The formation of interstellar organic molecules: H2C3O A DFT and ELF theoretical study

This quantum study at B3LYP/6-311 ++ G (d, p) with ELF analysis were performed in order to understand the formation of propynal and cyclopropenone, two molecules detected in the interstellar medium. The formation of these molecules is supposed to be through reactions between carbon monoxide (CO) and acetylene (C2H2) in the cold conditions of interstellar clouds. All the structures, reagents, products and transition states, have been optimized and the geometrical parameters are given as well as the dipole moments. The reaction paths are elaborated and discussed here using the IRC method implemented in the Gaussian program. The determined activation energies allow an estimation of the rate constants. The ELF analysis performed here seems to be a valuable tool for screening the evolution of the bonds during the formation processes. The two reactions probably occur in one step. The propadienone, another possible isomer, has been also studied. It is formed through a third reaction. A stable triplet ground state of this molecule, the thermodynamic consideration and a small dipole moment can explain the fact that it is not detected yet in the interstellar medium. M06-2X and WB97XD functional were also used for comparing results.

Liquid Crystalline Properties of 4,4and#39;-methylenebis(N-(4-Alkanoxybenzylidene)aniline): Synthesis, Characterization, and Theoretical study

The paper presents six homologues series of Schiff bases ether compounds distinguished by the length of terminal alkoxy groups which substituted on a side benzene nucleus. The above structures were demonstrated through the use of spectroscopic techniques, like FT- IR and 1H-NMR. Polarized hot stage optical microscopy was used to study both mesomorphic properties and phase transitions. The results showed that out of the six compounds only three (B2, B3 and B4) were pure (marble) nematic mesophase, while no liquid crystal properties for (B5, B6 and B7) compounds. The theoretical study for the electronic structures was intended to study the effects of alkyl chain length on the electronic structure by using Gaussian program, DFT and 6-31G as basis set. The theoretical results indicate that there is no effect to the terminal substituted alkoxy groups on the HOMO energies but there is an effect on LUMO energies through decreasing energy for the prepared compounds.

Spectral and Thermal Studies of Some Nucleic Acid Complexes

Barbituric acid, thiobarbituric acid and thiouracil complexes with sodium and potassium chlorides were prepared and characterized by UV in different solvents and IR experimentally and theoretically using B3LYP method and Gaussian program. The composition of the studied complexes was also confirmed by elemental and thermal analysis, TG, DTA and DSC techniques to determine thermodynamic parameters (Ea, ΔH, ΔS and ΔG). The negative value of entropy of activation indicated the fragments have ordered structures than undecomposed complexes. The positive values of enthalpy of activation of the decomposition stages indicated that the process is endothermic. The positive values of free energy of the decomposition indicated non-spontaneous process. Evaluation of kinetics parameters were done. The isokinetic temperature β is 407 K, which is lower than experimental temperature range, confirming the processes is entropy control. However, the plots of ΔH versus ΔS for the complexes under investigation gave straight line indicating a close similarity in the mechanism.

Synthesis, Characterization and DFT Study of 4,4′-Oxydianiline Imines as Precursors of Tetrahalo-1,3-oxazepine-1,5-dione

This work presents four Schiff bases derived from 4,4′-Oxydianiline, distinguished by the para substituted halogen of benzaldehyde. These bases were used to synthesize eight compounds of di-1,3-oxazepine by direct condensation with tetrachloro phthalic anhydride and tetrabromo phthalic anhydride. The reactions were monitored with TLC and all structures were characterized using spectroscopic techniques such as FT-IR, 1H-NMR, 13C-NMR and C, H, N techniques. On the other hand, a theoretical study by Density Functional Theory (DFT) for the electronic structures was intended to study the effects of para-substituted halogen of benzaldehyde on the electronic structure of synthesized Schiff bases by using the Gaussian program. Theoretical results indicate that there is no effect of halogen atoms except for bromine on HOMO and LUMO energies of the synthesized compounds.

Complexes of Some Transition Metal with 2-Benzoyl thiobenzimidazole and 1,10-Phenanthroline and Studying their Antibacterial Activity

Mixed ligands of 2-benzoyl Thiobenzimiazole (L1) with 1,10-phenanthroline (L2) complexes of Cr(III) , Ni(II) and Cu(II) ions were prepared. The ligand and the complexes were isolated and characterized in solid state by using FT-IR, UV-Vis spectroscopy, 1H, 13C-NMR, flame atomic absorption, elemental micro analysis C.H.N.S, magnetic susceptibility , melting points and conductivity measurements. 2-Benzoyl thiobenzimiazole behaves as bidenetate through oxygen atom of carbonyl group and nitrogen atom of imine group. From the analyses Octahedral geometry was suggested for all prepared complexes. A theoretical treatment of ligands and their metal complexes in gas phase were studied using HyperChem-8 program, moreover, ligands in gas phase also has been studied using Gaussian program (GaussView Currently Available Version (5.0.9) along with Gaussian 09 which was the latest in the Gaussian series of programs). The antibacterial activity of the prepared complexes have been determined and compared with that of the ligand and the standard metronidazole.

Theoretical Study for Potential Energy Curves, Dissociation Energy and Molecular Properties for (LiH, H2, HF) Molecules

A theoretical study has been carried out of calculating dissociation energies and potential energy curves (Deng-Fan potential and Varshni potential) and molecular parameters of of ground state of diatomic molecules (LiH, H2, HF). Dissociation energies and potential energy curves depended on spectroscopic constants (ωe, ωexe, re, α, μ, β ,) and our results has been compared with experimental results. Molecular and electronic properties as εHOMO, εLUMO, ionization potentials (IP), electron affinities (EA) and binding energy was performed by using B3P86/6-311++g** method and Gaussian program 03, the results is well in a agreement with that of other researchers.

Thermodynamics Study of Removal of Heavy Metal by TiN-Nanotubes

The ability of TiN -nanotube to remove lead ( Pb ( II )) and arsenic ( As ( III )) ions from aqueous solutions is investigated. The thermodynamics properties of Pb ( II ) and As ( III ) ions passing through TiN -nanotubes ( TiN - NTs ) is calculated in basis set (B3LYP/6-31G**) DFT-IR method by Gaussian program package. The results showed, Pb ( II ) and As ( III ) passing through had low potential in middle nanotubes, and are trapped in this place. The thermodynamic properties showed; the passing through are spontaneous and favorable because ΔGele (MJ/mol) is negative for them. The goal of this study is the detection of surface species of TiN - NTs for metal ions removal by using computer calculations. The structural and thermodynamic properties studied ions absorption on TiN - NTs at room temperature.

Investigation of structure and vibrational properties of cyclobutane pirimidine dimer

We performed a theoretical analysis of the structure and vibrational properties of cyclobutane pyrimidine dimer, which is the main product in a photochemical reaction involving two molecules of 1-methylthymine. Thymine is a pyrimidine base that has the highest yield of the dimerization photoproducts. Methylation in position one was chosen because in this position thymine is linked to sugar in DNA. The calculations were performed at the B3LYP/cc-pVTZ level with a Gaussian program package. All molecular geometries were optimized without symmetry constraints in vacuum and D2O. Vibrational frequencies were calculated in the harmonic approximation. It was shown that there are two stable isomers, CPD(cis-syn) and CPD(trans-syn). CPD(trans-syn) is more stable both in vacuum and in D2O. By dissolving these molecules in D2O, both structures become more stable, although the stabilization of the less stable isomer is more pronounced due to its larger dipole moment. Thus, the difference in stability of the two isomers in D2O is almost two times lower than in vacuum. Because of the similarity of the two isomers? structures, the difference in their vibrational spectra is not pronounced. Within the harmonic approximation, there is only a slight difference in the C=O and C-H stretching region. The difference in the N-H stretching region is more pronounced; in the CPD(cis-syn) molecule the two bonds vibrate separately, whereas in the CPD(trans-syn) the two modes couple, and this coupling results in symmetric and asymmetric N-H stretching. The observation shows that a slight difference in geometry can be reflected in the shape of the infrared spectra. A more detailed analysis of the vibrational properties would involve computation of anharmonic coupling terms, which would enable a more precise determination of the peak positions.

Absence of Conjugation in Vibrational Spectra and Assignments of Dichloro(vinyl)phosphine and Dichloro(phenyl)phosphine Oxides and Sulfides

The structure and conformational stability of dichloro(vinyl)phosphine and dichloro(phenyl)- phosphine oxides and sulfides were investigated using calculations at the DFT/6-311G** and ab initio ones at the MP2/6-311G** level. We know from our previous results that the addition of diffuse functions to a valence triple zeta basis with polarization functions might lead to an unbalanced basis, which performs even worse than the smaller basis without diffuse functions, as it is the case for the 6-311++G** basis set in the Gaussian program. For large energy differences between conformers, DFT works very well, in some cases even better than MP3 or MP4. The vinyl derivatives were predicted to exist in a cis/gauche conformational equilibrium with cis (the PX bond, X being oxygen or sulfur eclipses the vinyl groups) being the predominant conformer at ambient temperature. In the phenyl case case the two planar forms are equivalent minima. The asymmetric potential function for the internal rotation was determined for each of the molecules. The vibrational frequencies were computed and the spectra, where possible, were compared with the experimental ones. Normal coordinate calculations were carried out and potential energy distributions were calculated for the molecules in the cis and gauche conformations (in the vinyl case, planar one for phenyl), providing a complete assignment of the vibrational lines to symmetry coordinates in the molecules. From our results and their analysis we conclude, in agreement with literature results based on localized orbitals, that conjugation effects are absent - or at least negligible - as compared with electrostatic ones in determining the structures of the stable conformers in both the vinyl and the phenyl derivatives. The P-O bond should be a highly polarized triple bond, as confirmed by analysis of Mulliken populations. The polarization turned out to be much less in the sufides due to the much smaller electronegativity of sulfur as compared with oxygen.