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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]

Abstract: MP2/6-31++G(d,p) and B3LYP/6-31++G(d,p) theoretical calculations have been employed to investigate the hydrogen bonding formation involving the vic-, cis- and trans-C2H2F2 isomers and hydrogen fluoride. Our calculations have revealed for each isomer the preferential existence of two possible hydrogen-bonded complexes: a non-cyclic complex and a cyclic complex. For all the three isomers the binding energies for the non-cyclic and cyclic hydrogen complexes are essentially equal using both the MP2 and B3LYP calculations, being that the cyclic structure is slightly more stable. For instance, the binding energies including BSSE and ZPE corrections for the non-cyclic and cyclic structures of cis-C2H2F···HF are 8.7 and 9.0kJmol−1, respectively, using B3LYP calculations. The cyclic complex formation reduces the polarity, in contrast to what occurs with the non-cyclic complex. This result is more accentuated in vic-C2H2F2···HF. In this latter, Δμ(cyclic) is −3.07D, whereas Δμ(non-cyclic) is +1.92D using B3LYP calculations. Their corresponding MP2 values are +0.44D and −1.89D, respectively. As expected, the complexation produces an Hing frequency downward shift, whereas its IR intensity is enhanced. On the other hand, the vibrational modes of the vic-, cis- and trans-C2H2F2 isomers are little affected by complexation. The new vibrational modes due to hydrogen bonding formation show several interesting features, in particular the HF bending modes which are pure rotations in the free molecule. [Copyright &y& Elsevier]

Abstract: Configurational and conformational analysis were performed using ab initio and semi-empirical molecular orbital methods in order to obtain structural, electronic and energetic information about three previously synthesized imidazolidine derivatives, namely: 3-benzyl-5-benzylidene-imidazolidine-2,4-dione (5), 3-benzyl-5-benzylidene-2-thioxo-imidazolidine-4-one (6), 5-benzylidene-3-(2-oxo-2-phenyl-ethyl)-2-thioxo-imidazolidine-4-one (7) and other two new proposed imidazolidine derivatives: 3-benzyl-5-benzylidene-4-thioxo-imidazolidine-2-one (8) and 3-benzyl-5-benzylidene-imidazolidine-2,4-dithione (9). Important aspects related to structure activity relationship are highlighted. [Copyright &y& Elsevier]