Copolymerization Behavior of Some Acidic and Basic Monomers

Copolymerization reactivity ratios of the systems 4-vinyl-pyridine (VP)-methacrylic acid (MA), dimethylamino methacrylate (DMAM)-MA, and VP-DMAM were obtained using the Fineman-Ross procedure. The experimental values were found to differ considerably from the values calculated from the Q-e scheme. R₁ and r₂ values calculated using seven different models for the VP-MA system have been compared with the experimental values.     

Prediction of Physical Properties of Dimethacrylate Polymer Networks by a Group Contribution Approach

In this work, the correlation between experimental and theoretical values of density (ρ) and glass transition temperature (T _g ) of dimethacrylate polymer networks is elaborated. The developed methodologies are based on the additive principle of the known monomer chemical structures. The predicted values of ρ differed by a maximum of 1% from the experimental values. The methodology developed for T _g prediction is based on the assumption that dimethacrylate structural units are treated as main chains between ?CH₂C(CH₃)? tri-functional volumeless cross-links. Three-quarters of the calculated T _g values differed less than 20 K from the experimental ones.     

Calculation of optimum geometries and force fields by the CNDO/force method

CNDO/Force calculations have been performed on a series of molecules, H₂CO, F₂CO, CF₄, CHF₃, CH₂F₂ and CH₃F. The optimum geometries and force fields are reported. It is found that the method can successfully predict the geometries of polyatomic molecules. The bending force constants and interaction force constants are, in general, comparable with experimental values both with respect to sign and magnitude. The stretching force constants have higher values than the experimental force constants. However, the trend in stretching force constants of a series of molecules is comparable with that of the corresponding experimental values.     

Theoretical Study of Firefly Luciferin pKa Values—Relative Absorption Intensity in Aqueous Solutions

Ground‐state vibrational analyses of firefly luciferin and its conjugate acids and bases are performed. The Gibbs free energies obtained from these analyses are used to estimate pK_a values for phenolic hydroxy and carboxy groups and the N–H⁺ bond in the N‐protonated thiazoline or benzothiazole ring of firefly luciferin. The theoretical pK_a values are corrected using the experimental values. The concentrations of these chemical species in solutions with different pH values are estimated from their corrected pK_a values, and the pH dependence of their relative absorption intensities is elucidated. With the results obtained we assign the experimental spectra unequivocally. Especially, the small peak near 400 nm at pH 1–2 in experimental absorption spectra is clarified to be due to the excitation of carboxylate anion with N‐protonated thiazoline ring of firefly luciferin. Our results show that the pK_a values of chemical species, which are contained in the aqueous solutions, are effective to assign experimental absorption spectra.     

Enthalpy Relaxation in Glasses: Regression analysis of integral DSC data

A new method of calculation of parameters of enthalpy relaxation models is proposed. Regression analysis treatment compares the experimental and calculated values of relaxation enthalpy. The experimental values of relaxation enthalpy are obtained by numerical integration of the difference between the two DSC curves. Contrary to the overall shape of the DSC curve the integral values are not affected by particular heat flow conditions during the DSC experiment. The Narayanaswamy's numerical model based on the Kohlrausch—William—Watts relaxation function was used to calculate the theoretical values of relaxation enthalpy. The application of the proposed method on the DSC experimental data of enthalpy relaxation of As₂Se₃ is shown.This revised version was published online in November 2005 with corrections to the Cover Date.     

Calculation of bond dissociation energies of diatomic molecules using bond function basis sets with counterpoise corrections

Bond function basis sets combined with the counterpoise procedure are used to calculate the molecular dissociation energies D_e of 24 diatomic molecules and ions. The calculated values of D_e are compared to those without bond functions and/or counterpoise corrections. The equilibrium bond lengths r_e and harmonic frequencies o_e are also calculated for a few selected molecules. The calculations at the fourth-order Møller-Plesset approximation (MP 4) have consistently recovered about 95–99% of the experimental values for D_e; compared to as low as 75% without use of bond functions. The calculated values of r_e are typically 0.01 Å larger than the experimental values, and the calculated values of o_e are over 95% of the experimental values. © 1996 John Wiley & Sons, Inc.     

Calculations of pKa values of carboxylic acids in aqueous solution using Möller-Plesset perturbation theory

The acidity constants of some carboxylic acids in aqueous solution have been calculated. The calculations were carried out using Möller-Plesset (MP) perturbation theory. The Polarizable Continuum Model (PCM) is used to describe the solvent. This model furnishes pK_a values that agree more closely with experimental data than those obtained at the level of Hartree-Fock (HF) and Density Functional Theory (DFT-B3LYP). The root-mean-square of errors of the calculated pK_a values are less than 1.0 for the studied acids. The molecules analyzed consist of acids with pK_a values in the range of 1.30 to 5.05, and have been partitioned into three classes. Class I includes acids with pK_a values higher than 4.00. Class II includes strong acids with pK_a values between 3.00 to 4.00. Class III includes very strong acids with pK_a values less than 3.00. The calculated pK_a values for the acids in Class I and Class II agree more closely with experimental values. The root-mean-square of errors for the Class I and Class II compounds are 0.70 and 0.78 pK_a units, respectively.     

The 2-Methoxyethanol + 1,2-Dimethoxyethane + Water Ternary System. Static Relative Permittivities from −10 To +80°C

Static relative permittivities of the 2-methoxyethanol + 1,2-dimethoxyethane + water ternary solvent system were measured as a function of temperature (-10 = t/°C = 80) and of composition, over the whole molar fractions range 0 = x₂, x₂, x₃ = 1. The experimental values have been used to test some empirical relationships accounting for the dependence of e on T, x_i, and on T, x_i couples of values. A comparison between calculated and experimental data shows that these relationships can be profitably employed to predict e values in correspondence to experimental data gaps. The excess dielectric permittivity, e^E, assumes, in the most cases, negative values for any compositions of the mixtures, while the values of the excess molar polarization, P^E, are positive. The large values of the excess quantities are indicative of the strong specific interactions among similar, as well as different molecules in the mixtures. Discussion of the data in terms of Kirkwood correlation factor also gives information on the short-range intermolecular interactions among the components, suggesting the formation of two-components adducts rather than of than more complex moieties involving all three molecular species.     

Chain transfer reactions in emulsion polymerization of butadiene/styrene

Calculation of regulating index r from M̄_W values determined by experiments is proposed. The calculation is based on the assumption that the M̄_W values only depend on the conversion and the regulating index in emulsion polymerization. On this basis the calculation of regulator concentration in the latex particles was also possible. M̄_W values calculated in this way and experimental M̄_W values show good agreement.     

What are the pKa values of organophosphorus compounds?

A first-principle theoretical protocol was developed, which could successfully predict the pK_a values of a number of amines and thiols in DMSO with a precision of about 1.1 pK_a unit. Using this protocol we calculated the pK_a values of diverse types of organophosphorus compounds in DMSO. The accuracy of these predicted values was estimated to be about 1.1 pK_a because phosphorus is in the same group as nitrogen and in the same period as sulfur. The theoretical predictions were also consistent with all the available experimental data. Thus, a scale of reliable pK_a values was constructed for the first time for organophosphorus. These pK_a values would be helpful to synthetic chemists who need to design the experimental conditions for handling deprotonated organophosphorus. On the basis of these pK_a values we also studied, for the first time, some interesting topics such as the substituent effects on the pK_a values of various types of organophosphorus, and the differences between the pK_a values of organophosphorus and organic amines.     

Activity coefficients at infinite dilution of organic solutes in the ionic liquid trihexyl(tetradecyl)phosphonium tetrafluoroborate using gas–liquid chromatography at T = (313.15, 333.15, 353.15, and 373.15) K

Activity coefficients at infinite dilution have been measured by gas–liquid chromatography for 27 organic solutes (n-alkanes, 1-alkenes, 1-alkynes, cycloalkanes, aromatics, alcohols, and ketones) in the ionic liquid trihexyl(tetradecyl)phosphonium tetrafluoroborate [3C₆C₁₄P][BF₄]. The measurements were carried out at four different temperatures viz. T = (313.15, 333.15, 353.15, and 373.15) K. From the experimental data, partial molar excess enthalpy values at infinite dilution were calculated for the experimental temperature range. The selectivity values for the separation of n-hexane/benzene, cyclohexane/benzene, and methanol/benzene mixtures were determined from the experimental infinite dilution activity coefficient values. These values were compared to those available in the literature for other ionic liquids and commercial solvents, so as to assess the feasibility of employing [3C₆C₁₄P][BF₄] in solvent-enhanced industrial separations.     

Anwendung des elektrostatischen Molekülmodells (RITTNER-Modells) auf Monohalogenide der Gruppen IIa,IIIa IVa und Ib

Newly calculated values of the dipol polarizabilities of singly charged metal ions are used in the calculation of the dissociation energy D₀ and of the anharmonicity constant ω_ex_e of group IIa, IIIa, IVa and Ib monohalides. Comparison with experimental values from literature suggests the empirical model as reasonable approximation.     

The effect of experimental methods and measurement conditions on values of the kinetic parameters of [Co(NH3)6]2(C2O4)3·4H2O

Using the thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O as a basis, the paper presents results which show how computed values of kinetic parameters are influenced by experimental conditions (ambient atmosphere, sample mass, linear heating rate) when using the non-isothermal methods and the Coats-Redfern (CR) modified equation. It also illustrates the influence of the experimental methods i.e. non-isothermal and isothermal (conventional) methods and also a quasiisothermal-isobaric one which can be recognised as equivalent to Constant Rate Thermal Analysis (CRTA). The results obtained have confirmed the significant influence of the experimental parameters as well as that of the experimental method used on the estimated values of kinetic parameters. The correlation between activation energy (E) and sample mass (m) or heating rate (β) is generally of a linear nature:E=a+bx     

Dependence of the reactivity of five-membered heterocycles on their structure. 3. Proton affinity of azoles and oxazoles

The proton affinity (PA) of a number of azoles and oxazoles was calculated by MNDO and STO-3G ab initio methods. In spite of the fact that these methods predict poorly the absolute values of the PA, a good correlation between the PA values calculated by STO-3G and the experimental values of PA as well as pK_a values exists. Correlation of the experimental values with MNDO results are much worse.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 508–511, April, 1989.     

Electrical surface resistivity of conductive polymers - A non-Gaussian approach for determination of confidence intervals

Polyanilines doped with different acids (HCl, H₂SO₄ and dodecylbenzenesulfonic acid, DBSA) were prepared and their surface electrical conductivities were characterized in a four-probe device, connected to a real-time data acquisition board. Collected data were synchronized and conductivity calculations were performed. The conductive behavior of the polyanilines was investigated along the electrification time. This allowed for introduction of a non-Gaussian technique for determination of the confidence intervals of surface resistivity data. It is shown that the distribution of experimental surface resistivity data does not follow a normal probability distribution function (PDF). Thus, ordinary assumptions related to normal distribution of the experimental errors are wrong and must be corrected for proper determination of the confidence limits of measured resistivity values. It is shown here that confidence limits of resistivity values are asymmetrical and that distribution of experimental values can follow multimodal distributions.     

A model for predicting the solubility of 1,3,5-trinitro-1,3,5-s-triazine (RDX) in supercritical CO2: isothermal–isobaric Monte Carlo simulations

Isothermal–isobaric Monte Carlo (NPT-MC) simulations and the Widom test particle method were used to predict the solubility of the explosive 1,3,5-trinitro-1,3,5-s-triazine (RDX) in supercritical CO₂. A Lennard–Jones potential energy function was chosen to describe the interaction between RDX and CO₂, and calibrated using two experimental solubility values. NPT-MC simulations using this interaction potential predicted solubilities of RDX in CO₂ over a temperature range of 308 to 353 K and pressures ranging from 10.4 to 48.3 MPa that were in good agreement with experimental values.     

Application of the porous-sphere hydrodynamic model to dilute polymer solutions

The porous-sphere model of Debye–Brinkman–Bueche is applied to predict the limiting frictional coefficient f₀ and intrinsic viscosity [η] of polystyrene fractions in tetrahydrofuran and random protein coils in 6M guanidine hydrochloride. Following the formulation of Wiegel and Mijnlieff, the molecular permeability is modeled to increase exponentially as the square of the distance from the center of the molecule. A method is developed to obtain this permeability from the translational diffusion coefficient. The experimental values of f₀ and [η] are in satisfactory agreement with the calculated values. Also, this analysis predicts values of the Mandelkern–Flory–Scheraga parameter for flexible coils which are significantly smaller than the minimum values permitted by the Kirkwood–Riseman theory. This is in accord with the experimental evidence.     

Une nouvelle méthode numérique de détermination parspectrophotométrie de constantes d'ionisation sechevauchant

A new method of calculation has been developed to obtain two pK_a values from spectrophotometric data in cases when the values are so close together that the calculations usually applied for individual pK_a values are not appropriate. This technique, in which all the experimental data are used to solve for absorbance of monoprotonated species, pK_a1 and pK_a7 by a “complex” method of optimization, is more general than the classical least-squares method. An application is described.     

288.15-318.15K温度范围内离子液体[C5mim][Pro]水溶液的体积和表面性质

在288.15-318.15 K温度范围内,测定了不同浓度离子液体1-戊基-3-甲基咪唑丙酸盐([C5mim][Pro])水溶液的密度和表面张力,计算了不同温度下不同浓度的溶液热膨胀系数、表观摩尔体积和溶液等张比容;根据密度实验数据计算得到溶质表观膨胀率,并与Harned和Owen提供的理论方程计算结果作了比较,两者计算结果能够很好一致;另外,本文还验证了预测溶液表面张力的经验方程,用其预测溶液的表面张力,不仅与溶液表面张力实验值在误差范围内很好一致,也与用等张比容方法预测的结果一致.