Caging and solvent effects on the tautomeric equilibrium of 3-pyridone/3-hydroxypyridine in the ground state: a study in cyclodextrins and binary solvents

2009 ◽  
Vol 11 (26) ◽  
pp. 5377 ◽  
Author(s):  
Osama K. Abou-Zied ◽  
Othman I. K. Al-Shihi
Keyword(s):  
Solvent Effects ◽  
Ground State ◽  
Tautomeric Equilibrium ◽  
Binary Solvents

QM/MM Car-Parrinello Molecular Dynamics Study of the Solvent Effects on the Ground State and on the First Excited Singlet State of Acetone in Water

ChemPhysChem ◽  
2003 ◽  
Vol 4 (11) ◽  
pp. 1177-1182 ◽  
Author(s):  
Ute F. Röhrig ◽  
Irmgard Frank ◽  
Jürg Hutter ◽  
Alessandro Laio ◽  
Joost VandeVondele ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Solvent Effects ◽  
Ground State ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet

Solvent effects on the tautomeric equilibrium of 2,4-pentanedione

1982 ◽  
Vol 60 (10) ◽  
pp. 1178-1182 ◽  
Author(s):  
J. N. Spencer ◽  
Eric S. Holmboe ◽  
Mindy R. Kirshenbaum ◽  
Daniel W. Firth ◽  
Patricia B. Pinto
Keyword(s):  
Hydrogen Bond ◽  
Solvent Effects ◽  
Tautomeric Equilibrium ◽  
Spectroscopic Techniques ◽  
Hydrogen Bond Formation ◽  
Entropy Changes ◽  
Tautomeric Forms ◽  
Self Association ◽  
Enol Tautomer ◽  
Intramolecular Hydrogen

The influence of solvent on the equilibrium position of the tautomeric forms of 2,4-pentanedione was studied by calorimetric and nmr spectroscopic techniques. For solvents such as CCl4 and cyclohexane the intramolecular bond of the enol form persists and bulk solvent effects account for the equilibrium enol–keto content. In solvents such as DMSO, disruption of the intramolecular bond occurs and the percentage of enol falls due to unfavorable entropy changes. The enol intramolecular bond is disrupted by the solvents water and methanol. Enol hydrogen bond formation through self-association and with the solvent accounts for the entropy changes upon enolization in these solvents. The thermodynamic parameters for enolization in neat 2,4-pentanedione are rationalized by the disruption of the enol intramolecular hydrogen bond through consequent polymerization of the enol tautomer.

scholarly journals Role of water in determining organic reactivity in aqueous binary solvents

2012 ◽  
Vol 10 (5) ◽  
pp. 1600-1608 ◽  
Author(s):  
Siim Salmar ◽  
Jaak Järv ◽  
Tiina Tenno ◽  
Ants Tuulmets
Keyword(s):  
Organic Solvent ◽  
Solvent Effects ◽  
Kinetic Data ◽  
Pure Water ◽  
Binary Solvents ◽  
Log P ◽  
Solvent Mixtures ◽  
Similarity Coefficients ◽  
Linear Free Energy ◽  
Organic Cosolvent

AbstractKinetic data for organic reactions in various binary water-organic solvent mixtures were collected and quantitatively analysed in terms of linear-free-energy relationships by using tert-butyl chloride (2-chloro-2-methylpropane) solvolysis as the reference system. Linear similarity plots for these kinetic data were determined for solvent systems ranging from pure water mixtures up to considerable amount of cosolvent, and 161 similarity coefficients were calculated from slopes of these plots. The existence of these linear plots demonstrated that the solvent effects are of some common nature in all analysed reaction mixtures independent of the reaction type and the cosolvent used. Therefore it was concluded that the observed effects could be connected to the specific solvating properties of water, which govern reactivity even in significant dilution of water by an organic cosolvent. This conclusion was supported by the linear interrelationship between the slopes of similarity plots of different reactions, and hydrophobicity parameters log P of the reacting compounds. The relative solvent effects observed in binary water-organic solvent mixtures were for the first time directly related to the structure of reacting compounds.

Fluorescence Emission Properties of the Cation of 4-Aminopyrazole(3,4-d) pyrimidine, an Adenine Analogue: Evidence for Phototautomerism

1980 ◽  
Vol 35 (11-12) ◽  
pp. 878-889 ◽  
Author(s):  
Jacek Wierzchowski ◽  
Marian Szczęśniak ◽  
David Shugar
Keyword(s):  
Ground State ◽  
Emission Band ◽  
Aqueous Media ◽  
Fluorescence Emission ◽  
Emission Spectra ◽  
Wavelength Dependence ◽  
Tautomeric Equilibrium ◽  
Excitation Spectra ◽  
Tautomeric Forms ◽  
Wavelength Emission

A study has been made of the emission spectra at room temperature, in aqueous and alcoholic media, of 4-aminopyrazolo(3,4-d)pyrimidine (APP) and some of its methylated derivatives. The cationic forms APPH+, N2-methyl-APPH+ and N7-methyl-APPH+ exhibit intense fluorescence un­der these conditions, the first two exhibiting excitation spectra which differ from the absorption spectra, pointing to the existence of a tautomeric equilibrium in the ground state. From the shape of the excitation spectra, and comparisons with methylated analogues in fixed tautomeric forms, it follows that the emission of APPH+ originates exclusively from the species N(2)-H,N(7)-H+, the other forms being non-fluorescent. The proportion of the emitting species, calculated from the ex­citation wavelength dependence of the quantum yield, is in good agreement with data for the ground state. The emission spectrum of APPH+ in aqueous medium consists of two bands with λmax 360 nm and 430 nm, which exhibit identical excitation spectra, but are quenched to different extents by H3O+. The 430 nm emission band is absent in alcoholic media. A similar behaviour is exhibited by N7-methyl-APPH+, whereas the neutral form of this analogue exhibits only the 430 nm band. These results indicate that the long wavelength emission band of APPH+ originates from the rare tautomeric species N(7)-H formed in the excited state by photodissociation of the N(2)-H proton from the species N(2)-H,N(7)-H+. This is further confirmed by results obtained with the aid of the basicity method, as well as by salt efects in non-aqueous media. Consideration is given to the possibility of such processes occurring in other analogues of nucleic acid derivatives.

Keto - Enol Tautomerism as a Polarity Indicator in Ionic Liquids

2004 ◽  
Vol 57 (2) ◽  
pp. 149 ◽  
Author(s):  
Martyn J. Earle ◽  
Brian S. Engel ◽  
Kenneth R. Seddon
Keyword(s):  
Ionic Liquids ◽  
Ground State ◽  
Tautomeric Equilibrium

The keto–enol tautomeric equilibrium for pentane-2,4-dione has been explored in several ionic liquids and these data have been used to give an indication of their polarities in the ground state. The results suggest higher apparent polarities than have been previously indicated by the use of solvatochromatic dyes.

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