Tautomerization equilibria for phosphorous acid and its ethyl esters, free energies of formation of phosphorous and phosphonic acids and their ethyl esters, and pKa values for ionization of the P—H bond in phosphonic acid and phosphonic esters

1979 ◽  
Vol 57 (2) ◽  
pp. 236-239 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Equilibrium Constants ◽  
Phosphorous Acid ◽  
Triethyl Phosphite ◽  
Ethyl Esters ◽  
Free Energies ◽  
Phosphonic Acids ◽  
Hydroxy Compounds ◽  
Energy Relations

From data in the literature the free energies of formation in aqueous solution of triethyl phosphite and diethyl phosphonate can be calculated as −138.4 ± 1.7 and −165.1 ± 2.0 kcal mol−1, respectively. From these values, by application of free energy relations which we have published, the free energies of formation of the corresponding hydroxy compounds can be calculated and thence the equilibrium constants for tautomerization, which are 107.2, 108.7, and 1010.3 in favor of the tetracoordinate phosphonate tautomer for P(OEt)2OH, P(OEt)(OH)2, and P(OH)3, respectively. Using estimated pKa values for the tricoordinate phosphite species the tautomerization equilibria for the anions could also be calculated, as could the pKa values from the P—H bonds: 13, 26, and 38 for H—PO(OEt)2, H—PO2(OEt)−, and H—PO32−, respectively.

Equilibrium constants for a series of simple aldol condensations, and linear free energy relations with other carbonyl addition reactions

1978 ◽  
Vol 56 (7) ◽  
pp. 962-973 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Free Energy ◽  
Acetic Acid ◽  
Carbonyl Compounds ◽  
Equilibrium Constants ◽  
Linear Free Energy Relationship ◽  
Reaction Products ◽  
Free Energies ◽  
Linear Free Energy ◽  
Energy Relations ◽  
Relationship Of

A set of equilibrium constants for aldol condensations of acetaldehyde, acetone, acetophenone, and acetic acid as nucleophiles and formaldehyde, acetaldehyde, benzaldehyde, acetone, and acetophenone as carbonyl acceptors has been evaluated. The four values determined, directly or indirectly, by experiment have been augmented by values calculated from thermo-chemical data and equilibrium constants for enone hydration, and by estimation of free energies of formation of the reaction products by use of hypothetical disproportionation reactions. When the carbonyl nucleophiles are compared to other nucleophiles which can add to carbonyl compounds, it is found that they can be incorporated in the linear free energy relationship of Sander and Jencks, with γ values of 0.45 for acetaldehyde, 0.16 for acetone, 0.05 for acetophenone, and 3.56 for acetic acid. These results make it possible to predict the equilibrium constants for any of a large number of aldol condensations from the equilibrium constant for the addition of any nucleophile to the carbonyl accepter compound.

Article

1999 ◽  
Vol 77 (5-6) ◽  
pp. 934-942
Author(s):  
J Peter Guthrie
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Equilibrium Constants ◽  
Marcus Theory ◽  
Energy Of Activation ◽  
Free Energies ◽  
Orbital Theory ◽  
Activation Free Energy ◽  
Free Energy Of Activation ◽  
Rms Error

Rate constants for hydration of carbon dioxide and ketene can be calculated by applying No Barrier Theory, which needs only equilibrium constants and distortion energies, the latter calculated using molecular orbital theory. The calculated free energies of activation are in satisfactory agreement with experiment: the rms error in free energy of activation is 2.38 kcal/mol. These compounds can also be described using Marcus Theory or Multidimensional Marcus Theory using the transferable intrinsic barrier appropriate to simple carbonyl compounds; in this case the rms error in free energy of activation is 2.19 kcal/mol. The two methods agree on preferred mechanistic path except for uncatalyzed hydration of ketene where Multidimensional Marcus Theory leads to a lower activation free energy for addition to the C=O, while No Barrier Theory leads to a lower free energy of activation for addition to the C=CH2. A rate constant for hydroxide ion catalyzed hydration of ketene can be calculated and is in accord with preliminary experimental results.Key words: ketene, carbon dioxide, hydration, Marcus Theory, No Barrier Theory.

scholarly journals Carbonyl Addition Reactions: Factors Affecting the Hydrate–Hemiacetal and Hemiacetal–Acetal Equilibrium Constants

1975 ◽  
Vol 53 (6) ◽  
pp. 898-906 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Carbonyl Compounds ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Addition Reactions ◽  
Free Energies ◽  
Electronic Effects ◽  
Factors Affecting ◽  
Analogous Formula

Equilibrium constants for hydrate–hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K4 (M−1): CF3CHO, C2H5OH, 2.3; CF3COCH3, CH3OH, 1.0; CF3COPh, CH3OH, 3.5; CF3COCF3, CH3OH, 0.14. These values, combined with values from the literature, permit an examination of substituent effects upon the equilibrium constant for[Formula: see text]The free energy change for this process, corrected for symmetry and steric effects, follows the equation[Formula: see text]Thus electronic effects upon this equilibrium are generally small and in fact are often smaller than steric effects.This analysis permits and justifies the calculation of free energies of formation of [Formula: see text] compounds from the (more generally measurable) free energies of formation of the analogous [Formula: see text] compounds.

Acid Ionizations of Nitroalkanes in Aqueous Solution

1973 ◽  
Vol 51 (12) ◽  
pp. 1941-1944 ◽  
Author(s):  
Takeki Matsui ◽  
Loren G. Hepler
Keyword(s):  
Aqueous Solution ◽  
Carboxylic Acids ◽  
Equilibrium Constants ◽  
Free Energies ◽  
Methyl Substitution ◽  
Calorimetric Measurements ◽  
Acid Ionizations

Calorimetric measurements have led to ΔH0 values for ionization of nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane in aqueous solution at 298°K. Combinations of these enthalpies with free energies from equilibrium constants for ionization have led to ΔS0 values for the ionization reactions. It is noted that the trend toward decreasing pK with methyl substitution in nitroalkanes is unusual compared to phenols and carboxylic acids. Similarly, correlations of ΔS0 with ΔG0 and ΔH0 are different for nitroalkanes than for other acids.

Tautomeric equilibria and pKa values for 'sulfurous acid' in aqueous solution: a thermodynamic analysis

1979 ◽  
Vol 57 (4) ◽  
pp. 454-457 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Aqueous Solutions ◽  
Equilibrium Constants ◽  
Acid Solutions ◽  
Sulfurous Acid ◽  
Free Energy Of Formation ◽  
Dilute Aqueous Solutions ◽  
Sulfite Ion ◽  
Energy Of Formation

The free energy of formation of dimethyl sulfite in aqueous solution can be calculated as −91.45 ± 0.79 kcal/mol; this calculation required measurement of the solubility of dimethyl sulfite. From this value and the pKa of SO(OH)2, using previously reported methods, the free energy of formation of SO(OH)2 can be calculated to be −129.26 ± 0.89 kcal/mol. Comparison of this value with the value obtained from the free energy of formation of 'sulfurous acid' solutions, calculated from the free energy of formation of sulfite ion and the apparent pKa, values, permits evaluation of the free energy of covalent hydration of SO2 as 1.6 + 1.0 kcal/mol, in agreement with earlier qualitative spectroscopic observations. From the apparent pKa and the anticipated pKa values for the tautomers (SO(OH)2, pK1 = 2.3; HSO2(OH), pK1 = −2.6) it is possible to calculate the free energy change for tautomerization of SO(OH)2 to H—SO2(OH) as +4.5 ± 1.2 kcal/mol. All equilibrium constants required for Scheme 1, describing the species present in dilute aqueous solutions of SO2, have been calculated. In agreement with previous Raman studies the major tautomer of 'bisulfite ion' is calculated to be H—SO3−.

scholarly journals Thermodynamics of ester and orthoester formation from trifluoroacetic acid

1976 ◽  
Vol 54 (2) ◽  
pp. 202-209 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Equilibrium Constant ◽  
Trifluoroacetic Acid ◽  
Sodium Methoxide ◽  
Standard Free Energy ◽  
Steric Effects ◽  
Addition Reactions ◽  
Free Energies ◽  
Acetic Acids

The equilibrium constant for the addition of sodium methoxide to methyl trifluoroacetate, in methanol as solvent, has been measured by 19F nmr, and is 7 M−1. From this was calculated an equilibrium constant, 2 × 10−4 M−1, for addition of methanol to the ester. The equilibrium constant for formation of methyl trifluoroacetate in aqueous solutions is 0.06 M−1. These results, with literature data, permit calculation of the free energies of formation in aqueous solution of orthotrifluoroacetic acid and its mono-, di-, and trimethyl esters. These in turn permit calculation of the standard free energy changes for addition of water and methanol to trifluoroacetic acid and its methyl ester. These combined with the analogous values for formic and acetic acids permit evaluation of ρ* values for these addition reactions. Linear plots are obtained if correction is made for steric effects, and the ρ* values are somewhat larger, 2.1–2.9, than was observed for the analogous carbonyl addition reactions.

scholarly journals Regular Associated Solution Model for the Estimation of Free Energy of Mixing of Binary Liquid Alloys

1970 ◽  
Vol 8 (8) ◽  
pp. 30-33
Author(s):  
D Adhikari ◽  
BP Singh ◽  
IS Jha
Keyword(s):  
Free Energy ◽  
Equilibrium Constants ◽  
Solution Model ◽  
Interaction Energies ◽  
Free Energies ◽  
Scientific World ◽  
Energy Of Mixing ◽  
Free Energy Of Mixing ◽  
Associated Solution Model ◽  
Associated Solution

We have found the equilibrium constants and pairwise interaction energies between the species and the complexes of liquid CuSn, AgAl, FeSi, CdNa and HgNa alloys on the basis of regular associated solution model. These parameters are then used to estimate the free energies of mixing of each alloy. The observed asymmetry in the free energy of mixing of each alloy with respect to concentration is well explained. Key Words: Free energy of mixing; Asymmetry; Binary alloys; Interaction energy. DOI: 10.3126/sw.v8i8.3842 Scientific World Vol.8(8) 2010 pp.30-33

scholarly journals Measuring Theoretical Descriptors of Water Oxidation: Free Energy Differences Between Intermediates Using Time-Resolved Optical Spectroscopy

2021 ◽  
Author(s):  
Ilya Vinogradov ◽  
Suryansh Singh ◽  
Hanna Lyle ◽  
Aritra Mandal ◽  
Jan Rossmeisl ◽  
...  
Keyword(s):  
Free Energy ◽  
Water Oxidation ◽  
Oxidation Reaction ◽  
Equilibrium Constants ◽  
Semiconductor Surface ◽  
Free Energies ◽  
Time Resolved ◽  
Time Resolved Spectroscopy ◽  
Material Surfaces ◽  
The Stability

<p>Theoretical descriptions differentiate catalytic activity of material surfaces for the water oxidation reaction by the stability of the reactive oxygen (O*) intermediate. The underlying conjecture is that there are several meta-stable steps of the reaction, each connected by free energy differences critically dependent on O*. Recently <i>in-situ, </i>time-resolved spectroscopy of the (<i>photo<br> </i>)-electrochemical water oxidation reaction identified the vibrational and optical signatures of O* time-evolution. However, there has been little connection between these inherently kinetic experiments and the underlying thermodynamic parameters of the theory. Here, we discover that picosecond optical spectra of the O* population modulated by a shift in reaction equilibria defines an effective equilibrium constant (K<sub>eff</sub>) containing the relevant free-energy differences. A Langmuir isotherm as a function of electrolyte pH extracts K<sub>eff</sub> using a model titania system (SrTiO<sub>3</sub>). The results show how to obtain equilibrium constants of individual reaction steps on material surfaces, which had not been experimentally accessible previously. Further, we find that for a photo-excited reaction on a semiconductor surface tuning past a pH defined by K<sub>eff</sub> doubles the initial O* population. That the free energies of the catalytic surface are definable through a time-resolved spectroscopy, alongside the finding that the surface recollects its explicit equilibrium with the electrolyte, provides a new and critical connection between theory and experiment by which to tailor the pathway of water oxidation and other surface reactions.</p>

Conformational analysis in carbohydrate chemistry. I. Conformational free energies. The conformations and α : β ratios of aldopyranoses in aqueous solution

1968 ◽  
Vol 21 (11) ◽  
pp. 2737 ◽  
Author(s):  
SJ Angyal
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Conformational Analysis ◽  
Reasonable Agreement ◽  
Anomeric Effect ◽  
Interaction Energies ◽  
Free Energies ◽  
Carbohydrate Chemistry ◽  
Predominant Conformation

The relative free energies of the aldopyranoses in aqueous solution have been calculated, taking non-bonded interaction energies and the anomeric effect into account. It is shown that the calculated free-energy values correctly predict the predominant conformation of the α- and β-pyranose forms of each aldose. The α- to β-pyranose ratios of the aldoses in aqueous solution, calculated from these values, are in reasonable agreement with those determined experimentally.

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