aqueous medium in which the solution had been equilibrated with precipitates of beryllium hydroxide and the supernatant was subjected to titration, we found Be6(OH)84+ instead of Be(OH)2. From a very slow equilibrium observed in the high pH region, we concluded that the Be(OH)2 complex formed by the addition of an alkaline solution gradually polymerizes to Be6(OH)84+ by releasing some OH− ions. Through these observations a critical survey is described for the species reported by various authors. The solvent effect on the formation constants of hydroxo complexes is also discussed.
TL;DR: In this paper, the first-order kinetics with respect to the concentration of polyphosphates were investigated in water and dioxane-water solvents at various pHs in the range from 3.0 to 11.0.
Abstract: The hydrolysis of long-chain polyphosphates (Graham’s salt) was carried out in water and dioxane-water solvents at various pHs in the range from 3.0 to 11.0 and at 30, 50, and 70 °C. The rates of the hydrolytic degradation of the polyphosphates into shorter chains and into trimetaphosphate obeyed the first-order kinetics with respect to the concentration of the polyphosphates. In acidic media, a small solvent effect was perceived on the rates of both the processes. On the other hand, in basic media the effect was very remarkable; that is, the rates of both the processes in the dioxane-water solvent were more rapid than in water. The results show that the rate of the hydrolysis of both the processes in basic media may be very dependent on the step of the nucleophilic attack of a water molecule on the phosphorus atom of phosphates, while in acidic media other factor, for example, the folding of the chains to a helix, may affect the overall rate. The activation energies for the two processes have been found ...
TL;DR: In this article, the ET-value for eight solvents at 25 °C over the pressure range 1-1,960 kg/cm2 was determined, and it was shown that there is a linear relationship between the pressure coefficient of ET and that of the logarithm of the rate constant of a Menschutkin reaction.
Abstract: The ET-value was determined for eight solvents at 25 °C over the pressure range 1–1,960 kg/cm2. They increase with pressure; the pressure dependence is affected by the nature of the solvents. It was also found that there is a linear relationship between the pressure coefficient of ET and that of the logarithm of the rate constant of a Menschutkin reaction: In k=a+bET On the basis of this relationship, an equation was derived in which the volume of activation ΔV\eweq is represented by the pressure coefficient of ET; the effect of solvents on ΔV\eweq is discussed by making use of this equation.
TL;DR: In this paper, the authors derived an equation giving the overall rate of copolymerization of styrene and methyl methacrylate in acetone, in dimethylformamide and in dioxan.
Abstract: The solution copolymerization of styrene and methyl methacrylate in acetone, in dimethylformamide and in dioxan has been interpreted on the basis of a proposed model which includes chain end mobility and chemical reactivity. For all systems the derived equation giving the overall rate of copolymerization is in agreement with the experimental data. The effect of the reaction medium on bimolecular termination can be represented by the dependence of the rate-conditioning segmental rearrangement on medium fluidity.There is a marked solvent effect on the propagation rate coefficients. It is more pronounced for styrene than for methyl methacrylate and it shows an opposite trend for the two monomers: compared to the value for bulk polymerization kp for styrene is decreased, whereas kp for methyl methacrylate is increased in solution.
TL;DR: In this article, the configurational behavior of an isolated terminally anchored chain molecule interacting with a surface has been investigated using a computational statistical technique, which involves the simulation of the canonical ensemble of the system by a method analogous to that of Metropolis et al. The model assumes a lattice model with a square-well potential function for the segment/segment and segment/surface interactions.
Abstract: The configurational behaviour of an isolated terminally “anchored” chain molecule interacting with a surface has been investigated using a computational statistical technique. The technique involves the simulation of the canonical ensemble of the system by a method analogous to that of Metropolis et al. The present study assumes a lattice model with a square-well potential function for the segment/segment and segment/surface interactions. The solvent effect is incorporated in the model through the segment/segment interactions: it is assumed that good solvents produce repulsions between the segments, while bad solvents lead to attraction. The bonds in the chain assume three conformational states, viz. trans, gauche+ and gauche–, with the trans/gauche conformational energy difference equal to 1 kT. It was found that in a good solvent the molecule exists in an extended state. The outstanding feature of the configuration is long “tail” protruding into the solution phase, and there is a lower tendency for the formation of “loops”. A bad solvent, on the other hand, renders the molecule coiled and promotes the formation of “loops”.
TL;DR: In this paper, photo-rearrangement reactions of acridine 10-oxides are discussed and compared with those of bicyclic and monocyclic azine N-oxide, e.g., quinoline 1-oxided and pyridine 1-oxide.
Abstract: Photolysis of a series of acridine 10-oxides (Ia-Ig) in various solvents is reported. The structures of photo-products were determined by syntheses, chemical transformation to the known compounds, or by direct examination of their spectroscopic data. Based on the structures of photo-products and the solvent effect on the product distribution in these photolyses, a mechanistic rationalization of these photo-reactions is presented. The characteristic features of the photo-rearrangement reactions of acridine 10-oxides are discussed and compared with those of bicyclic and monocyclic azine N-oxides, e, g., quinoline 1-oxides and pyridine 1-oxides.
TL;DR: The effects of ethanol, ethylene glycol, dioxane, and other organic co-solvents upon the hydrogen exchange rates of randomly coiled oxidizedRNase, native RNase, and native trypsin have been measured.