A study on synergistic effect of chloride and sulfate ions on copper corrosion by using electrochemical noise in asymmetric cells.

The current study includes a systematic examination of copper corrosion initially in each of NaCl and Na2SO4 solutions separately and then in the mixture solution of Cl- and SO42- ions as aggressive ions. Electrochemical current noise (ECN) signals resulting from asymmetric (Asy) as well as symmetric (Sym) cells have been interpreted using wavelet transform (WT) along with statistical procedures. The signals have been detrended and the decomposition of every signal has been carried out into 8 crystals. Then the standard deviation of every crystal has been illustrated with the standard deviation of partial signal (SDPS) plots. The Asy electrodes increased the pitting detection on copper compared with the Sym ones, indicating higher efficiency of the Asy electrodes. Asymmetric-copper electrodes have been studied using SDPS plots at different temperatures (40, 60, as well as 80 °C). Finally, in order to partly understand the effect of Cl- and SO42- ions on the corrosion of copper, the stabilization of Cu2+ cations by Cl- and SO42- ions in aqueous solutions have been modeled by DFT calculations. The derived results are in accordance with the experimental data.

Investigation of the mechanism of enantioseparation of some drug compounds by considering the mobile phase in HPLC by molecular dynamics simulation.

The separation mechanism of chiral drugs in high-pressure liquid chromatography is yet ambiguous. Computational chemistry helps to gain insights about chiral drug separations. The interaction between the 13 drug enantiomers and cellulose tris (3, 5-dimethyl phenyl carbamate) (chiral cel OD) as chiral stationary phase in 3 mobile phases was assayed by AutoDock and LAMMPS simulations. It is found that not only the structure of 2 enantiomers but also the mobile phase has an important role in enantioseparations and sometimes may invert the elution order. The molecular dynamics simulation is a comprehensive method that can be used to investigate the chiral drug enantioseparation mechanism in HPLC.

Multichannel Gas-Phase Unimolecular Decomposition of Acetone: Theoretical Kinetic Studies.

The multichannel thermal decomposition of acetone is studied theoretically. The isomerization of acetone molecule to its enol form, 1-propene-2-ol, is of especial interest in this research. Steady-state approximation is applied to the thermally activated species CH3COCH3* and CH2C(CH3)OH*, and by performing some statistical mechanical manipulations, integral expressions for the rate constants for the formation of different products are derived. The geometries of the reactant, intermediates, transition states, and products of the reaction are optimized at the MP2(full)/6-311++G(2d,2p) level of theory. More accurate energies are evaluated by single-point energy calculations at the CBS-Q, G4, and CCSD(T,full)/augh-cc-pVTZ+2df levels of theory. In order to account correctly for vibrational anharmonicities and tunneling effects, microcanonical rate constants for various channels are computed by using semiclassical transition state theory. It is found that the isomerization of CH3COCH3 to the enol form CH2C(CH3)OH plays an important role in the unimolecular decomposition reaction of CH3COCH3. The possible products originating from unimolecular decomposition of CH3COCH3 and CH2C(CH3)OH are investigated. It is revealed from present computed rate coefficients that the dominant product channel is the formation of CH2C(CH3)OH at low temperatures and high pressures due to the low barrier height for the isomerization process CH3COCH3 → CH2C(CH3)OH. However, at high temperatures and low pressures, the product channel CH3 + CH3CO becomes dominant. Also, the roaming product channels CH2CO + CH4 and C2H6 + CO could be important at high temperatures.

Theoretical Studies on the Kinetics of Multi-Channel Gas-Phase Unimolecular Decomposition of Acetaldehyde.

Theoretical kinetic studies are performed on the multichannel thermal decomposition of acetaldehyde. The geometries of the stationary points on the potential energy surface of the reaction are optimized at the MP2(full)/6-311++G(2d,2p) level of theory. More accurate energies are obtained by single point energy calculations at the CCSD(T,full)/augh-cc-pVTZ+2df, CBS-Q and G4 levels of theory. Here, by application of steady-state approximation to the thermally activated species CH3CHO* and CH2CHOH* and performance of statistical mechanical manipulations, expressions for the rate constants for different product channels are derived. Special attempts are made to compute accurate energy-specific rate coefficients for different channels by using semiclassical transition state theory. It is found that the isomerization of CH3CHO to the enol-form CH2CHOH plays a significant role in the unimolecular reaction of CH3CHO. The possible products of the reaction are formed via unimolecular decomposition of CH3CHO and CH2CHOH. The computed rate coefficients reveal that the dominant channel at low temperatures and high pressures is the formation of CH2CHOH due to the low barrier height for CH3CHO → CH2CHOH isomerization process. However, at high temperatures, the product channel CH3 + CHO becomes dominant.

Theoretical studies on the kinetics of hydrogen abstraction reactions of H and CH3 radicals from CH3OCH3 and some of their H/D isotopologues.

The hydrogen abstraction reactions by H and CH3 radicals from CH3OCH3 and some of their H/D isotopologues are studied by semiclassical transition state theory. Many high-level density functional, ab initio, and combinatory quantum chemical methods, including B3LYP, BB1K, MP2, MP4, CCSD(T), CBS-Q, and G4 methods, are employed to compute the energies and rovibrational properties of the stationary points for the title reactions. Xij vibrational anharmonicity coefficients, used in semiclassical transition state theory, are computed at the B3LYP, BB1K, and MP2 levels of theory. Thermal rate coefficients and kinetic isotope effects are computed over the temperature range from 200 to 2500 K and compared with available experimental data. The computed rate constants for the title reactions are represented as the equation k(T) = ATn exp[−E(T + T0)/(T2 + T02)].

Theoretical kinetics studies on the reaction of CF3CF═CF2 with hydroxyl radical.

The potential energy surface for the reaction of hexafluoropropene with hydroxyl radical is explored by using BB1K density functional method. Single-point energy calculations are performed at CBS-Q level of theory. Semiclassical transition state theory and a modified strong collision/RRKM model are employed to calculate the thermal rate coefficients for the formation of major products as a function of temperature and pressure. It is revealed from the computed rate constants that the major product channels at low temperatures and high pressures are the formation of the primary adducts formed through OH addition to the double bond of CF3═CFCF2. At high temperatures and low pressures, however, many products arising from unimolecular decomposition of the chemically activated intermediates become important. P9A (CF3CFCOF + HF) and P7B (CF3COCF2 + HF) are dominant products at elevated temperatures. Semiclassical transition state theory is used to compute the overall high-pressure rate constants over the temperature range of 200-1500 K. The computed rate constants are in accordance with the available experimental data.

A new tridentate Schiff base Cu(II) complex: synthesis, experimental and theoretical studies on its crystal structure, FT-IR and UV-Visible spectra.

A new Cu(II) complex [Cu(L)(NCS)] has been synthesized, using 1-(N-salicylideneimino)-2-(N,N-methyl)-aminoethane as tridentate ONN donor Schiff base ligand (HL). The dark green crystals of the compound are used for single-crystal X-ray analysis and measuring Fourier Transform Infrared (FT-IR) and UV-Visible spectra. Electronic structure calculations at the B3LYP and MP2 levels of theory are performed to optimize the molecular geometry and to calculate the UV-Visible and FT-IR spectra of the compound. Vibrational assignments and analysis of the fundamental modes of the compound are performed. Time-dependent density functional theory (TD-DFT) method is used to calculate the electronic transitions of the complex. A scaling factor of 1.015 is obtained for vibrational frequencies computed at the B3LYP level using basis sets 6-311G(d,p). It is found that solvent has a profound effect on the electronic absorption spectrum. The UV-Visible spectrum of the complex recorded in DMSO and DMF solution can be correctly predicted by a model in which DMSO and DMF molecules are coordinated to the central Cu atom via their oxygen atoms.

A novel tridentate Schiff base dioxo-molybdenum(VI) complex: synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, ¹H NMR and ¹³C NMR spectra.

A new dioxo-molybdenum(VI) complex [MoO(2)(L)(H(2)O)] has been synthesized, using 5-methoxy 2-[(2-hydroxypropylimino)methyl]phenol as tridentate ONO donor Schiff base ligand (H(2)L) and MoO(2)(acac)(2). The yellow crystals of the compound are used for single-crystal X-ray analysis and measuring Fourier Transform Infrared (FTIR), UV-visible, (1)H NMR and (13)C NMR spectra. Electronic structure calculations at the B3LYP and PW91PW91 levels of theory are performed to optimize the molecular geometry and to calculate the UV-visible, FTIR, (1)H NMR and (13)C NMR spectra of the compound. Vibrational assignments and analysis of the fundamental modes of the compound are performed. Time-dependent density functional theory (TDDFT) method is used to calculate the electronic transitions of the complex. All theoretical methods can well reproduce the structure of the compound. The (1)H NMR shielding tensors computed at the B3LYP/DGDZVP level of theory is in agreement with experimental (1)H NMR spectra. However, the (13)C NMR shielding tensors computed at the B3LYP level, employing a combined basis set of DGDZVP for Mo and 6-31+G(2df,p) for other atoms, are in better agreement with experimental (13)C NMR spectra. The electronic transitions calculated at the B3LYP/DGDZVP level by using TD-DFT method is in accordance with the observed UV-visible spectrum of the compound.

A new Schiff base compound N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone): synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, 1H NMR and 13C NMR spectra.

The Schiff base compound, N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone) (NDHA) is synthesized through the condensation of 2-hydroxylacetophenone and 2,2-dimethyl 1,3-amino propane in methanol at ambient temperature. The yellow crystalline precipitate is used for X-ray single-crystal determination and measuring Fourier transform infrared (FTIR), UV-visible, (1)H NMR and (13)C NMR spectra. Electronic structure calculations at the B3LYP, PBEPBE and PW91PW91 levels of theory are performed to optimize the molecular geometry and to calculate the FTIR, (1)H NMR and (13)C NMR spectra of the compound. Time-dependent density functional theory (TDDFT) method is used to calculate the UV-visible spectrum of NDHA. Vibrational frequencies are determined experimentally and compared with those obtained theoretically. Vibrational assignments and analysis of the fundamental modes of the compound are also performed. All theoretical methods can well reproduce the structure of the compound. The (1)H NMR and (13)C NMR chemical shifts calculated by all DFT methods are consistent with the experimental data. However, the NMR shielding tensors computed at the B3LYP/6-31+G(d,p) level of theory are in better agreement with experimental (1)H NMR and (13)C NMR spectra. The electronic absorption spectrum calculated at the B3LYP/6-31+G(d,p) level by using TD-DFT method is in accordance with the observed UV-visible spectrum of NDHA. In addition, some quantum descriptors of the molecule are calculated and conformational analysis is performed and the results were compared with the crystallographic data.

Quantum chemical and theoretical kinetics study of the O(3P) + CS2 reaction.

The triplet potential energy surface of the O((3)P) + CS(2) reaction is investigated by using various quantum chemical methods including CCSD(T), QCISD(T), CCSD, QCISD, G3B3, MPWB1K, BB1K, MP2, and B3LYP. The thermal rate coefficients for the formation of three major products, CS + SO ((3)Σ(-)), OCS + S ((3)P) and CO + S(2) ((3)Σ(-)(g)) were computed by using transition state and RRKM statistical rate theories over the temperature range of 200-2000 K. The computed k(SO + CS) by using high-level quantum chemical methods is in accordance with the available experimental data. The calculated rate coefficients for the formation of OCS + S ((3)P) and CO + S(2) ((3)Σ(-)(g)) are much lower than k(SO + CS); hence, it is predicted that these two product channels do not contribute significantly to the overall rate coefficient.

A new salen base 5-(phenylazo)-N-(2-amino pyridine) salicyliden Schiff base ligand: synthesis, experimental and density functional studies on its crystal structure, FTIR, 1H NMR and 13C NMR spectra.

A novel Schiff base ligand 5-(phenylazo)-N-(2-amino pyridine) salicyliden is prepared through the condensation of 5-(phenylazo) salicylaldehyde and 2-amino pyridine in methanol at room temperature. The orange crystalline precipitate is used for X-ray crystallography and measuring Fourier transform (FTIR), 1H NMR and 13C NMR spectra. Density functional theory (DFT) calculations at the B3LYP, MPWB1K and B3PW91 levels of theory is used to optimize the geometry and calculate the FTIR, 1H NMR and 13C NMR spectra of the compound. The vibrational frequencies determined experimentally are compared with those obtained theoretically and a vibrational assignment and analysis of the fundamental modes of the compound is performed. We found that the MPWB1K method predicts low vibrational frequencies better than the commonly used B3LYP method. Although the B3PW91 method overestimates the 1H NMR chemical shifts, the values computed at the B3LYP level of theory are in accordance with experimental 1H NMR spectrum. However, both B3LYP and B3PW91 methods tend to overestimate 13C NMR chemical shifts. In addition, a few quantum descriptors of the molecule are calculated and conformational analysis is performed and the result was compared with crystallographic data.