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Effect of the Dielectric Medium on the Conformational Behaviour of Methyl 3-Nitrobenzoate

Konopacka A., Kalenik J., Pawełka Z.

Polish Journal of Chemistry

2006

Vol. 80, nr 9

1583-1592

Conformational analyses of methyl 3-nitrobenzoate (MNB) was performed, employing DFT, MP2, and semi-empirical quantum-chemical calculations, as well as classical methods based on atomic charge and dipole moment approximations. Properties such as the relative energies of the O-NO2 trans and O-NO2 cis isomers, their populations and dipole moments, all in vacuum, were considered first. Then the conformational trans cis equilibrium was quantitatively established by dipole moment measurements in solvents of dielectric permittivities between 2.016 and 10.34. Different approaches, based on continuum-dielectric and MSAmodels were explored to explain the contribution of the electrostatic interaction to the standard Gibbs energy change delta G° of the trans cis transformation in MNB in solution.

Aromatic Solvent Effect on Polarity and Proton-Transfer Equilibrium in Phenol-Triethylamine Systems

Pawełka Z., Kuc T.

Polish Journal of Chemistry

2001

Vol. 75, nr 6

845-855

Dipole moments of hydrogen-bonded complexes of 4-nitrophenol-triethylamine and 2,4,6-trichlorophenol-triethylamine have been determined in various aromatic solvents. On this basis, the Gibbs energy _GPT of the proton-transfer equilibrium has been estimated. The aromatic solvent effect on the proton transfer has been discussed in terms of two solvation contributions, arising from a local complex-aromatic molecules interaction and a long-range dielectric effect. The microstructure of the solvent near a complex has been taken into account, utilizing a dielectric model of two spherical solvent layers. The crucial effect of the size of the aromatic solvent molecules on _GPT has been simulated by variation of the thickness of the first solvation layer.