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3 Polish Journal of Chemistry

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

Sadlej-Sosnowska N.

Polish Journal of Chemistry

2009

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

Grabowski S.

Polish Journal of Chemistry

2007

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.

Comparison of the ab-initio calculated and X-ray molecular geometries of the o-, m-, and p-cyanoaniline

Janczak T.

Polish Journal of Chemistry

1999

vol. 73 nr 4

655-667

Ab-initio gas-phase structure calculation of the geometry of three isomers of the cyanoaniline were determined using the Hartree-Fock level of theory. The optimized molecular structures have been compared with the in-crystal geometry of the molecules. The small differences in the bond lengths and angles were interpreted and analyzed in terms of the distribution of the charge density. The calculated charge density and its Laplacian function were analyzed in terms of the topological properties at the (3,-1) critical points (CPs) of the covalent and polar bonds. The effect of the donor-/acceptor functional groups attached to the phenyl ring is demonstrated especially in the location of the bond critical points and in the charge density at the bond critical points.