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2 Polish Journal of Chemistry

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Evolution of Quantum Similarity Measures: How They Perform in Modeling Hammett Constants

100%

Sadlej-Sosnowska N.

2009

tom Vol. 83, nr 12

2215-2224

This study was aimed at comparing a few measures of similarity of carboxylic acids’ molecules, based on the electronic descriptors derived from molecular wave functions. Five series of molecules were investigated: benzoic acids, thiophene-2-carboxylic acids, furane-2-carboxylic acids, trans-cinnamic acids, and 3-phenylpropionic acids. It has been previously found that in stead of comparing densities or other electronic properties of the entire molecules, it is sufficient to use the properties within a molecular fragment, active towards a given reaction. In this vein, three measures have been compared: the one pertaining to the properties of bond critical points, the one derived from atomic potentials, and that based on Fermi-hole densities, confined to the COOH group. Never the less, it appeared that other ways of defining a similarity measure may also be practical, namely that based on charges of the COOH group and that based on the properties of another molecular fragment, i.e. the substituent and the ring carbon atom connected to the so-called substituent active region. The calculations were carried out at the B3LYP/cc-pVDZ level.

Intramolecular O–H…O Hydrogen Bonds – the Influence of External Agents on Their Properties

84%

Grabowski S.

2007

tom Vol. 81, nr 5-6

799-811

Intramolecular O–H…O hydrogen bond in malonaldehyde is analyzed. Ab inito MP2/6- 311++G(d,p) calculations were carried out for this isolated moiety as well as for malonaldehyde assisted by external systems: Li+, Na+ ions and HF molecule. The latter moieties act as Lewis acids interacting with the oxygen carbonyl atom or with the oxygen hydroxyl atom. The influence of these external agents on the characteristics of H-bond, the -electron delocalization within six-member pseudo-ring and on the proton transfer process is also analyzed. The Bader theory is also applied to characterize intramolecular O–H…O hydrogen bond.