Theoretical modeling and experimental studies on N-n-Decyl-2-oxo-5-nitro-1-benzylidene-methylamine

The Schiff base compound, N-n-Decyl-2-oxo-5-nitro-1-benzylidene-methylamine, has been -synthesized and characterized by IR, electronic spectroscopy, and X-ray single-crystal determination. Molecular geometry from X-ray experiment of the title compound in the ground state have been compared using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. Calculated results show that density functional theory (DFT) at B3LYP/6-31G(d) level can well reproduce the structure of the title compound. To investigate the solvent effect for the atomic charge distributions of the title compound, self-consistent reaction field theory with Onsager reaction field model was used. In addition, DFT calculations of the title compound, molecular electrostatic potential and thermodynamic properties were performed at B3LYP/6-31G(d) level of theory.     

Molecular structure and vibrational and chemical shift assignments of 5-(2-Hydroxyphenyl)-4-(p-tolyl)-2,4-dihydro-1,2,4-triazole-3-thione by DFT and <Emphasis Type="Italic">ab initio</Emphasis> HF calculations

The molecular geometry, vibrational frequencies, gauge including atomic orbital (GIAO) ¹H and ¹³C chemical shift values and several thermodynamic parameters of 5-(2-Hydroxyphenyl)-4-(p-tolyl)-2,4-dihydro-1,2,4-triazole-3-thione in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (DFT/B3LYP) with 6–31G(d), 6–31 + G(d,p) and LANL2DZ basis sets. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The computed vibrational frequencies are used to determine the types of molecular motions associated with each of the experimental bands observed. Also, calculated ¹H chemical shift values compared with the experimental ones. The data of the title compound display significant molecular structure and IR, NMR analysis provide the basis for future design of efficient materials having the of 1,2,4-triazole core.     

Density functional computational studies on (E)-2-[(2-Hydroxy-5-nitrophenyl)-iminiomethyl]-4-nitrophenolate

Density functional calculations of the structure, atomic charges, molecular electrostatic potential and thermodynamic functions have been performed at B3LYP/6-31G(d,p) level of theory for the title compound (E)-2-[(2-hydroxy-5-nitrophenyl)-iminiomethyl]-4-nitrophenolate. The results show that the phenolate oxygen atom and all of the nitro group oxygen atoms have bigger negative charges, and the coordination ability of these atoms differs in different solvents. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6-31G(d,p) basis set by applying the Onsager method and the isodensity polarized continuum model (IPCM). The results obtained with these methods reveal that the IPCM method yielded a more stable structure than Onsager’s method. In addition, natural bond orbital and frontier molecular orbital analysis of the title compound were performed using the B3LYP/6-31G(d,p) method.     

Excited state intramolecular proton transfer in 3-hydroxy flavone and 5-hydroxy flavone: A DFT based comparative study

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 3-hydroxy-flavone (3HF) and 5-hydroxy-flavone (5HF) were studied using DFT/B3LYP (6-31G (d,p)) and TD-DFT/B3LYP (6-31G (d,p)) level of theory respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Calculated PE curves of 3HF for the ground and excited singlet states proton transfer process explain its four state laser diagram. Excited states PE calculations support the ESIPT process to both 5HF and 3HF. The difference in ESIPT emission process of 3HF and 5HF have been explained in terms of HOMO and LUMO electron distribution of the enol and keto tautomer of these two compounds.     

Vibrational spectral assignments of paraldehyde by ab initio and density functional methods

The FTIR and Laser-Raman spectra of paraldehyde have been recorded in the regions 4000–400 cm⁻¹ and 3500–250 cm⁻¹ respectively. Molecular electronic energy, geometrical structure, harmonic vibrational spectra, infrared intensities and Raman scattering activities have been computed at the HF/6-31G(d,p) and B3LYP/6-31G(d,p) levels of theory. The results were compared with experimental values with the help of scaling procedures. The observed wave numbers in FTIR and Laser-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wave numbers in the expected range and are in good agreement with computed values.     

Electronic structure modeling of dinuclear copper(II)-methacrylic acid complex by density functional theory

A dinuclear centrosymmetric copper(II) complex with the formula [Cu₂(μ-maa)₄(maaH)₂] has been synthesized and experimentally characterized by IR, electronic spectroscopy, and X-ray single-crystal diffractometry. Starting from experimental X-ray geometry and using antiferromagnetic singlet ground state, gas phase geometry optimization was performed by density functional hybrid (B3LYP) method with 6-31G(d) and LANL2DZ basis sets. Gas-phase vibrational frequencies and single point energy (SPE) calculations have been carried out at the geometry-optimized structure. Molecular electrostatic potential calculated at the optimized geometry and natural bond orbital analysis data have been extracted from SPE output. The gas-phase electronic transitions of the title complex were investigated by the time dependent-density functional theory (TD-DFT) approach with the same theory employing LANL2DZ basis set. Also the calculated UV-Vis based upon TD-DFT results and IR spectra were simulated for comparison with the experimental ones.     

Experimental and theoretical investigation of the molecular and electronic structure of 5-(4-aminophenyl)-4-(3-methyl-3-phenylcyclobutyl)thiazol-2-amine

The title molecule, 5-(4-aminophenyl)-4-(3-methyl-3-phenylcyclobutyl)thiazol-2-amine (C₂₀H₂₁N₃S), was prepared and characterized by ¹H-NMR, ¹³C-NMR, IR and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/c with a?=?9.4350(5) Å, b?=?11.2796(6) Å, c?=?18.4170(8) Å and β?=?113.378(3)°. In addition to the molecular geometry from X-ray experiment, the molecular geometry, vibrational frequencies, gauge including atomic orbital (GIAO) ¹H- and ¹³C-NMR chemical shift values and atomic charges distribution of the title compound in the ground state have been calculated using the Hartree–Fock (HF) and density functional method (DFT) (B3LYP) with 6-31G(d) basis set. To determine conformational flexibility, molecular energy profile of the title compound was obtained by semi-empirical (AM1) calculations with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 10°. Besides, frontier molecular orbitals (FMO) analysis was performed by the B3LYP/6-31G(d) method.     

Ab initio and DFT study on the electrophilic addition reaction of bromine to tetracyclo[5.3.0.02,6.03,10]deca–4,8–diene

The electronic and geometric structures of tetracyclo[5.3.0.0^2,6.0^3,10]deca-4,8-diene (hypostrophene) have been investigated by ab initio and DFT/B3LYP methods using the 6-31G* and 6-311G* basis sets. The double bonds of hypostrophene are endo-pyramidalized. The cationic intermediates and products formed in the addition reaction have been investigated using the HF/6-311G*, HF/6-311G**, and B3LYP/6-311G* methods. The bridged bromonium cation was more stable than the U-type cation. Considering that the bridged cation does not isomerize to the less stable U-type cation, it is not possible for the U-type product to be obtained in the reaction. The bridged bromonium cation transformed into the more stable N-type cation and the N-type product was obtained via this cation. The thermodynamic stability of the exo, exo and exo, endo isomers of the N-type dibromide molecule were almost identical. The N-type product was 16.6 kcal mol⁻¹ more stable than the U-type product. Figure General energy diagram of the hypostrophene–bromine (HS–Br₂) system (kcal mol⁻¹) (MP2/6-311G*//HF/6-311G*)     

An experimental and theoretical approach to the molecular structure of 2-{4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]thiazol-2-yl}isoindoline-1,3-dione

The title compound, 2-{4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]thiazol-2-yl}isoindoline-1,3-dione (C₂₄H₂₂N₂O₂S), was synthesized and characterized by IR-NMR spectroscopy and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/c with a?=?19.7799(13) Å, b?=?6.7473(4) Å, c?=?15.7259(9) Å and β?=?103.416(5)°. In addition, the molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) ¹H and ¹³C chemical shift values of the title compound in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (DFT/B3LYP) with 6–31G(d), 6–31 + G(d,p) and LANL2DZ basis sets, and compared with the experimental data. To determine conformational flexibility, molecular energy profile of the title compound was obtained by semi-empirical (AM1) calculations with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 5°. Besides, molecular electrostatic potential, frontier molecular orbitals (FMO) analysis and thermodynamic properties of the title compound were investigated by theoretical calculations.     

Methyl 2-methoxy-7-(4-methylbenzoyl)-4-oxo-6-p-tolyl-4H-furo[3,2-c]pyran-3-carboxylate:A combined experimental and theoretical investigation

The title compound, methyl 2-methoxy-7-(4-methylbenzoyl)-4-oxo-6-p-tolyl-4H-furo[3,2-c]pyran-3-carboxylate (C₂₅H₂₀O₇), was prepared and characterized by IR and single-crystal X-ray diffraction (XRD). The compound crystallizes in the triclinic space group P ?1 with a?=?8.9554(9) Å, b?=?10.0018(10) Å, c?=?12.7454(13) Å, α?=?67.678(7)°, β?=?89.359(8)° and γ?=?88.961(8)°. In addition to the molecular geometry from X-ray experiment, the molecular geometry and vibrational frequencies of the title compound in the ground state have been calculated using semiempirical AM1 and PM3 methods, as well as Hartree-Fock (HF) and density functional (B3LYP) levels of theory with 6–31G(d) basis set. To determine conformational flexibility, molecular energy profile of the title compound was obtained by semi-empirical (AM1) calculations with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 10°. Besides, frontier molecular orbitals (FMO) analysis and thermodynamic properties of the title compound were performed by the B3LYP/6–31G(d) method.     

Molecular modeling of 4-methylphthalonitrile for dye sensitized solar cells using quantum chemical calculations

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 4-Methylphthalonitrile was studied based on Hartree-Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-Vis) spectrum was investigated by time dependent-density functional theory (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to π → π* transitions. Calculated results suggest that three lowest energy excited states of 4-Methylphthalonitrile are due to photo induced electron transfer processes. The interfacial electron transfer between semiconductor TiO₂ electrode and dye sensitizer 4-Methylphthalonitrile is due to an electron injection process from excited dye to the semiconductor’s conduction band. The role of cyanine and methyl group in 4-Methylphthalonitrile in geometries, electronic structures, and spectral properties were analyzed.     

Theoretical study on the thermal decomposition of model compounds for Poly (dialkyl fumarate)

The thermal decomposition of model compounds for poly (dialkyl fumarate) was studied by using ab initio and density functional theory (DFT) calculations. To determine the most favorable reaction pathway of thermal decomposition, geometries, structures, and energies were evaluated for reactants, products, and transition states of the proposed pathways at the HF/6-31G(d) and B3LYP/6-31G(d) levels. Three possible paths (I, II and III) and subsequent reaction paths (IV and V) for the model compounds of poly (dialkyl fumarate) decomposition had been postulated. It has been found that the path (I) has the lowest activation energy 193.8 kJ mol⁻¹ at B3LYP/6-31G(d) level and the path (I) is considered as the main path for the thermal decomposition of model compounds for poly (dialkyl fumarate).      

Electronic structure simulations of 2,6-dimethyl-2,5-heptadien-4-one by FTIR,FT-Raman,NMR, UV–vis,NBO and density functional theory

Density functional theory (DFT) (B3LYP and B3PW91) calculations have been carried out for 2,6-dimethyl-2,5-heptadien-4-one (DMHD4O) using 6–311++ G** basis set. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out from the FTIR and FT-Raman spectral data. The theoretical electronic absorption has been calculated by using time-dependent DFT (TD-DFT) methods and compared with the experimental spectra. The theoretically computed Frontier energy gaps and TD-DFT calculations are in good agreement with the experimental UV–vis spectral absorption. The chemical hardness measured from the Frontier molecular orbital energies of DMHD4O is 0.0693 eV. Electronic stability of the compound arising from hyperconjugative interactions and charge delocalisation were also investigated based on the natural bond orbital (NBO) analysis. Effective stabilisation energy E ⁽²⁾ associated with the interactions of the π and the lone pair of electrons was determined by the NBO analysis. ¹³C and ¹H NMR chemical shifts of the compound have been calculated by means of Gauge-Invariant Atomic Orbital using B3LYP/6–311++ G** method. The partial ionic character of the carbonyl group due to resonance render a partially positive charge to the carbonyl carbon, and thus C4 chemical shift lie in the very downfield 191.6 ppm. Comparison between the experimental and the theoretical results indicates that B3LYP method is able to provide satisfactory results for predicting vibrational, electronic and NMR properties.     

Spectroscopic (FTIR,FT-Raman,NMR and UV) and molecular structure investigations of 1,5-diphenylpenta-2,4-dien-1-one: a combined experimental and theoretical approach

The title molecule 1,5-diphenylpenta-2,4-dien-1-one (cinnamylideneacetophenone, CA) has been synthesised and characterised by FTIR, FT-Raman, NMR and UV–vis spectral analyses. The possible stable conformers of the CA molecule were searched by potential energy surface scan at B3LYP level of theory. The molecular geometry from X-ray determination of the CA molecule in the ground state has been compared using the density functional theory (DFT) with 6-31G(d,p) basis set. The harmonic vibrational modes, the corresponding wavenumbers and IR and Raman intensities of most stable conformer were calculated by the DFT method. The assignments of the fundamentals were proposed on the basis of total energy distribution calculations. The calculated ¹³C and ¹H NMR chemical shifts using gauge including atomic orbitals approach are in good agreement with the observed chemical shifts. The molecular stability and bond strength have been investigated by applying natural bond orbital analysis. Using the time-dependent DFT method, the electronic absorption spectrum of the title compound has been predicted and the electronic transitions within the molecule have been interpreted. The molecular electrostatic potential map was used for predicting possible hydrogen and oxygen bonding sites in the CA molecule.     

Experimental and DFT computational studies on 5-benzyl-4-(3,4-dimethoxyphenethyl)-2H-1,2,4-triazol-3(4H)-one

The triazole compound, 5-benzyl-4-(3,4-dimethoxyphenethyl)-2H-1,2,4-triazol-3(4H)-one, has been synthesized and characterized by ¹H-NMR, ¹³C-NMR, IR, and X-ray single-crystal determination. The compound crystallizes in the monoclinic space group P2₁ with a?=?11.8844(3) Å, b?=?17.5087(4) Å, c?=?17.3648(6) Å, β?=?99.990(2)? and Z?=?8. In addition to the molecular geometry from X-ray experiment, the molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) ¹H- and ¹³C-NMR chemical shift values of the title compound in the ground state have been calculated using the density functional method (B3LYP) with 6-31G(d,p) basis set. The calculated results show that the optimized geometries can well reproduce the crystal structure and the theoretical vibrational frequencies and chemical shift values show good agreement with experimental ones. Besides, molecular electrostatic potential (MEP), natural bond orbital (NBO), and frontier molecular orbitals (FMO) analysis of the title compound were performed by the B3LYP/6-31G(d,p) method.     

Ab initio study of phenyl benzoate: structure,conformational analysis,dipole moment,IR and Raman vibrational spectra

The molecular structure (bond distances and angles), conformational properties, dipole moment and vibrational spectroscopic data (vibrational frequencies, IR and Raman intensities) of phenyl benzoate were calculated using Hartree–Fock (HF), density functional (DFT), and second order Møller–Plesset perturbation theory (MP2) with basis sets ranging from 6-31G* to 6-311++G**. The theoretical results are discussed mainly in terms of comparisons with available experimental data. For geometric data, good agreement between theory and experiment is obtained for the MP2, B3LYP and B3PW91 levels with basis sets including diffuse functions. The B3LYP/6-31+G* theory level estimates the shape of the experimental functions for phenyl torsion around the Ph–O and Ph–C bonds well, but reproduces the height of the rotational barriers poorly. The B3LYP/6-31+G* harmonic force constants were scaled by applying the scaled quantum mechanical force field (SQM) technique. The calculated vibrational spectra were interpreted and band assignments were reported. They are in excellent agreement with experimental IR and Raman spectra.Figure Calculated and experimental (GED) potential energy functions for torsional motion of phenyl benzoate relative to the minimum value. a The potential function for torsion about the O₃–C₄ bond. b The potential function for torsion about the C₂–C₁₀ bond.     

Electronic structure study using density functional theory in organic dendrimers

The electronic and structural properties of pyrrolic ring derivatives were studied using density functional theory (DFT) in terms of their application as organic semiconductor materials in photovoltaic devices. The B3LYP hybrid functional in combination with Pople type 6-31G(d) basis set with a polarization function was used in order to determine the optimized geometries and the electronic properties of the ground state, while transition energies and excited state properties were obtained from time-dependent (TD)-DFT with B3LYP/6-31G(d) calculation. The investigation of pyrrolic derivatives formed by the arrangement of several monomeric units revealed that three-dimensional (3D) conjugated architectures in which the combination of a triphenylamine (TPA) core with π-conjugated rings attached to the core, present the best geometric and electronic characteristics for use as an organic semiconductor material. The highest occupied molecular orbital (HOMO) − lowest unoccupied molecular orbital (LUMO) energy gap was decreased in 3D-structures that extend the absorption spectrum toward longer wavelengths, revealing a feasible intramolecular charge transfer process in these systems. All calculations in this work were performed using the Gaussian 03 W software package.     

Theoretical 49Ti NMR chemical shifts

⁴⁹Ti chemical shifts for a total of 20 titanium complexes are reported, and several levels of theory are evaluated in order to identify a reliable approach for the calculation of titanium NMR data. The popular B3LYP/6–31G(d)//B3LYP/6–31G(d) proves to give very good agreement with experimental data over a range from 1,400 to −1,300 ppm. The MP2/6–31G(d)//MP2/6–31G(d) level computes even smaller average deviations but fails for TiI₄. This behavior together with its huge demand for computational resources requires careful handling of this theoretical level. In addition, NMR data for five titanium fulvene (or related) complexes are given. Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday     

Comparative theoretical study of the UV/Vis absorption spectra of styrylpyridine compounds using TD-DFT calculations

This study examined absorption properties of 2-styrylpyridine, trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)]pyridine, and trans-4-(m-cyanostyryl)pyridine compounds based on theoretical UV/Vis spectra, with comparisons between time-dependent density functional theory (TD-DFT) using B3LYP, PBE0, and LC-ωPBE functionals. Basis sets 6–31G(d), 6–31G(d,p), 6–31+G(d,p), and 6–311+G(d,p) were tested to compare molecular orbital energy values, gap energies, and maxima absorption wavelengths. UV/Vis spectra were calculated from fully optimized geometry in B3LYP/6–311+G(d,p) in gas phase and using the IEFPCM model. B3LYP/6–311+G(d,p) provided the most stable form, a planar structure with parameters close to 2-styrylpyridine X-ray data. Isomeric structures were evaluated by full geometry optimization using the same theory level. Similar energetic values were found: ～4.5 kJ?mol^?1 for 2-styrylpyridine and ～1 kJ?mol^?1 for derivative compound isomers. The 2-styrylpyridine isomeric structure differed at the pyridine group N-atom position; structures considered for the other compounds had the cyano group attached to the phenyl ring m-position equivalent. The energy difference was almost negligible between m-cyano-substituted molecules, but high energy barriers existed for cyano-substituted phenyl ring torsion. TD-DFT appeared to be robust and accurate approach. The B3LYP functional with the 6–31G(d) basis set produced the most reliable λ_max values, with mean errors of 0.5 and 12 nm respect to experimental values, in gas and solution, respectively. The present data describes effects on the λ_max changes in the UV/Vis absorption spectra of the electron acceptor cyano substituent on the phenyl ring, the electron donor methyl substituent, and the N-atom position on the electron acceptor pyridine ring, causing slight changes respect to the 2-styrylpyridine title compound.     

Structure and electronic absorption spectra of nematogenic alkoxycinnamic acids - a comparative study based on semiempirical and DFT methods

Structure of nematogenic p-n-Alkoxy cinnamic acids (nOCAC) with various alkyl chain carbon atoms (n = 2, 4, 6, 8) has been optimized using density functional B3LYP with 6-31+G (d) basis set using crystallographic geometry as input. Using the optimized geometry, electronic structure of the molecules has been evaluated using the semiempirical methods and DFT calculations. Molecular charge distribution and phase stability of these systems have been analyzed based on Mulliken and L?wdin population analysis. The electronic absorption spectra of nOCAC molecules have been simulated by employing DFT method, semiempirical CNDO/S and INDO/S parameterizations. Two types of calculations have been performed for model systems containing single and double molecules of nOCAC. UV-Visible spectra have been calculated for all single molecules. The UV stability of the molecules has been discussed in light of the electronic transition oscillator strength (f). The dimer complexes of higher homologues (n = 6, 8) have also been reported to enable the comparison between single and double molecules.