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.

Conformational analysis in carbohydrate chemistry. II. Equilibria between reducing sugars and their glycosidic anhydrides

1968 ◽  
Vol 21 (11) ◽  
pp. 2747 ◽  
Author(s):  
SJ Angyal ◽  
K Dawes
Keyword(s):  
Gas Chromatography ◽  
Conformational Analysis ◽  
Reducing Sugars ◽  
Interaction Energies ◽  
Carbohydrate Chemistry ◽  
Conformational Interaction ◽  
Good Agreement

The position of the equilibria between aldohexoses and 3-deoxyaldohexoses and their 1,6-anhydrides, and between heptuloses and their 2,7-anhydrides, has been determined by gas chromatography. The results are in good agreement with data calculated from conformational interaction energies. D-Talose gives equal amounts of the 1,6-anhydropyranose and the 1,6-anhydrofuranose. D-glycero-D-gulo-Heptose gives 66% of the 1,7- and only 9% of the 1,6-anhydride.

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.

Conformational analysis in carbohydrate chemistry. III. The 13C N.M.R. spectra of the hexuloses

1976 ◽  
Vol 29 (6) ◽  
pp. 1249 ◽  
Author(s):  
SJ Angyal ◽  
GS Bethell
Keyword(s):  
Aqueous Solution ◽  
Conformational Analysis ◽  
Carbohydrate Chemistry ◽  
Related Compounds

All the resonances have been assigned in the 13C N.M.R. spectra of the hexuloses and some of their derivatives by the use of specifically deuterated compounds and comparison with related compounds. The composition of the hexuloses at equilibrium in aqueous solution has been determined and is discussed in terms of conformational analysis. The synthesis of D-fructose[l-D], D-fructose[3-D] and D-fructose[4-D] is described.

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

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.

GLYCOSIDATION OF SUGARS: II. METHANOLYSIS OF D-XYLOSE, D-ARABINOSE, D-LYXOSE, AND D-RIBOSE

1963 ◽  
Vol 41 (11) ◽  
pp. 2743-2758 ◽  
Author(s):  
C. T. Bishop ◽  
F. P. Cooper
Keyword(s):  
Conformational Analysis ◽  
Excellent Agreement ◽  
Transition States ◽  
Interaction Energies ◽  
Free Energies ◽  
Ionic Effects ◽  
Competing Reactions

Rates of methanolysis reactions of D-xylose, D-arabinose, D-lyxose, and D-ribose have been determined. It was found that methanolysis of a pentose proceeds to equilibrium through four distinguishable, competing reactions: (1) pentose → furanosides; (2) anomerization of furanosides; (3) furanosides → pyranosides; (4) anomerization of pyranosides. The glycoside compositions at equilibrium are interpreted in terms of stabilities of each of the four glycosides from each sugar as influenced by steric and ionic effects; a system of conformational analysis of furanoside rings is presented. The free energies of reaction in anomerization of pyranosides were in excellent agreement with values calculated from previously reported interaction energies in the pyranoid ring. The relative rates of the reactions were consistent with the view that non-bonded interactions in the methyl glycosides are relieved in the transition states for their interconversions.

The influence of dielectric saturation on the thermodynamic properties of aqueous ions

1957 ◽  
Vol 241 (1224) ◽  
pp. 80-92 ◽  
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Small Radius ◽  
Free Energies ◽  
Born Model ◽  
First Approximation ◽  
Born Equation ◽  
Electrostatic Contribution ◽  
Aqueous Ions ◽  
Dielectric Saturation

An examination is made of the applicability of the simple electrostatic (Born) model for ions in aqueous solutions, with special reference to the expressions for free energy, z 2 e 2 /2 r ϵ , and entropy, ( z 2 e 2 /2 r ϵ ) (∂ ln ϵ /∂T). The model is found to be valid to a useful first approximation, but the deviations are significant, particularly for ions of high charge and small radius. Theories of the dielectric constant of water and of its variation with field strength are applied to the case of monatomic ions in aqueous solution, and give rise to an interpretation of the experimental free energies and entropies that is more satisfactory than the simple model. If S͞ 0 e. s. is the electrostatic contribution to the entropy, S͞ 0 e. s. / z 3/2 is found to be a continuous function of z ½ / r , and the Born equation is closely applicable to entropies for values of z ½ / r less than about 0·4. In the case of free energy the Born equation applies over a wider range, up to z ½ / r values of about 0·8.

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