scholarly journals Quantum chemical approach to calculating the enthalpies of the formation of alkali metal xanthates

2020 ◽  
Vol 15 (2) ◽  
pp. 30-37
Author(s):  
Yu. V. Popov ◽  
A. S. Dolgachev ◽  
E. V. Shishkin ◽  
Yu. L. Zotov ◽  
V. E. Shishkin
Keyword(s):  
Experimental Data ◽  
Alkali Metal ◽  
Quantum Chemical ◽  
Linear Regression Analysis ◽  
Biologically Active ◽  
Enthalpies Of Formation ◽  
Regression Equations ◽  
Flotation Reagents ◽  
Organic Part ◽  
Semi Empirical

Objectives. The aim of this work is to study the possibility of the joint use of quantum chemical methods and correlation analysis to determine the formation enthalpies of metal-containing organic substances using the example of alkali metal xanthates, which are of interest as biologically active substances and effective flotation reagents. Methods. Semi-empirical methods of quantum chemical calculating (Modified Neglect of Diatomic Overlap, Austin Model 1, Recife model 1 methods) and linear regression analysis were used. Results. Using the semi-empirical Modified Neglect of Diatomic Overlap, Austin Model 1, and Recife model 1 methods, the enthalpies of formation of 16 potassium and sodium alkyl xanthates were calculated, and the obtained results were compared with experimental data. It was found that the best correlation for potassium and sodium salts of dithiocarbonic acid esters could be observed using the Austin Model 1 method. Using the obtained regression equations, the enthalpies of formation were calculated for 30 xanthates, the organic part of which contained alkyl, cyclic non-aromatic structures, and one or two heteroatoms such as nitrogen, oxygen, and fluorine, and for which there are no experimental data. Conclusions. As a result of the study, an excellent correlation was established between the experimental and the calculated (by the Austin Model 1 method) values of the enthalpies of formation of potassium and sodium alkyl xanthates. The data obtained can be used to calculate the thermal effect of the xanthogenation reactions of alcohols and to design the production of the corresponding xanthates. 

Анализ вычислительных и экспериментальных исследований переключения поляризации в ПВДФ и П (ВДФ-ТрФЭ) сегнетоэлектрических пленках на наноуровне

2015 ◽  
Vol 10 (2) ◽  
pp. 372-386 ◽  
Author(s):  
В.С. Быстров ◽  
V.S. Bystrov
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Electric Field ◽  
Quantum Chemical ◽  
Polyvinylidene Fluoride ◽  
Domain Switching ◽  
Polarization Switching ◽  
Molecular Structures ◽  
Switching Mechanism ◽  
Semi Empirical

In this paper, molecular models are used to investigate and analyze the polarization switching in the polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) Langmuir-Blodgett (LB) nanofilms, in comparison with the experimental data at the nanoscale. Quantum-mechanical calculations and modeling, as well as molecular dynamics (MD) simulations based on semi-empirical quantum-chemical methods (such as PM3), show that the energy of the studied PVDF and P (VDF-TrFE) molecular structures, and their polarization switching proceed by the intrinsic homogeneous switching mechanism in the framework of the phenomenological theory of Landau-Ginzburg-Devonshire (LGD) in the linear approximation at low values of the electric field. The magnitude of the resulting critical coercive field is within the EC ~ 0.5 ... 2.5 GV/m, which is consistent with experimental data. It is also found that the uniform polarization switching mechanism of the polymer chains PVDF and P (VDF-TrFE) is due to the quantum properties of the molecular orbitals of the electron subsystem. This is clearly seen in both the polarization hysteresis loops, and the total energy changes. In this case, the turnover chain time, obtained by molecular dynamics within semi-empirical quantum-chemical PM3 approach in a limited Hartree-Fock approximation, when approaching this critical point, increases sharply, tending to infinity, which corresponds to the theory of LGD. Otherwise, at the high values of the applied electric field the polarization switching correspond to the extrinsic domain mechanism in the frame of the microscopic Kolmogorov–Avrami–Ishibashi (KAI) theory, describing bulk ferroelectric crystals and thick films. The performed analysis of computational and experimental data allows us to estimate the critical sizes of the possible transition region approximately on the order of 10 nm between intrinsic homogeneous and extrinsic domain switching mechanisms.

scholarly journals Thermodynamic description of alkali metal hydroxides over a wide range of temperatures, pressures and densities of aqueous fluids

2019 ◽  
Vol 98 ◽  
pp. 05001 ◽  
Author(s):  
Nikolay Akinfiev
Keyword(s):  
Experimental Data ◽  
Thermodynamic Properties ◽  
Alkali Metal ◽  
Quantum Chemical ◽  
Dissociation Constants ◽  
Thermodynamic Description ◽  
Metal Hydroxides ◽  
Alkali Metal Hydroxides ◽  
Wide Range

All available experimental data on dissociation constants of aqueous hydroxides of Na, K, and Li were critically assembled and together with quantum chemical estimations used to evaluate parameters of the AD EoS [1] for corresponding aqueous molecules NaOH(aq), KOH(aq), and LiOH(aq). Use of the proposed approach allows proper prediction of the whole set of thermodynamic properties of these hydroxides over a wide range of temperatures (0 – 800 °C), pressures (0.1 – 800 MPa) and solvent densities (0.03 – 1.1 g·cm-3).

Simple theoretical models of elimination reactions on polar catalysts; Dehydration reactivity of secondary alcohols on acidic and basic catalysts

1985 ◽  
Vol 50 (4) ◽  
pp. 920-929 ◽  
Author(s):  
Jiří Sedláček
Keyword(s):  
Experimental Data ◽  
Quantum Chemical ◽  
Theoretical Models ◽  
Aliphatic Alcohols ◽  
Secondary Alcohols ◽  
Carbonium Ion ◽  
Dehydration Reactions ◽  
Aromatic Alcohols ◽  
Basic Catalysts ◽  
Simple Models

CNDO/2 calculations for simple models of adsorption and dehydration reactions of secondary aliphatic and aromatic alcohols on polar catalysts are presented. The models involve selected stages of elimination mechanisms of various types (E1, E2 and E1cB elimination). Calculated quantum chemical quantities were correlated with reported experimental data. It is shown that reactivities for the series of substituted phenylethanols correlate very well with the ease of carbonium ion formation. In the case of aliphatic alcohols, calculated quantities correlate generally with the reactivities on SiO2 and are in anticorrelation with the reactivities on Al2O3.NaOH.

Force field for in-plane vibrations of terephthalonitrile

1989 ◽  
Vol 54 (1) ◽  
pp. 18-27 ◽  
Author(s):  
Juan F. Arenas ◽  
Juan I. Marcos ◽  
Francisco J. Ramírez
Keyword(s):  
Experimental Data ◽  
Force Field ◽  
Normal Coordinates ◽  
Internal Coordinates ◽  
Isotopic Shifts ◽  
Quadratic Force Field ◽  
Semi Empirical

The general quadratic force field for the in-plane vibrations of terephthalonitrile was calculated by the semi-empirical MINDO/3 method. This force field was refined to the frequencies observed experimentally for terephthalonitrile and isotopic shifts of terephthalonitrile-[15N2]. The refined frequencies reproduce the experimental data with errors less than 0.5%. The normal coordinates and the force field in internal coordinates were also calculated from the refined field.

scholarly journals Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution

Symmetry ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 497
Author(s):  
Ewa D. Raczyńska
Keyword(s):  
Aqueous Solution ◽  
Quantum Chemical ◽  
Biologically Active ◽  
Deprotonation Reaction ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Scanty Information ◽  
Derivatives Of ◽  
Common Anion ◽  
Tautomeric Mixture

Keto-enol prototropic conversions for carbonyl compounds and phenols have been extensively studied, and many interesting review articles and even books appeared in the last 50 years. Quite a different situation takes place for derivatives of biologically active azulene, for which only scanty information on this phenomenon can be found in the literature. In this work, quantum-chemical studies have been undertaken for symmetrically and unsymmetrically substituted azulenols (constitutional isomers of naphthols). Stabilities of two enol (OH) rotamers and all possible keto (CH) tautomers have been analyzed in the gas phase {DFT(B3LYP)/6-311+G(d,p)} and also in aqueous solution {PCM(water)//DFT(B3LYP)/6-311+G(d,p)}. Contrary to naphthols, for which the keto forms can be neglected, at least one keto isomer (C1H, C2H, and/or C3H) contributes significantly to the tautomeric mixture of each azulenol to a higher degree in vacuo (non-polar environment) than in water (polar amphoteric solvent). The highest amounts of the CH forms have been found for 2- and 5-hydroxyazulenes, and the smallest ones for 1- and 6-hydroxy derivatives. The keto tautomer(s), together with the enol rotamers, can also participate in deprotonation reaction leading to a common anion and influence its acid-base properties. The strongest acidity in vacuo exhibits 6-hydroxyazulene, and the weakest one displays 1-hydroxyazulene, but all azulenols are stronger acids than phenol and naphthols. Bond length alternation in all DFT-optimized structures has been measured using the harmonic oscillator model of electron delocalization (HOMED) index. Generally, the HOMED values decrease for the keto tautomers, particularly for the ring containing the labile proton. Even for the keto tautomers possessing energetic parameters close to those of the enol isomers, the HOMED indices are low. However, some kind of parallelism exists for the keto forms between their relative energies and HOMEDs estimated for the entire molecules.

F-CENTER IMPACT ON PHOTOELECTROCHEMICAL PROPERTIES IN HEMATITE

2010 ◽  
Vol 24 (18) ◽  
pp. 1963-1970 ◽  
Author(s):  
ARVIDS STASHANS ◽  
RICHARD RIVERA
Keyword(s):  
Experimental Data ◽  
Optical Properties ◽  
Oxygen Vacancy ◽  
Quantum Chemical ◽  
Vacancy Defect ◽  
Chemical Model ◽  
Photoelectrochemical Properties ◽  
Structural And Optical Properties ◽  
F Center ◽  
Quantum Chemical Model

Structural and optical properties of F-center (two electrons trapped by an oxygen vacancy) defect in hematite have been studied using a quantum-chemical model. Calculated absorption energies, 0.9 eV and 3.6 eV, are discussed in terms of the available experimental data. An explanation for the origin of experimentally observed electron depletion in hematite is proposed.

A Critical Review of NOx Correlations for Gas Turbine Combustors

1975 ◽  
Author(s):  
D. A. Sullivan ◽  
P. A. Mas
Keyword(s):  
Experimental Data ◽  
Data Base ◽  
Gas Turbine ◽  
Critical Review ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Empirical Correlations ◽  
Gas Turbine Combustors ◽  
Semi Empirical ◽  
Adequate Data

The effect of inlet temperature, pressure, air flowrate and fuel-to-air ratio on NOx emissions from gas turbine combustors has received considerable attention in recent years. A number of semi-empirical and empirical correlations relating these variables to NOx emissions have appeared in the literature. They differ both in fundamental assumptions and in their predictions. In the present work, these simple NOx correlations are compared to each other and to experimental data. A review of existing experimental data shows that an adequate data base does not exist to evaluate properly the various NOx correlations. Recommendations are proposed to resolve this problem in the future.

scholarly journals CURVAS DE SECAGEM E AVALIAÇÃO DA ATIVIDADE DE ÁGUA DA BANANA PASSA

2004 ◽  
Vol 22 (1) ◽  
Author(s):  
MILTON CANO-CHAUCA ◽  
AFONSO M. RAMOS ◽  
PAULO C. STRINGHETA ◽  
JOSÉ ANTONIO MARQUES ◽  
POLLYANNA IBRAHIM SILVA
Keyword(s):  
Experimental Data ◽  
Linear Regression ◽  
Moisture Content ◽  
Water Activity ◽  
Linear Regression Analysis ◽  
Sorption Isotherms ◽  
Exponential Model ◽  
Drying Time ◽  
Non Linear ◽  
Drying Curves

Curvas de secagem de banana passa foram determinadas, utilizando-se três temperaturas do ar de secagem. Os resultados indicaram que para reduzir o teor de umidade do produto até 23,5% foram necessários tempos de secagem de 51, 36 e 30 horas paras as temperaturas de 50, 60 e 70ºC, respectivamente. O modelo exponencial U/Uo = exp(-kt) foi ajustado para os dados experimentais mediante análise de regressão não-linear, encontrandose alto coeficiente de regressão linear. Determinou-se a atividade de água do produto ao longo do processo de secagem para as três temperaturas testadas. Estudou-se a correlação entre a atividade de água e o teor de umidade do produto, determinando-se as isotermas de dessorção da banana passa a 25ºC. Observou-se que a atividade de água diminuiu em função do tempo de secagem e do teor de umidade para as três temperaturas de secagem. Os dados experimentais foram ajustados mediante regressão não-linear ao modelo polinomial e a seguinte equação foi obtida: U = -1844,93 + 7293,53Aa – 9515,52Aa2 + 4157,196Aa3. O ajuste mostrou-se satisfatório (R2 > 0,90). DRYING CURVES AND WATER ACTIVITY EVALUATION OF THE BANANA-PASSES Abstract Banana drying curves were determined by utilizing three drying air temperatures. The results indicated that to reduce the moisture content of the product until 23.5% it were necessary drying times of 51, 36 and 30 hours for temperatures of 50, 60 and 70ºC, respectively. The exponential model U/Uo = exp(-kt) was adjusted for the experimental data by means of non linear regression analysis, and a high coefficient of linear regression was found. The water activity of the product was determined throughout the drying process for the three tested temperatures. The correlation between the water activity and moisture content of the product was studied, and the sorption isotherms were determined at 25º C. It was observed that the water activity decreased in function to the drying time and moisture content for the three drying temperatures. The experimental data were adjusted by means of non linear regression to the polynomial model and the following equation was obtained: U = - 1844.93 + 7293.53A a – 9515.52 Aa 2 + 4157.196A a 3. The final adjust was satisfactory (R2 > 0.90).

scholarly journals An approach to determine enthalpies of formation for ternary compounds

2010 ◽  
Vol 46 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Y. Du ◽  
J. Wang ◽  
Y.F. Ouyang ◽  
L.J. Zhang ◽  
Z.H. Yuan ◽  
...  
Keyword(s):  
Experimental Data ◽  
First Principles ◽  
Integrated Approach ◽  
Enthalpies Of Formation ◽  
Calphad Approach ◽  
Miedema Model ◽  
Theoretical Computation ◽  
Ternary Compounds ◽  
Data Yield ◽  
Experimental Values

An integrated approach of experiment and theoretical computation to acquire enthalpies of formation for ternary compounds is described. The enthalpies of formation (DHf ) for Al71Fe19Si10 and Al31Mn6Ni2 are measured via a calorimeter. Miedema model, CALPHAD and first-principles method are employed to calculate DHf for the above compounds and several Al-based ternary compounds. It is found that first-principles generated data yield good agreements with experimental values and thus can be used as key 'experimental data', which are needed for CALPHAD approach.

scholarly journals Standard Molar Enthalpies of Formation of Halomethanes Based on Quantum Chemical Computations

2020 ◽  
Author(s):  
Konstantinos Kalamatianos
Keyword(s):  
Gas Phase ◽  
Quantum Chemical ◽  
Halogen Bond ◽  
Chemical Processes ◽  
Enthalpies Of Formation ◽  
Isodesmic Reaction ◽  
Gold Standard Method ◽  
Ozone Destruction ◽  
Quantum Chemical Computations ◽  
Reaction Schemes

Accurate calculations of standard molar enthalpies of formation (ΔΗf°)m(g) and carbon-halogen bond dissociation enthalpies, BDE, of a variety of halomethanes with relevance on several atmospheric chemical processes and particularly to ozone destruction, were performed in the gas phase at 298.15 K. The (ΔΗf°)m(g) of the radicals formed through bond dissociations have also been computed. Ab initio computational methods and isodesmic reaction schemes were used. It is found that for the large majority of these species, the gold standard method of quantum chemistry (CCSD(T)) and even MP2 are capable to predict enthalpy values nearing chemical accuracy provided that isodesmic reaction schemes are used. New estimates for standard molar enthalpies of formation and BDE are suggested including for species that to our knowledge there are no experimental (ΔΗf°)m(g) (CHCl2Br, CHBr2Cl, CHBrCl, CHICl, CHIBr) or BDE values (CHCl2Br, CHBr2Cl, CHBrCl, CHICl, CHIBr) available in the literature. The method and calculational procedures presented may profitably be used to obtain accurate (ΔΗf°)m(g) and BDE values for these species.

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