Density functional theory studies of conformational stabilities and rotational barriers of 2- and 3-thiophenecarboxaldehydes

2016 ◽  
Vol 57 (8) ◽  
pp. 1640
Author(s):  
Y. Umar ◽  
J. Tijani ◽  
S. Abdalla
Keyword(s):  
Density Functional ◽  
Dipole Moments ◽  
Structural Parameters ◽  
Conformational Stability ◽  
Energy Difference ◽  
Polarizable Continuum Model ◽  
Molecular Structures ◽  
Basis Set ◽  
Potential Energy Distribution ◽  
Vibrational Wavenumbers

The molecular structures, conformational stabilities, and infrared vibrational wavenumbers of 2-thiophenecarboxaldehyde and 3-thiophenecarboxaldehyde are computed using Becke-3—Lee—Yang—Parr (B3LYP) with the 6-311++G** basis set. From the computations, cis-2-thiophenecarboxaldehyde is found to be more stable than the transfer conformer with an energy difference of 1.22 kcal/mol, while trans-3-thiophenecarboxaldehyde is found to be more stable than the cis conformer by 0.89 kcal/mol. The computed dipole moments, structural parameters, relative stabilities of the conformers and infrared vibrational wavenumbers of the two molecules coherently support the experimental data in the literature. The normal vibrational wavenumbers are characterized in terms of the potential energy distribution using the VEDA4 program. The effect of solvents on the conformational stability of the molecules in nine different solvents is investigated using the polarizable continuum model.

Experimental FTIR and theoretical investigation of the molecular structure and vibrational spectra of acetanilide using DFT and dispersion correction to DFT

2019 ◽  
Vol 18 (02) ◽  
pp. 1950009 ◽  
Author(s):  
Yunusa Umar ◽  
Nedal Abu-Thabit ◽  
Paul Jerabek ◽  
Ponnadurai Ramasami
Keyword(s):  
Vibrational Spectra ◽  
Density Functional ◽  
Decomposition Analysis ◽  
Density Functional Theory Method ◽  
Molecular Structures ◽  
Basis Set ◽  
Potential Energy Distribution ◽  
Energy Decomposition Analysis ◽  
Dispersion Correction ◽  
Vibrational Assignments

The FTIR spectrum of acetanilide (ACN) is recorded and analyzed. The optimized molecular structures, harmonic vibrational wavenumbers and corresponding vibrational assignments of the ACN are computationally examined by using the B3LYP density functional theory method together with the standard 6-311[Formula: see text]G([Formula: see text],[Formula: see text]) basis set. From the calculations, the ACN is predicted to exist predominantly in trans configuration with the relative energy, rotational barrier, and population of 2.8[Formula: see text]kcal/mol, 14.8[Formula: see text]kcal/mol, and 99.5%, respectively. The optimized structure shows that the amide group (CO–NH) of trans-ACN adopts a planar peptide-like conformation. The effect of the incorporation of dispersion correction to the B3LYP on the calculated equilibrium structure and vibrational spectra of ACN is investigated. The highest occupied and the lowest unoccupied molecular orbitals, IR intensities and molecular electrostatic potential results are reported. In addition, reliable vibrational assignments have been made on the basis of Potential Energy Distribution (PED) using VEDA4 program. Simulated IR spectrum are compared with the experimental FTIR and FT-Raman spectra. Energy decomposition analysis (EDA) revealed that Pauli repulsion is responsible for the increased stability of the trans over the cis isomer.

Conformational stability, barriers to internal rotations, and normal coordinate analysis of acetone and its2H-isotopomers

2016 ◽  
Vol 94 (10) ◽  
pp. 818-826 ◽  
Author(s):  
Mahboobeh Gholamhoseinpour ◽  
Sayyed Faramarz Tayyari ◽  
Saeedreza Emamian
Keyword(s):  
Density Functional ◽  
Conformational Stability ◽  
Normal Modes ◽  
Normal Coordinate Analysis ◽  
Basis Set ◽  
Basis Sets ◽  
Potential Energy Distribution ◽  
Normal Coordinate ◽  
Functional Theory ◽  
Vibrational Bands

Molecular structure and vibrational spectra of acetone, acetone-d3, and acetone-d6were investigated by means of ab initio and density functional theory (DFT) calculations. The harmonic and anharmonic vibrational frequencies of the acetone isotopomers were calculated at the B3LYP (using the 6–311++G(3df,3pd) basis set) and B2PLYP (using the 6–31+(2d,p) and 6–311G(2df,p) basis sets) levels. The calculated frequencies and the Raman and infrared (IR) intensities were compared with the experimental results. Excellent agreement between calculated and observed vibrational wavenumbers was obtained. Additionally, a normal coordinate analysis (NCA) was also done by using the normal mode eigenvectors obtained at the B3LYP/6–311++G(3df,3pd) level. All fundamental vibrational bands were assigned to the normal modes with the aid of the potential energy distribution (PED) values obtained from normal coordinate calculations. To study the internal rotation of CH3groups, single CH3rotation and synchronous rotations of both CH3groups (clockwise–clockwise and clockwise–counterclockwise) were analyzed using the MP2/6–311++G(3df,2pd) and B3LYP/6–311++G(3df,2pd) levels.

New bis 1,3,4-oxadiazole derivatives: syntheses, characterizations, computational studies, and antioxidant activities

2018 ◽  
Vol 96 (12) ◽  
pp. 1047-1059 ◽  
Author(s):  
Yasemin Ünver ◽  
Halil Gökce ◽  
Ersan Bektaş ◽  
Fatih Çelik ◽  
İsmail Değirmencioğlu
Keyword(s):  
Density Functional ◽  
Antioxidant Activities ◽  
Dft Method ◽  
Polarizable Continuum Model ◽  
Basis Set ◽  
Spectral Studies ◽  
Reducing Ability ◽  
Oxadiazole Derivatives ◽  
Homo Lumo ◽  
Vibrational Wavenumbers

In this study, two new bis oxadiazole derivatives (2a and 2b) were synthesized. The new compounds were characterized by elemental analyses, IR, 1H NMR, 13C NMR, and mass spectral studies and were tested for their antioxidant activity. According to the results, it was observed that the synthesized compounds (2a and 2b) had a very high activity in both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing ability of plasma (FRAP) tests. The approximate geometries of the compounds 2a and 2b were prepared with GaussView5 visualization program. The optimized molecular geometric parameters, vibrational wavenumbers, UV–vis parameters, and HOMO–LUMO simulations were computed using Gaussian 09W program. The computations were performed at 6-311++G(d,p) basis set using the B3LYP functional in density functional theory (DFT) method. The harmonic vibrational wavenumbers computed in gas phase were scaled with 0.958 (1700–4000 cm−1) and 0.983 (0–1700 cm−1) for the B3LYP/6-311++G(d,p) level. To calculated the UV–vis spectroscopic parameters with TD-DFT method, the compounds 2a and 2b were optimized in DMF and DMSO solvents using the integral equation formalism polarizable continuum model (IEFPCM) method at the B3LYP/6-311++G(d,p) level. The HOMO, LUMO, and UV–vis analyses were studied to interpret intramolecular charge transfers.

Density functional theory, Comparative vibrational spectroscopic studies, HOMO-LUMO, and NBO analysis of Trichloro isocyanuric acid and Trithio cyanuric acid

2015 ◽  
Vol 8 (3) ◽  
pp. 2197-2221
Author(s):  
Theraviyum Chithambarathanu ◽  
M. Darathi ◽  
J. DaisyMagdaline ◽  
S. Gunasekaran
Keyword(s):  
Density Functional ◽  
Cyanuric Acid ◽  
Nbo Analysis ◽  
Basis Set ◽  
Potential Energy Distribution ◽  
Point Energy ◽  
Isocyanuric Acid ◽  
Ft Ir ◽  
Homo Lumo ◽  
Ft Raman

The molecular vibrations of Trichloro isocyanuric acid (C3Cl3N3O3) and Trithio cyanuric acid (C3H3N3S3) have been investigated in polycrystalline sample at room temperature by Fourier Transform Infrared (FT-IR) and FT-Raman spectroscopies in the region 4000-450 cm-1 and 4000-50 cm-1 respectively, which provide a wealth of structural information about the molecules. The spectra are interpreted with the aid of normal co-ordinate analysis following full structure optimization and force field calculations based on density functional theory   (DFT) using standard B3LYP / 6-311++ G (d, p) basis set for investigating the structural and spectroscopic properties. The vibrational frequencies are calculated and the scaled values are compared with experimental FT-IR and FT-Raman spectra. The scaled theoretical wave numbers shows very good agreement with experimental ones. The complete vibrational assignments are performed on the basis of potential energy distribution (PED) of vibrational modes, calculated with scaled quantum (SQM) method. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that change in electron density (ED) in σ* and π* anti-bonding orbitals and second order delocalization   energy (E2) confirm the occurrence of Intra molecular Charge Transfer (ICT) within the molecule. The thermodynamic properties like heat capacity, entropy, enthalpy and zero point energy have been calculated for the molecule. The frontier molecular orbitals have been visualized and the HOMO-LUMO energy gap has been calculated. The Molecular Electrostatic Potential (MEP) analysis reveals the sites for electrophilic attack and nucleophilic reactions in the molecule.

Quantum Mechanical Investigation of Geometrical Structure and Dynamic Behavior of h-BNNT (9,9-5) and h-AlNNT (9,9-5)Single-Walled Nanotubes: NBO Analysis

2019 ◽  
Vol 16 (9) ◽  
pp. 705-717
Author(s):  
Mehrnoosh Khaleghian ◽  
Fatemeh Azarakhshi
Keyword(s):  
Carbon Nanotubes ◽  
Density Functional ◽  
Structural Parameters ◽  
Energy Levels ◽  
Nbo Analysis ◽  
Electronic Energy ◽  
Boron Nitride Nanotubes ◽  
Basis Set ◽  
B3lyp Method ◽  
Mechanical Investigation

In the present research, B45H36N45 Born Nitride (9,9) nanotube (BNNT) and Al45H36N45 Aluminum nitride (9,9) nanotube (AlNNT) have been studied, both having the same length of 5 angstroms. The main reason for choosing boron nitride nanotubes is their interesting properties compared with carbon nanotubes. For example, resistance to oxidation at high temperatures, chemical and thermal stability higher rather than carbon nanotubes and conductivity in these nanotubes, unlike carbon nanotubes, does not depend on the type of nanotube chirality. The method used in this study is the density functional theory (DFT) at Becke3, Lee-Yang-Parr (B3LYP) method and 6-31G* basis set for all the calculations. At first, the samples were simulated and then the optimized structure was obtained using Gaussian 09 software. The structural parameters of each nanotube were determined in 5 layers. Frequency calculations in order to extract the thermodynamic parameters and natural bond orbital (NBO) calculations have been performed to evaluate the electron density and electrostatic environment of different layers, energy levels and related parameters, such as ionization energy and electronic energy, bond gap energy and the share of hybrid orbitals of different layers.

scholarly journals Photochemistry of 1-Phenyl-4-Allyl-Tetrazol-5-One: A Theoretical Study Contribution towards Mechanism Elucidation

2021 ◽  
Vol 11 (9) ◽  
pp. 4045
Author(s):  
Amilcar Duque-Prata ◽  
Carlos Serpa ◽  
Pedro J. S. B. Caridade
Keyword(s):  
Density Functional ◽  
Reaction Pathway ◽  
Intramolecular Proton Transfer ◽  
Polarizable Continuum Model ◽  
Uv Spectra ◽  
Point Of View ◽  
Basis Set ◽  
Pathway Evolution ◽  
Photodegradation Mechanism ◽  
Energetic Point

The photodegradation mechanism of 1-phenyl-4-allyl-tetrazol-5-one has been studied using (time-dependent) density functional theory with the M06-HF, B3LYP, and PBE0 functionals and the VDZ basis set. All calculations have been carried out using the polarizable continuum model to simulate the solvent effects of methanol. The reaction pathway evolution on the triplet state has been characterised to validate a previously postulated experimental-based mechanism. The transition states and minimums have been initially located by local scanning in partial constrained optimisation, followed by a fully relaxed search procedure. The UV spectra has shown to be better described with PBE0 functional when compared with the experimental results, having the M06-HF a shift of 40 nm. From the energetic point of view, the postulated mechanism has been validated in this work showing a concerted photoextrusion of the N2 molecule. The intramolecular proton transfer occurs at a later stage of the mechanism after cyclization of the allyl group on a triplet biradical intermediate. The photoproduct observed experimentally, a pyrimidinone, has been characterised. The infrared spectroscopic reaction profile has also been proposed.

Systematic ab initio study of the compressibility of silicate garnets

2001 ◽  
Vol 57 (2) ◽  
pp. 163-177 ◽  
Author(s):  
V. Milman ◽  
E. V. Akhmatskaya ◽  
R. H. Nobes ◽  
B. Winkler ◽  
C. J. Pickard ◽  
...  
Keyword(s):  
Experimental Data ◽  
Density Functional ◽  
Structural Parameters ◽  
Applied Pressure ◽  
Basis Set ◽  
Ionic Radii ◽  
Cell Parameters ◽  
The Density Functional Theory ◽  
Dodecahedral Site ◽  
Compression Mechanism

The structural properties of the silicate garnets andradite, Ca3Fe2Si3O12, uvarovite, Ca3Cr2Si3O12, knorringite, Mg3Cr2Si3O12, goldmanite, Ca3V2Si3O12, blythite, Mn^{2+}_3Mn^{3+}_2Si3O12, skiagite, Fe^{2+}_3Fe^{3+}_2Si3O12, calderite, Mn^{2+}_3Fe^{3+}_2Si3O12, and khoharite, Mg3Fe^{3+}_2Si3O12, have been investigated with a quantum-mechanical model as a function of applied pressure. The study has been performed with the density functional theory code CASTEP, which uses pseudopotentials and a plane-wave basis set. All structural parameters have been optimized. The calculated static geometries (cell parameters, internal coordinates of atoms and bond lengths), bulk moduli and their pressure derivatives are in good agreement with the experimental data available. Predictions are made for those cases where no experimental data have been reported. The data clearly indicate that the elastic properties of all silicate garnets are dominated by the compressibility of the dodecahedral site. The compression mechanism is found to be based on a bending of the angle between the centers of the SiO4 tetrahedra and the adjacent octahedra, as in the aluminosilicate garnets. An analysis of the relationship between ionic radii of the cations and the compressibility of silicate garnets is presented.

A DFT Analysis of the Molecular Structures and Vibrational Spectra of Diphenylsulfone and 4,4'-Sulfonyldianiline (Dapsone)

2011 ◽  
Vol 66 (1) ◽  
pp. 69-76 ◽  
Author(s):  
Wolfgang Förner ◽  
Hassan M. Badawi
Keyword(s):  
Vibrational Spectra ◽  
Density Functional ◽  
Parent Compound ◽  
Harmonic Approximation ◽  
Molecular Structures ◽  
Spectral Lines ◽  
Basis Set ◽  
Minor Role ◽  
Parent Molecule ◽  
Chemical Difference

We have performed density functional calculations with the B3LYP functional and a 6-311G** basis set to obtain the vibrational spectra in harmonic approximation of the anti-leprosy drug Dapsone and the parent compound diphenylsulfone. Although the chemical difference between the two molecules is not that pronounced (Dapsone has amino groups in the para positions in the phenyl rings), Dapsone is an active drug, while to our knowledge diphenylsulfone shows no medical activity. We compared the theoretical results to experimental vibrational spectra found in the literature. With the help of the program GAUSSVIEW we were able to assign the experimentally found spectral lines to specific atomic motions. The remarkable difference between the two molecules, regarding their structural behavior, is that the drug Dapsone has a more flexible structure of the phenyl ring than the parent molecule has. This might contribute to a greater ability of the drug to fit into receptor sites in a cell membrane although one has to be well aware that this plays most propably only a minor role in the drug activity of Dapsone

Non-Linear Optical Properties and Global Reactivity Descriptors by ab initio Hartree-Fock (H.F.) Calculations of Simple Coumarins

2021 ◽  
Vol 9 (2) ◽  
pp. 7-20
Author(s):  
P. Sumalatha ◽  
◽  
N. Muralikrishna ◽  
K.V. Padmavathi ◽  
M. Subbarao ◽  
...  
Keyword(s):  
Optical Properties ◽  
Chemical Potential ◽  
Molecular Descriptors ◽  
Resistance To Change ◽  
Energy Difference ◽  
Polarizable Continuum Model ◽  
Basis Set ◽  
Optical Parameters ◽  
Reactivity Descriptors ◽  
Molecular Hyperpolarizability

In this present analysis, the measurement of optimized molecular structure and molecular hyperpolarizability (βtotal) of simple coumarin molecules were investigated using the HF method at 6-311G basis set level Gaussian09W. The measured nonlinear optical parameters (NLO); polarizability (α), the anisotropy of the polarizability (Δα), and first-order molecular hyperpolarizability (βtotal) of the studied coumarins indicate promising optical properties. The energy difference between HOMO and LUMO helped determine the molecular descriptors; global hardness (η), softness (σ) electronegativity (χ) Chemical potential (μ), and electrophilicity index (ω) in gas and different solvents. The molecular hyperpolarizability (βtotal) and descriptors that have been calculated in the solvent medium were taken into consideration through the Polarizable Continuum Model (PCM), This study shows the high static hyperpolarizability exhibited by HNR, FXT, and CNT and offers the potential the materials may have for NLO devices. The molecular descriptors, hardness, and chemical potential values are high for CNT and UCAcompared to other studied coumarins. This suggested that CNT and CA have the most significant chemical potential resistance to change the number of electrons among the other molecules.

Complete basis set, hybrid-density functional theory study, and natural bond orbital interpretations of the conformational behavior of halocarbonyl, thiocarbonyl, and selenocarbonyl isocyanates

2012 ◽  
Vol 90 (4) ◽  
pp. 333-343 ◽  
Author(s):  
Seiedeh Negar Mousavi ◽  
Davood Nori-Shargh ◽  
Hooriye Yahyaei ◽  
Kobra Mazrae Frahani
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Difference ◽  
Basis Set ◽  
Hybrid Density Functional Theory ◽  
Total Dipole Moment ◽  
Functional Theory ◽  
Complete Basis Set ◽  
Conformation Stability ◽  
Hybrid Density Functional

Complete basis set CBS-QB3, hybrid-density functional theory (B3LYP/Def2-TZVPP) based methods and NBO interpretation were used to investigate the impacts of the stereoelectronic effects and electrostatic and steric interactions on the conformational properties of halocarbonyl isocyanates (halo = F (1), Cl (2), and Br (3)), halothiocarbonyl isocyanates (halo = F (4), Cl (5), and Br (6)), and haloselenocarbonyl isocyanates(halo = F (7), Cl (8), and Br (9)). Both methods showed that the Z-conformations of compounds 1, 4, and 7 are more stable than their corresponding E conformations, but the stability of the E conformations, when compared with the corresponding Z conformations, increases from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9. The NBO analysis showed that the generalized anomeric effect (GAE) is in favor of the Z conformations of compounds 1, 4, and 7. The GAE values calculated (i.e., GAEE–GAEZ) increase from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9. On the other hand, there are none of the same trends between the calculated total dipole moment and the Gibbs free energy difference values between the E and Z conformations (i.e., ΔμE–Z and ΔGE–Z) of compounds 1–3, 4–6, and 7–9. Accordingly, the GAE succeeds in accounting for the increase of the E conformation stability from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9. Therefore, the GAE associated with the electron delocalization, not the total dipole moment changes (i.e., ΔμE–Z), is a reasonable indicator of the total energy difference in compounds 1–3, 4–6, and 7–9. There is a direct correlation between the calculated GAE and Δ[r2–6(E) – r2–6(Z)] parameters. Importantly, there are interesting through-space electron delocalizations (LP2X6→π*C4–O5) that justify the increase of the E conformation stability from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9, when compared with their corresponding Z conformations. The correlations between the GAE, bond orders, total steric exchange energies (TSEE), ΔGZ–E, ΔμE–Z, structural parameters, and conformational behaviors of compounds 1–9 were investigated.

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