Wyniki wyszukiwania - BazTech

Ograniczanie wyników

2 Polish Journal of Chemistry

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: solvent effects

Sortuj według:

Ogranicz wyniki do:

Assisted and Protected Effects of Methanol Molecules on Intramolecular Proton Transfer in Formamide Studied with the Density Functional Theory

Du M., Qin M., Fu A., Zhou Z.

Polish Journal of Chemistry

2007

Vol. 81, nr 3

369-380

Methanol assisted and protected proton transfers from the amide nitrogen to carbonyl oxygen atom inmodel peptide compound formamide have been investigated employing the B3LYP/6-311++G(d,p) level of theory. In the vicinity of formamide (F) and formamidic acid (FA), three different regions are considered to form hydrogen bond with methanol. Methanol molecule only in one of them can assist the proton transfer reaction while in other two sites can protect formamide from tautomerization. Totally, 27 geometries, including nine important transition states, were optimized, and their geometric parameters have also been discussed in detail. The thermodynamic and kinetic parameters, such as tautomeric energies, equilibrium constants, barrier heights, and rate constants have been predicted, respectively. In addition, the factors influencing the thermodynamic and kinetic parameters, such as temperature dependences, and solvent effects have also been explored qualitatively. Computational results show that the lowest proton transfer barrier heights are 83.30 (61.61) kJ/mol without (with) ZPVE correction for the assistance of two methanol molecules, which are also lower than that of the water-assisted process. Nonspecific solvent effects have also been taken into account by using the IPCM model of methanol. The tautomerization energies and the barrier heights are increased for these proton transfer systems because of the bulk solvent, which imply that the tautomerization of F becomes less favorable in the polar medium.

An Experimental Test for the Approximation of NMR Solvent Effects by Continuum Models. 19F Gas-to-Solution Shifts of SF6 and CF4

Jackowski K., Wilczek M.

Polish Journal of Chemistry

2006

Vol. 80, nr 7

1169-1175

19F gas-to-solution shifts were measured for two solute molecules (SF6, CF4) and 39 organic solvents. A correlation between the results for SF6 and CF4 is satisfactory and proves that solvent effects of both the solute molecules can be described in the same way. The present 19F shifts of SF6 are also compared with some previous gas-to-solution shifts observed for 129Xe gas and 33S in SF6. It is shown that intermolecular interactions change the shifts of external atoms (19F and 129Xe) in slightly different way than it is observed for the central atom of 33S in a SF6 molecule.