Studies on the iodide–triiodide equilibrium

1977 ◽  
Vol 55 (5) ◽  
pp. 792-797 ◽  
Author(s):  
Robert L. Benoit ◽  
Michael F. Wilson ◽  
Sing-Yeung Lam
Keyword(s):  
Free Energy ◽  
Solvent Effect ◽  
Gas Phase ◽  
Formation Enthalpy ◽  
Aprotic Solvents ◽  
Free Energies ◽  
Potentiometric Measurements ◽  
Cast Doubt ◽  
Transfer Parameters ◽  
The Enthalpy Of Formation

The solvent effect on the iodide–triiodide equilibrium has been investigated by means of calorimetric and potentiometric measurements. The aprotic solvents studied were nitromethane, nitrobenzene, sulfolane, acetonitrile, propylene carbonate, acetophenone, dimethylformamide, dimethylsulfoxide, and o-dichlorobenzene. The resulting enthalpy and free energy changes imply that the variations of the enthalpies and free energies of transfer of the iodide and triiodide ions probably are small and that there is an important non-coulombic contribution to these transfer parameters. Values were obtained for the enthalpy of formation of two solid triiodides, which together with values for other triiodides, cast doubt on reported calculated lattice enthalpies of triiodides and formation enthalpy of I3− ion in the gas phase. This latter formation enthalpy is found to be, from our solution data, more negative than −22 kcal mol−1.

Thermodynamic studies in solution. Part IV. Solvent effect on the solvolysis of tert-butyl chloride. A new treatment of the experimental data

1979 ◽  
Vol 57 (5) ◽  
pp. 500-502 ◽  
Author(s):  
Joaquim Jose Moura Ramos ◽  
Jacques Reisse ◽  
M. H. Abraham
Keyword(s):  
Free Energy ◽  
Solvent Effect ◽  
Free Energies ◽  
Butyl Chloride ◽  
Activation Free Energy ◽  
Tert Butyl ◽  
New Treatment ◽  
The One ◽  
Activated Complex ◽  
Tert Butyl Chloride

A new treatment of the solvent effect on the solvolysis of tert-butyl chloride is proposed. This treatment is based on activation free energy measurements and on transfer free energy measurements of the reactant (R) on the one hand and of a model (M) of the activated complex (AC) on the other hand. Solute–solvent interaction free energies for the reactant, the activated complex and the model compound are estimated. This estimation involves the calculation of the free energy of cavity formation of these various solutes (R, AC, and M) in all the solvents. These cavity terms, which are a function of the cohesive properties of the solvent and of the surface of the cavity do not reflect the electronic structure of the solute whereas the interaction free energy term does. The method we propose can be described as a new 'experimental' approach for the study of the charge separation in an activated complex.

Formation Enthalpy, Free-Energy and Activity Coefficients of Sn-Pb Eutectic Solders

2009 ◽  
Vol 610-613 ◽  
pp. 531-536 ◽  
Author(s):  
Gui Sheng Gan ◽  
Fang Chen ◽  
Rong Chang Zeng ◽  
Yun Fei Du ◽  
Chang Hua Du
Keyword(s):  
Free Energy ◽  
High Temperature ◽  
Enthalpy Of Formation ◽  
Activity Coefficients ◽  
Excess Free Energy ◽  
Formation Enthalpy ◽  
Chemical Activity ◽  
Lead Pollution ◽  
The Relationship ◽  
The Enthalpy Of Formation

Based on Miedema’s model, the enthalpy of formation, excess free-energy and partial molar excess free-energy of Sn-Pb binary alloy solders were calculated. The model of the activity coefficient for each component in the solders was established. The diagrams of enthalpy of formation, free energy versus composition and activity versus composition and temperature as well as activity coefficients as a function of composition and/or temperature were drawn. And then the relationship between the activity coefficients of elements Sn/Pb in the solders and temperature was obtained. The approaches to reduction in the volatilization of lead at high temperature were proposed from the point of views that the lead pollution to environment results from its chemical activity in the solder alloys.

Are thermodynamic cycles necessary for continuum solvent calculation of pKas and reduction potentials?

2015 ◽  
Vol 17 (4) ◽  
pp. 2859-2868 ◽  
Author(s):  
Junming Ho
Keyword(s):  
Free Energy ◽  
Gas Phase ◽  
Thermodynamic Cycle ◽  
Free Energies ◽  
Thermodynamic Cycles ◽  
Reduction Potentials ◽  
Reaction Free Energy

Continuum solvent calculations of pKas and reduction potentials usually entail the use of a thermodynamic cycle to express the reaction free energy in terms of gas phase energies and free energies of solvation.

Thermochemistry in the system Cu–In–S at 723 K

1994 ◽  
Vol 9 (1) ◽  
pp. 125-131 ◽  
Author(s):  
H. Migge ◽  
J. Grzanna
Keyword(s):  
Thin Film ◽  
Free Energy ◽  
Solar Cells ◽  
Formation Enthalpy ◽  
Thin Film Solar Cells ◽  
Free Energies ◽  
Base Materials ◽  
Gibbs Triangle ◽  
Standard Formation Enthalpy ◽  
New Literature

A thermochemical analysis is performed in the system Cu-In-S at 723 K. Free energies of In6,S7, In417S583, “In2S3”, Cu951In49, and CuIn5S8 have been estimated, the numerical values (kJ/mol) of which are −1285, −97 780, −481.1, −31 680, and −1444. The free energy (kJ/mol) of CuInS2 is calculated from the relation G° = (-306.1 ± 54.4) + 0.5092T −1.397 10−5T2 −0.09468T In T + 268.2T−1, which is obtained from published assessed standard formation enthalpy and specific heat and entropy data. The free energy of the Cu-In melt is taken from very new literature. A consistent set of data is used for the calculation of a tentative Gibbs triangle as well as of the corresponding predominance area diagram. The Gibbs triangle is calculated with the program thermo, the algorithm of which is given. The results are in agreement with the results of published measurements, also for the equilibria which involve the melt. The compound CuInS2, one of the possible base materials for thin film solar cells, is shown to equilibrate with most of the compounds of the system. Predictions are made how to prepare CuInS2 from Cu-In alloys and H2S/H2 gas mixtures. However, more experiments are necessary to establish the data, the experiments, and/or the results of the calculations.

scholarly journals The Good, the Bad, and the Ugly: “HiPen”, a New Dataset for Validating (S)QM/MM Free Energy Simulations

Molecules ◽  
2019 ◽  
Vol 24 (4) ◽  
pp. 681 ◽  
Author(s):  
Fiona Kearns ◽  
Luke Warrensford ◽  
Stefan Boresch ◽  
H. Woodcock
Keyword(s):  
Free Energy ◽  
Gas Phase ◽  
Convergence Criteria ◽  
Free Energies ◽  
Acceptance Ratio ◽  
Current State ◽  
Energy Perturbation ◽  
Energy Simulations ◽  
Molecular Description ◽  
Bennett’S Acceptance Ratio

Indirect (S)QM/MM free energy simulations (FES) are vital to efficiently incorporating sufficient sampling and accurate (QM) energetic evaluations when estimating free energies of practical/experimental interest. Connecting between levels of theory, i.e., calculating Δ A l o w → h i g h , remains to be the most challenging step within an indirect FES protocol. To improve calculations of Δ A l o w → h i g h , we must: (1) compare the performance of all FES methods currently available; and (2) compile and maintain datasets of Δ A l o w → h i g h calculated for a wide-variety of molecules so that future practitioners may replicate or improve upon the current state-of-the-art. Towards these two aims, we introduce a new dataset, “HiPen”, which tabulates Δ A g a s M M → 3 o b (the free energy associated with switching from an M M to an S C C − D F T B molecular description using the 3ob parameter set in gas phase), calculated for 22 drug-like small molecules. We compare the calculation of this value using free energy perturbation, Bennett’s acceptance ratio, Jarzynski’s equation, and Crooks’ equation. We also predict the reliability of each calculated Δ A g a s M M → 3 o b by evaluating several convergence criteria including sample size hysteresis, overlap statistics, and bias metric ( Π ). Within the total dataset, three distinct categories of molecules emerge: the “good” molecules, for which we can obtain converged Δ A g a s M M → 3 o b using Jarzynski’s equation; “bad” molecules which require Crooks’ equation to obtain a converged Δ A g a s M M → 3 o b ; and “ugly” molecules for which we cannot obtain reliably converged Δ A g a s M M → 3 o b with either Jarzynski’s or Crooks’ equations. We discuss, in depth, results from several example molecules in each of these categories and describe how dihedral discrepancies between levels of theory cause convergence failures even for these gas phase free energy simulations.

Glutathione radical: Intramolecular H abstraction by the thiyl radical

2001 ◽  
Vol 79 (4) ◽  
pp. 405-417 ◽  
Author(s):  
A Rauk ◽  
D A Armstrong ◽  
J Berges
Keyword(s):  
Free Energy ◽  
Gas Phase ◽  
Hydrogen Transfer ◽  
Single Point ◽  
Continuum Models ◽  
Thiyl Radical ◽  
Free Energies ◽  
Model Compounds ◽  
Activation Free Energy ◽  
Transition Structures

Ab initio computations (B3LYP/6-31G(D)) were used to predict transition structures and energies of activation for intramolecular H atom transfer to a thiyl radical (RS.) from the α-C—H bonds of glutathione (1) and from the model compounds, N-formylcysteinylglycine (2) and N-(2-thioethanyl)-γ-glutamine (3). For each compound, transition structures were located by in vacuo calculations on the neutral non-zwitterionic system. Thermodynamic functions derived at the same level and single point calculations at the B3LYP/6-311+G(3df,2p) level, were used to derive free energies of activation (ΔG[Formula: see text]) and reaction (ΔG°). For abstraction of the α-C—H (Gly) by the thiyl radical in the gas phase, ΔG[Formula: see text] = 134 kJ mol–1 if the amide link to Gly is in the more stable (Z)-configuration, and ΔG[Formula: see text] = 52 kJ mol–1 if it is in the less stable (E)-configuration. The isomerization of the amide group requires about 95 kJ mol–1. Previous studies had indicated that for intramolecular reaction of the thiyl radical at α-C—H (Cys), ΔG[Formula: see text] = 110 kJ mol–1. The lowest energy pathway for intramolecular H-transfer to the thiyl radical is from α-C—H (Gln), ΔG[Formula: see text] = 37–42 kJ mol–1, and corresponds rather well with experimental results in solution (ΔG[Formula: see text] = 43 kJ mol–1). The calculated free energy change for the equilibrium between thiyl and α-C forms of the glutathione radical is ΔG° = –54 kJ mol–1. The value estimated from experimental data is ΔG° = –37 kJ mol–1. The agreement between the energies from theory in the gas phase and experiment in solution suggests that the free energies of solvation of reactant thiyl radical, transition structures for H abstraction, and the product α-C-centred radical, are very similar. The effects of solution were estimated by two continuum models (SCIPCM and COSMO). The SCIPCM model yields results very similar to the gas phase, predicting a modest lowering of the activation free energy. The results from the COSMO method were inconclusive as to whether a rate enhancement or decrease could be expected.Key words: glutathione, thiyl radical, α-C-radical, hydrogen transfer.

Gas-phase energy of the S2←S0 transition and electrostatic properties of the S2 state of carotenoid peridinin via a solvatochromic shift and orientation broadening of the absorption spectrum

2014 ◽  
Vol 13 (10) ◽  
pp. 1444-1455 ◽  
Author(s):  
Vladimir S. Pavlovich
Keyword(s):  
Absorption Spectrum ◽  
Solvent Effect ◽  
Temperature Effect ◽  
Gas Phase ◽  
Aprotic Solvents ◽  
Cavity Model ◽  
Solvatochromic Shift ◽  
Electrostatic Properties ◽  
S2 State

The solvent effect on the position and the shape of the absorption spectrum of peridinin for 12 protic and aprotic solvents as well as the temperature effect for methanol were studied using a solvatochromic theory based on the Onsager sphere cavity model.

Prediction of Alkanolamine pKa Values by Combined Molecular Dynamics Free Energy Simulations and ab initio Calculations

2019 ◽  
Author(s):  
Javad Noroozi ◽  
William Smith
Keyword(s):  
Molecular Dynamics ◽  
Free Energy ◽  
Ab Initio Calculations ◽  
Gas Phase ◽  
Quantum Chemical ◽  
Phase Reaction ◽  
Pka Values ◽  
Gas Phase Reaction ◽  
Reaction Free Energy ◽  
Energy Simulations

We use molecular dynamics free energy simulations in conjunction with quantum chemical calculations of gas phase reaction free energy to predict alkanolamines pka values. <br>

On the trustability of semi-empirical methods to the calculation of gas phase formation enthalpies of inorganic compounds containing heavy metals: tin borates

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Heavy Metals ◽  
Gas Phase ◽  
Phase Formation ◽  
Inorganic Compounds ◽  
Formation Enthalpy ◽  
Computational Time ◽  
Gas Formation ◽  
Formation Enthalpies ◽  
Knudsen Effusion Mass Spectrometry ◽  
Semi Empirical

<p>In the present work, are calculated the gas formation enthalpies (SE; PM3 and PM6) for tin borates: SnB<sub>2</sub>O<sub>4</sub><sup> </sup>and Sn<sub>2</sub>B<sub>2</sub>O<sub>5</sub>. The calculated values are compared with experimental ones, obtained by Knudsen effusion mass spectrometry [3]. It is shown that SE methods, besides their lower computational time consuming can, indeed, provide reliable gas phase formation enthalpy values for inorganic compounds containing heavy metals.</p>

Explaining the magnetism of gold

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Gas Phase ◽  
Computational Study ◽  
Formation Enthalpy ◽  
Gold Atom ◽  
Orbital Energy ◽  
Knudsen Effusion ◽  
Energy Diagram ◽  
Unpaired Electrons ◽  
The Difference ◽  
Good Agreement

<p>In the present work, a computational study is performed in order to clarify the possible magnetic nature of gold. For such purpose, gas phase Au<sub>2</sub> (zero charge) is modelled, in order to calculate its gas phase formation enthalpy. The calculated values were compared with the experimental value obtained by means of Knudsen effusion mass spectrometric studies [5]. Based on the obtained formation enthalpy values for Au<sub>2</sub>, the compound with two unpaired electrons is the most probable one. The calculated ionization energy of modelled Au<sub>2</sub> with two unpaired electrons is 8.94 eV and with zero unpaired electrons, 11.42 eV. The difference (11.42-8.94 = 2.48 eV = 239.29 kJmol<sup>-1</sup>), is in very good agreement with the experimental value of 226.2 ± 0.5 kJmol<sup>-1</sup> to the Au-Au bond<sup>7</sup>. So, as expected, in the specie with none unpaired electrons, the two 6s<sup>1</sup> (one of each gold atom) are paired, forming a chemical bond with bond order 1. On the other hand, in Au<sub>2</sub> with two unpaired electrons, the s-d hybridization prevails, because the relativistic contributions. A molecular orbital energy diagram for gas phase Au<sub>2</sub> is proposed, explaining its paramagnetism (and, by extension, the paramagnetism of gold clusters and nanoparticles).</p>

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