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Principal component analysis was used in the selection of the B3PW91/6-311+G(3df) method for calculations of As2O3 molecular species. This multivariate analysis compared experimental properties (structure and ionization energy) of As4O6 molecule with several computational methods (Hartree-Fock, second-order Møller-Plesset perturbation theory, and density functional theory) and basis sets. At the selected level of theory, we were able to calculate nine structures of As2O3 with three of them being stable ones (no negative force constants) in the following stability order: D3H (0.0), DIAMOND OUT (32.77 kJ mol−1), and GAUCHE (43.81 kJ mol−1). Several intramolecular conversions were studied with the GAUCHE → DIAMOND OUT transformation being barrierless, whereas the DIAMOND OUT structure is converted into the D3H isomer through a Gibbs free-energy barrier of 40.83 kJ mol−1. Starting from the GAUCHE structure of As2O3 and its enantiomeric form, it was possible to obtain directly (barrierless) the As4O6 species in a spontaneous process (Δr G = −399.92 kJ mol−1 at 298 K and 1 atm) in gas phase. Thus, the As4O6 species is probably the precursor of arsenic hydroxide through hydrolysis reactions. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The chemical compound hydantoin is commonly used in the synthesis of broad-spectrum medicaments with multiple pharmacological activities. There are several papers in literature describing hydantoin derivates, yet few are related to the isolated molecule. In this work, we have performed B3LYP and MP2 calculations with the 6-31++G(d,p) basis set in order to obtain the geometric, energetic, and electronic parameters of the isolated hydantoin and its dimers. We have performed a complete energetic analysis of these complexes considering corrections from the basis set superposition error ( BSSE) and zero-point energy (ZPE) approaches. On the basis of these results, we have proposed and tested an additive model which has successfully predicted the complexation energies of larges hydantoin complexes. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Abstract: MP2/6-31++G(d,p) ab initio calculations have been performed to estimate the effect of the H-bond on the vibrational properties of HF due to its complexation with aromatic azines (C n N6-n H n , with n =5, 4 or 3). Our calculations have revealed that the greater is the number of nitrogen atoms in the aromatic ring, the smaller will be the HF stretching frequency downward shift and the increase of the H–F stretching intensity due to complexation. For example, the H–F frequency downward shift is 899cm−1 in pyridine-HF, whereas its corresponding value is 597cm−1 in 1,3,5-triazine-HF. Their infrared intensity ratios between the complexes and their corresponding monomers are 18.7 and 14.3cm−1, respectively. We have found a relationship between the HF stretching frequency downward shift and the number and position of the nitrogen atoms in the aromatic ring. As expected, the HF stretching intensity is enormously increased upon complexation and its value can be predicted by using the ∂P z /∂z H element of the hydrogen polar tensor, where z is the Cartesian axis along the H–F chemical bond. [Copyright &y& Elsevier]