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Peter Poliak

Abstract

The theoretical pKa values of the derivatives of anilinium and pyridinium ions in 7 solvents are presented. For this purpose, the usage of isodesmic reaction scheme using the DFT/B3LYP approach with IEFPCM solvation was evaluated. We have shown that the suitable selection of reference species has the primary influence on the resulting data. For the studied anilinium ion derivatives the nonsubstituted anilinium ion seems to be a satisfactory reference system. The calculated values are in good accordance with the available experimental data with the RMS error of 1.00 and 0.99 pKa units in water and THF, respectively. The highest error in predicted pKa value is less than 2.0 pKa units in all cases. The chemical accuracy of the applied treatment is limited in the case of nitroaniline ions and the maximal therotetical uncertainty for derivatives of the pyridinium ion is within 2.1 pKa units. Our theoretical results enable us to predict the values of pKa for the solvents, where the experimental data are not completely available. Also the influence of the chemical structure on the accuracy of the applied method was discussed.

Open access

Peter Poliak and Adam Vagánek

Abstract

In this work, the influence of the inter-ring dihedral angles and their deformation on the energetics of diphenylamine molecule and its radical is investigated by the B3LYP/6-311++G** approach. Our approximated bond dissociation enthalpy of diphenylamine is 370.0 kJ mol-1 and it is in good agreement with the recently published experimental data. The potential functions of both the molecule and the radical with respect to the mutual aromatic ring orientations are presented. The potential function for the molecule is of a double-barrier type, whereas the radical possesses a single-barrier function. The calculated total electronic energies are used to approximate the change of the bond dissociation enthalpy with the twisting of the dihedral angle. The dependence of the bond dissociation enthalpy on the dihedral angle is represented by a single-barrier type function. The dependence of the nitrogen atom spin density on the studied dihedral angle is also discussed.

Open access

Martin Michalík, Peter Poliak and Vladimír Lukeš

Abstract

The substituent effect on the geometry and strain enthalpy of [2,2]paracyclophane is theoretically investigated by density functional theory. Gas-phase calculations were performed for twenty distinct electron donating and electron withdrawing substituents. The largest out-of-plane distortion of phenyl rings is exhibited by —SCN and —CF3 groups. On the other hand, —OH, —CH3 and —F groups show the minimal deformation. The strain enthalpy for unsubstituted [2,2]paracyclophane associated with repulsive forces between phenyl units reached up to 118.5 kJ mol−1. Any substitution causes increase of the strain enthalpy value proportionally to the absolute values of Hammett para-substituent constants. Two separate linear dependences with similar slopes were obtained for monosubstituted as well as double symmetrically substituted derivatives.

Open access

Denisa Cagardová, Peter Poliak and Vladimír Lukeš

Abstract

Derivatives of anilide were studied systematically by the density functional theory (DFT) using the B3LYP hybrid functional and the 6-311+G(3df,2p) basis set. Characteristic frequencies of N-H and C=O stretching modes for cis and trans conformers distinguishing were compared with available experimental and theoretical data. Effect of substitution in ortho position and acidic residue group is discussed with respect to the bond length changes in the aromatic ring and aromaticity indexes. Energy differences between cis and trans conformations allow estimating the effect of intramolecular hydrogen bonds stabilizing the studied conformations. The trans conformation of parent formanilide is stabilized via the C(aromatic) -H∙∙∙O=C interaction with the energy of around 4 kJ・mol-1. The selected anilide series represent model compounds for drug design.

Open access

Martin Michalík, Adam Vagánek and Peter Poliak

Abstract

A chemical microsolvation model for solution phase bond dissociation enthalpy (BDE) evaluation by means of molecular dynamics is presented. In this simple model, the primary solvent effect on the BDE values was estimated by placing of five water molecules nearby the studied functional groups evenly. Furthermore, the secondary solvent effect was reflected using the conductor like screening model (COSMO). From the quantum-chemical point of view, the molecular dynamics simulations based on the B3LYP functional in rather small basis set were performed. Despite of the constitutional limitations of the proposed model, the obtained O-H and N-H BDE values in phenol (363 kJ mol-1) and aniline (369 kJ mol-1) are in good agreement with the experimental solution phase data.

Open access

Peter Poliak and Adam Vagánek

Abstract

In this work, C-H bond dissociation enthalpies (BDE) and vertical ionization potentials (IP) for various hydrocarbons and ketones were calculated using four density functional approaches. Calculated BDEs and IPs were correlated with experimental data. The linearity of the corresponding dependences can be considered very good. Comparing two used functionals, B3LYP C-H BDE values are closer to experimental results than PBE0 values for both used basis sets. The 6-31G* basis set employed with both functionals, gives the C-H BDEs closer to the experimental values than the 6-311++G** basis set. Using the obtained linear dependences BDEexp = f (BDEcalc), the experimental values of C-H BDEs for some structurally related compounds can be estimated solely from calculations. As a descriptor of the C-H BDE, the IPs and 13C NMR chemical shifts have been investigated using data obtained from the B3LYP/6-31G* calculations. There is a slight indication of linear correlation between IPs and C-H BDEs in the sets of simple alkanes and alkenes/ cycloalkenes. However, for cycloalkanes and aliphatic carbonyl compounds, no linear correlation was found. In the case of the 13C NMR chemical shifts, the correlation with C-H BDEs can be found for the sets of alkanes and cycloalkanes, but for the other studied molecules, no trends were detected.

Open access

Vojtech Kollár, Jana Gasperová and Peter Poliak

Abstract

Recently we have witnessed declining confidence of citizens in public authorities in developed countries. The paper provides an insight into the tools of e-democracy as a critical component of a developed democracy. We claim that one of the possible reasons for the loss of confidence of the citizens is that the traditional mechanisms of democracy do not often comply with the decision of those who govern. Only the citizens who show interest by watching and following current events, and who know where to look for this information, get to the final output in the form of regulations, decrees, laws, etc. Publication of the outcomes of public administration and governance on their web sites enables to keep track of the news and at the same time, creates a space for the development of the active participation of citizens in the management of public affairs with a feedback.

Open access

Peter Škorňa, Adam Vagánek, Peter Poliak and Erik Klein

Abstract

Gas phase bond dissociation enthalpies (BDE) of para- and meta-substituted benzoic acids and proton affinities (PA) of their carboxylate anions were investigated using the B3LYP/6-311++G** method for 15 substituents with various electron-donating and electron-withdrawing effects. The employed computational method provided BDE and PA values in fair agreement with experimental data. The substituent effect on BDEs and PAs was analyzed in terms of Hammett constants. Found dependences exhibit satisfactory linearity and enable quick estimation of BDEs and PAs from the Hammett constants.