Computational Chemistry

The vibrational properties of 2–methyl-6-nitroquinoline have been investigated by FTIR and FT–Raman spectroscopies were performed according to the SQM force field method based on DFT calculation at the B3LYP/6-311+G(d,p) level. The assignments of the most of the fundamentals of the title compound provided in this work are quite comparable and unambiguous. The results confirm the ability of the methodology applied for interpretation of the vibrational spectra of the title compound in the solid phase.

Computational chemistry is rapidly emerging as a new branch of chemistry. It is basically the application of chemical, mathematical, and information technology principles to the solution of complex chemical problems. It uses computers to the 3-dimensional structures and key properties of molecules and materials. This information can provide critical insight and better mechanistic understanding of complex chemical systems, leading to discovery and development new materials with superior properties. Computational chemistry is widely used in many multidisciplinary fields with applications in chemistry, biology, and material science. This paper provides a brief introduction to computational chemistry.

If a nuclear reactor happened to be prompt critical - even very slightly - the number of neutrons would increase exponentially at a high rate, and very quickly the reactor would become uncontrollable by means of cybernetics. The prompt neutron flux spectrum of the compact core of the Ghana’s miniature neutron source reactor (MNSR) was understudy using the Monte Carlo method. 20484 energy groups combined for all three categories of the energy distribution, thermal, slowing down and fast regions were modeled to create small energy bins. The moderator, the inner irradiation channels, the annulus beryllium reflector and the outer irradiation channels were the region monitored. The prompt thermal neutrons recorded it highest flux in the inner irradiation channel with a peak flux of (1.2091 ± 0.0008) × 1012 n/cm2•s, followed by the outer irradiation channel with a peak flux of (7.9393 0.0056) × 1011 n/cm2•s. The beryllium reflector recorded the lowest flux in the thermal region with a peak flux of (2.3328 0.0004) × 1011 n/cm2•s. The peak values of the thermal energy range occurred in the energy range 1.8939× 10-08 MeV – 3.7880× 10-08 MeV. The inner irradiation channel again recorded the highest flux of (1.8361 0.0301) × 1009 n/cm2•s at the lower energy end of the slowing down region between 8.2491× 10-01 MeV – 8.2680 × 10-01 MeV, but was over taken by the moderator as the neutron energies increase to 2.0465 MeV. The outer irradiation channel recorded the lowest flux in this region. In the fast region, the core, where the moderator is found, the moderator recorded the highest flux as expected at a peak flux of (2.9143 0.0195) × 1008 n/cm2•s at 6.961MeV. The inner irradiation channel recorded the second highest flux while the outer channel and annulus beryllium recorded very low flux in this region. The final k-effective contribution from only prompt neutrons is 0.9956, hence the Ghana MNSR not prompt critical

The corrosion inhibition and adsorption processes of L - METHIONINE SULFONE (LMS) on mild steel in 2 HCl was studied by means of chemical (weight loss), electrochemical and quantum chemical techniques. The inhibition efficiency increases with decreasing temperature and increasing concentration of inhibitor. It has been determined that the adsorption of LMS on mild steel obeys the Temkin adsorption isotherm at all studied temperatures with negative values of ?Goads, suggesting a stable and a spontaneous inhibition process. In potentiodynamic polarization, the curves shifted towards lower current density in the presence of LMS with well-defined Tafel regions suggesting that the inhibitor retard the corrosion process without changing the mechanism of the corrosion process; and exhibit cathodic and anodic polarization (mixed type inhibitors) because the change in Ecorr is less than 85 vM/SCE with respect to the blank. Corrosion current density was calculated by extrapolation of the linear parts of these curves to the corresponding corrosion potential; and corrosion potential (Ecorr), corrosion current densities (icorr), anodic Tafel slope (?a), cathodic Tafel slope (?b) were determined with maximum value of inhibition efficiency for 5 x 10-4 M concentration of the inhibitor at 303 K is 75.1%. From Nyquist plots of electrochemical impedance spectroscopy, value of polarization resistance (Rp) increased with increasing inhibitor concentration whereas double layer capacitance (Cdl) decreased indicating a decrease in local dielectric constant or an increase in thickness of electric double layer suggesting that the inhibitors function by forming a protective layer at the metal surface. Inhibition efficiency value (? %) is 55.9%. Quantum chemical calculations were performed using Density Functional Theory (DFT) with the help of complete geometry optimization for theoretical calculations of EHOMO, ELUMO, and energy gap (?E). Inhibition efficiency increases with increasing EHOMO indicating that the molecule has tendency to donate electrons to the appropriate acceptor molecule with low energy empty molecular orbital; whereas low value of ELUMO suggests that the molecule easily accepts electrons from donor molecules.

The adsorption of mercuric ions (Hg2+) on nano zinc oxide (ZnO-NPs) structure was studied using the Monte Carlo simulation and the density functional theory (DFT) methods. The obtained results have shown that the adsorption process is thermodynamically favorable. The mercuric ions are strongly adsorbed on the ZnO-NPs structures due to the formation of the chemical bonds resulted from the positive overlap between p-orbitals of the adsorbate species and the p-orbitals of the zinc atoms in the structure of ZnO-NPs.

The structurally similar cresol derivatives of o-cresol, m-cresol and p-cresol were characterized by FT-IR, FT-Raman experimental techniques, ab initio Hartree-Fock (HF) and density functional theoretical (DFT) calculations. The calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution (PED). The comparisons and assignments of vibrational frequencies indicate that, the experimental spectra coincide satisfactorily with those of theoretically simulated spectrograms. The calculated HOMO and LUMO energies show the charge transfer occurs within the molecule. The charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESPs).

Quantum chemical calculations of energies, geometrical structures and electronic absorption spectra of 3,5-diamino-1,2,4-triazole (DAT) were carried out by ab initio HF/6-311+G(d,p), DFT (B3LYP/6-311+G(d,p)). The optimized geometric bond lengths and bond angles obtained by HF method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of DAT with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the FT-IR and FT- Raman, NMR spectra of DAT was also reported. Thermodynamic properties were also calculated and discussed. UV–vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra. The Mulliken charge analysis indicates that the nitrogen atoms of the triazole ring and the amino group attached to the ring are the main reactive centers of 3,5-diamino-1,2,4-triazole. And the temperature dependence of the thermodynamic properties of constant pressure (Cp), entropy (S) and enthalpy change (?H0?T) for DAT were also determined.

The Dilute solution viscometric (DSV) technique is employed to find the molecular interactions between the non-Newtonian Doxycycline hyclate and the essential unsaturated fatty acid, Ricinoleic acid in the common solvent Ethyl methyl ketone. The viscometric parameters as improved by chee and Sun et. al., identifies the molecular interactions at physiological temperatures. The conformity of interaction is attempted by the ultrasonic velocity; and the related acoustical parameters at temperatures 303, 310 and 313K. The behaviour of these parameters explains the molecular interactions on the basis of solute-solute and solute-solvent interactions.

Theoretical studies were conducted on the molecular structure and vibrational spectra of 2-methoxy-6-methyl pyridine (MMP). The FT-IR and FT-Raman spectra of MMP were recorded in the solid phase. The molecular geometry and vibrational frequencies of MMP in the ground state have been calculated by using the ab initio HF (Hartree-Fock) /6-311+G(d,p) and density functional methods (B3LYP) invoking 6-311+G(d,p)/6-311++G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of MMP with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the FT-IR and FT- Raman, NMR spectra of MMP was also reported. NBO analysis has been performed in order to elucidate charge transfers or conjugative interaction, the intra-molecule rehybridization and delocalization of electron density within the molecule. UV–vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra.

This work deals with the vibrational spectroscopy of Hexafluorobenzene (HFB) by means of quantum chemical calculations. The FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP / 6-311+G** basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled quantum mechanical force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra.