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The pi-Electron Delocalization Imposed by Thermal Vibrations of Substituted Benzene Analogues in Mediums of Varying Polarities

Cysewski P., Jeliński T.

Computational Methods in Science and Technology

2011

Vol. 17, No. 1-2

5-15

The unique set of aromaticity indices was identified for thermally induced changes of pi-electron delocalization by means of PCA (Principal Component Analysis). It was demonstrated that solvents polarity can influence not only the values of aromaticity indices but also their contribution to Principal Components. Therefore, in different phases one should select different indices for a proper description of the aromaticity. The found aromaticity diversities indices were provided for aniline as well as p-nitrosoaniline and it was found that the geometry of the latter one is highly sensitive to solvents polarity changes. Thus, all of the aromaticity indices experienced a reduction of their values, with the HOMA (Harmonic Oscillator Model of Aromaticity) index being the most sensitive. It was also found that there were such vibrations which could alter this trend and lead to apparent increase of aromaticity.

Modelling hydrogen-bonded crystal structures beyond resolution of diffraction methods

Katrusiak A.

Polish Journal of Chemistry

1998

Vol. 72, nr 2

449-459

Knowledge of molecular geometry, combined with the prediction of preferred molecular orientation, can yield details of disordered crystal structures difficult to investigate by diffraction methods. The R-OH- -O'-R' hydrogen bond dimensions O-H, H- -O, R-O-H, and H- -O'-R' chiefly depend on the electronic structure of the proton-donor and acceptor groups. Thus, when hydrogen-bonded aggregates undergo transformations, such as hydrogen-bonds breaking, concerted H-transfers or H-disordering, the molecular rearrangements are coupled with the H-sites. This interdependence is exemplified by a one-dimensional model of a hydrogen-bonded aggregate, and the real structures and thermodynamic properties of H2O ice and H3BO3 orthoboric acid.