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.

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.

Free energies of solvation with quantum mechanical interaction energies from classical mechanical simulations

1999 ◽  
Vol 110 (3) ◽  
pp. 1329-1337 ◽  
Author(s):  
Robert H. Wood ◽  
Eric M. Yezdimer ◽  
Shinichi Sakane ◽  
Jose A. Barriocanal ◽  
Douglas J. Doren
Keyword(s):  
Quantum Mechanical ◽  
Interaction Energies ◽  
Free Energies ◽  
Mechanical Interaction

Concerning the relevance of ethane conformational analysis to acyclic aldol transition states

1982 ◽  
Vol 23 (47) ◽  
pp. 4891-4894 ◽  
Author(s):  
Dennis A. Dougherty
Keyword(s):  
Conformational Analysis ◽  
Transition States

Acyclic and cyclic nitrone cycloadditions to 1-cinnamoyl-1-piperidine: A DFT study

2014 ◽  
Vol 13 (08) ◽  
pp. 1450071 ◽  
Author(s):  
Nivedita Acharjee
Keyword(s):  
Transition States ◽  
Activation Parameters ◽  
Interaction Energies ◽  
Reactivity Indices ◽  
Chemical Potentials ◽  
Experimental Findings ◽  
Electronic Chemical ◽  
Wiberg Bond Indices ◽  
Electron Demand ◽  
Trajectory Simulations

DFT studies have been carried out for the cycloaddition reactions of a cyclic nitrone, 1-pyrroline-1-oxide and an acyclic nitrone, C,N-diphenyl nitrone to an unsymmetrically disubstituted dipolarophile, 1-cinnamoyl-1-piperidine. These reactions proved to be opposite to each other with respect to the electron demand character predicted by the electronic chemical potentials, electrophilicities and charge transfer at the transition states. The regio- and stereoselectivities have been predicted from DFT based reactivity indices, interaction energy calculations using a perturbative orbital independent theoretical model and the activation parameters of the located transition states. Two different concepts have been used for the evaluation of interaction energies. The selectivities were found to be in conformity with the experimental findings. The time gaps between the formations of C – C and C – O bonds were evaluated from single trajectory simulations. The asynchronicity of bond formation process was analyzed from the wiberg bond indices, atom–atom overlap weighted NAO bond orders and the calculated asymmetry indices of the transition states.

Glycosidation of sugars. IV. Methanolysis of D-glucose, D-galactose, and D-mannose

1968 ◽  
Vol 46 (19) ◽  
pp. 3085-3090 ◽  
Author(s):  
V. Smirnyagin ◽  
C. T. Bishop
Keyword(s):  
Conformational Analysis ◽  
Ground States ◽  
Reaction Proceeds ◽  
Competing Reactions

Rates of methanolysis reactions of D-glucose, D-galactose, and D-mannose have been determined. The results confirm those found earlier for pentoses that the glycosidation reaction proceeds to equilibrium through four distinguishable competing reactions: (1) hexose → furanosides, (2) anomerization of furanosides, (3) furanosides → pyranosides, and (4) anomerization of pyranosides. The glycoside compositions at equilibrium are interpreted in terms of conformational analysis for furanoid and pyranoid rings. The energy differences between the ground states also contribute to an important degree in determining the relative rates of reaction.

scholarly journals Geometries, interaction energies and complexation free energies of 18-crown-6 with neutral molecules

CrystEngComm ◽  
2016 ◽  
Vol 18 (44) ◽  
pp. 8653-8663 ◽  
Author(s):  
Ming W. Shi ◽  
Li-Juan Yu ◽  
Sajesh P. Thomas ◽  
Amir Karton ◽  
Mark A. Spackman
Keyword(s):  
Interaction Energies ◽  
Free Energies

Gas and solution phase thermochemistry and transition energies of NH2• and NH3•+, and their aquo complexes: an ab initio study

1994 ◽  
Vol 72 (3) ◽  
pp. 471-483 ◽  
Author(s):  
Dake Yu ◽  
Arvi Rauk ◽  
David A. Armstrong
Keyword(s):  
Ab Initio ◽  
Binding Energies ◽  
Solution Phase ◽  
Interaction Energies ◽  
Free Energies ◽  
Transition Energies ◽  
Bonding Interaction ◽  
Ab Initio Structure ◽  
Total Energies ◽  
Free Energy Of Solution

Ab initio calculations were performed on several aquo complexes of NH2•, and NH3•+, and on monomeric parent species. The geometries were optimized at the HF/6-31 + G* level and the vibrational frequencies were calculated. The total energies and the binding energies of complexes were evaluated at the MP2/6-31 + G* + ZPE level of theory. Gas and aqueous solution phase thermodynamic properites of NH2• and NH3•+ and several other species were calculated. The examination of solution phase properties of the radicals was facilitated by study of the structures and transition energies of aquo complexes. H-bonding interaction energies decreased in the order [Formula: see text] but were generally stronger than σ–σ* interactions involving the unpaired electron. From calculations with the CIS method, the weak absorption observed at 520 nm for aqueous NH2• is confirmed as a 2B1 → 2A1 transition, while the stronger NH2• absorption occurring below 250 nm and the absorption of NH3•+, which rises monotonically below 370 nm, are attributed to solvent-to-solute charge transfer bands. The solution free energies and related E0 values for NH2• and NH3•+ are in agreement with those of Stanbury. The ab initio structure studies show that water protons are bound to N, and proton transfer from solvent in reaction [18], NH2• + e− + H2O → NH3 + OH−, is likely to be the dominant redox reaction of NH2• in alkaline solution. The free energy of solution of NH3•+ is shown to be larger than that of [Formula: see text].

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.

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