Zbigniew Kecki

Vibrational frequencies and force constants of N2O4 in complexes with molecules of different solvents determined by Raman spectra andAb initio calculation

The Raman spectra of N2O4 solutions in organic solvents have been recorded. The frequencies ofv1,v2, andv3 bands of N2O4 increase with increasing solvent electron-donor properties. Especially large changes ofv3 N-N stretching band have been observed (254.5 cm−1 in n-hexane, 276.5 cm−1 in 1,4-dioxane). The ab initio calculations have shown that the interaction between N2O4 and electron-donor molecules causes an increase of N-N and N-O stretching and O-N-O bending force constants of N2O4 in agreement with the results of Raman study.

Critical comparison of empirical systems used to describe solvent properties

The hyperfine splitting constant AN of nitroxide radical signals in EPR was measured and correlated with several systems of solvent parameters in 26 solvents. The linear correlation data show the dielectric approach is in general not appropriate to determine the properties of solvents. A proper description of solvent effects can be achieved only by the parameters sensitive to the electron charge density redistributions.

EPR study of the dinitrogen tetroxide dissociation in organic solvents

The dinitrogen tetroxide homolytical dissociation constants KDIS are determined in organic solvents. The values are the highest in non-donor and the lowest in n-donor solvents. The variations of KDIS with solvent are interpreted in terms of electron donor-acceptor interactions between dinitrogen tetroxide and electron donor molecules.

Hydrogen bonding in fluoranilines studied by means of a nitroxide radical probe

Abstract 1 H, 13 C and 15 N NMR chemical shifts were measured for aniline and its five fluoro derivatives dissolved in CCl 4 . The EPR spectrum of the 2,2,6,6-tetramethylpiperidine nitroxide (TMPN) radical was used as a probe to study the changes in hydrogen bonding between the aniline NH 2 group after fluorine substitution and the ON group of the radical. The coupling constant A( 14 N) increases with the number of fluorine atoms substituted in aniline. NMR contact shifts indicate a positive spin density of C4 and C2,6 aniline atoms and a negative spin density on the Cl atom and on the hydrogen atoms of the NH 2 group.

N2O4 complexes with electron donor molecules. An STO-3G study

The quantum chemical calculations for N2O4 complexes with some electron-donor molecules: CH3NO2, CH3COOH, CH3CN, C6H6 and with another molecule of N2O4 show that the donor molecule lies under the N2O4 plane and its electron-donor atom points to the center of N-N bond of N2O4 (or near this center). The electron charge is transferred from the donor to N2O4 molecule, mostly to the N-N bond of N2O4.