Molecular structure,spectroscopic properties (FT-IR,Micro-Raman,and UV-vis), and DFT calculations of minaprine

Molecular geometry, experimental vibrational wavenumbers, electronic properties, and quantum chemical calculations of minaprine (C₁₇H₂₂N₄O · 2HCl), (with synonym, dihydrochloride salt of N-(4-methyl-6-phenyl-3-pyridazinyl)-4-morpholineethamine) which is widely used as a psychotropic drug at medicinal treatment, in the ground state by using density functional theory (DFT/B3LYP) method with 6–31++G(d,p) basis set have been presented for the first time. The comparison of the observed fundamental vibrational frequencies were in a very good agreement with the experimental data. Furthermore, UV-vis TD-DFT calculations, the highest occupied molecular orbitals (HOMO-1, HOMO), lowest unoccupied molecular orbitals (LUMO, LUMO + 1), molecular electrostatic potential (MEP) surface, atomic charges and thermodynamic properties of minaprine molecule have been theoretically calculated and simulated at the mentioned level.     

The molecular structures, vibrational spectroscopies (FT-IR and Raman) and quantum chemical calculations of n-alkyltrimethylammonium bromides

The FT-IR and micro-Raman spectra of three n-alkyltrimethylammonium bromides (dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and hexadecyl(cetyl)trimethylammonium bromide (CTAB)) in powder form were recorded in the regions 4000–550 cm^?1 and 3200–300 cm^?1, respectively. The optimized geometries and vibrational frequencies of DTAB, TTAB and CTAB have been carried out with ab initio Hartree-Fock (HF) and density functional theory method B3LYP calculations with the 6–31 G (d, p) basis set in the ground state. The comparison of the observed fundamental vibrational frequencies and calculated results for the fundamental vibrational frequencies of DTAB, TTAB and CTAB indicate that the scaled B3LYP method is superior compared to the scaled HF method.     

FT‐Raman and FT‐IR spectral and quantum chemical studies on some flavonoid derivatives: Baicalein and Naringenin

In this study, the experimental and theoretical results on the molecular structures of some flavonoid derivatives (Baicalein and Naringenin) are presented. The FT‐IR and FT‐Raman spectra of the compounds have been recorded together for the first time between 4000–400 cm⁻¹ and 3500–5 cm⁻¹ regions, respectively. The molecular geometry and vibrational wavenumbers of the compounds have been also calculated in their ground states by using ab initio HF and DFT/B3LYP functional with 6‐31G(d,p) basis set used in calculations. The calculations were utilized to the C₁ symmetries of the molecules. All calculations were performed with Gaussian 98 software. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Scale factors have been used in order to compare how the calculated and experimental data are in agreement. Theoretical infrared intensities were also reported. Copyright © 2008 John Wiley & Sons, Ltd.     

FT‐Raman,FT‐IR spectral and DFT studies on 6, 8‐dichloroflavone and 6, 8‐dibromoflavone

In this study, experimental and theoretical vibrational spectral results of the molecular structures of 6,8‐dichloroflavone (6,8‐dcf) and 6,8‐dibromoflavone (6,8‐dbf) are presented. The FT‐IR and FT‐Raman spectra of the compounds have been recorded together between 4000 and 400 cm⁻¹ and 3500–5 cm⁻¹ regions, respectively. The molecular geometry and vibrational wavenumbers of 6,8‐dcf and 6,8‐dbf in their ground state have been calculated by using DFT/B3LYP functional, with 6‐31 + + G(d,p) basis set used in calculations. All calculations were performed with Gaussian03 software. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Scale factors have been used in order to compare how the calculated and experimental data are in agreement. Theoretical infrared intensities are also reported. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural,Spectroscopic, Antimicrobial Activity and DFT Studies on 4-Methyl-<Emphasis Type="Italic">N</Emphasis>-(4-methylphenylsulfonyl)-<Emphasis Type="Italic">N</Emphasis>-phenylbenzenesulfonamide

This study reports the structural characterization of a disulfonimide derivative, 4-methyl-N-(4-methylphenylsulfonyl)-N-phenylbenzenesulfonamide (MPBSA), using spectroscopic and quantum chemical methods. The molecule was characterized with FT-IR, ¹H ¹³C NMR and UV-Vis spectroscopies. Quantum chemical calculations of molecular geometry, vibrational wavenumbers and gauge including atomic orbital (GIAO) ¹H and ¹³C-NMR chemical shifts of the compound were carried out by using density functional method (DFT) at B3LYP/6?311++G(d,p) level of theory. Electronic absorption spectra of the compound have been computed using the time-dependent density functional theory (TD-DFT) method at the same level. A satisfactory consistency between the experimental and theoretical findings was obtained. The antimicrobial activity screening of the compound was performed on some bacteria and fungus species using microdilution method. The results showed that the title molecule have noteworthy antibacterial and antifungal activities.     

Molecular structure, spectroscopic properties and DFT calculations of 2-(methylthio)nicotinic acid

The analyses of possible conformations, molecular structures, vibrational and electronic properties of 2-(methylthio)nicotinic acid molecule, C₇H₇NO₂S, with the synonym 2-(methylsulfanyl)nicotinic acid have been first presented theoretically. At the same time, FT-IR and micro-Raman spectra of 2-(methylthio)nicotinic acid were recorded in the regions 400–4000 cm^?1 and 100–4000 cm^?1, respectively. In our calculations, the DFTB3LYP method with 6–311G(d, p) basis set was used to have the structural and spectroscopic data about the mentioned molecule in the ground state and the results obtained were compared with experimental values. Furthermore, gauge invariant atomic orbital (GIAO) ¹H and ¹³C NMR chemical shifts in different solvents, UV-vis TD-DFT calculations, the highest occupied molecular orbitals (HOMO-2, HOMO-1, HOMO), lowest unoccupied molecular orbital (LUMO), molecular electrostatic potantial (MEP) surface, atomic charges and thermodynamic properties of molecule have been theoretically verified and simulated at the mentioned level. The energetic behavior of title molecule in different solvent media was investigated by using DFT/B3LYP method with 6–311G(d, p) basis set in terms of integral equation formalism polarizable continuum model (IEFPCM). In addition, the calculated infrared intensities, Raman activities, reduce masses and force constants of the compound under study have been also reported.     

DFT and TD-DFT study on structure and properties of organic dye sensitizer TA-St-CA

The geometry, electronic structure, polarizability and hyperpolarizability of organic dye sensitizer TA-St-CA, which contains a π-conjugated oligo-phenylenevinylene unit with an electron donor–acceptor moiety, was studied using density functional theory (DFT), and the electronic absorption spectrum was investigated via time-dependent DFT (TD-DFT) with several hybrid functionals. The calculated geometry indicates that the strong conjugated effects are formed in the dye. The TD-DFT results show that the hybrid functional PBE1PBE and MPW1PW91 are more suitable than B3LYP for calculating electronic absorption spectra. The features of electronic absorption spectra were assigned on account of the qualitative agreement between the experiment and the calculations. The absorption bands in visible and near-UV region are related to photoinduced electron transfer processes, and the diphenylaniline group is major chromophore that contributed to the sensitization, and the interfacial electron transfer are electron injection processes from the excited dyes to the semiconductor conduction band. Compared with the similar dye D5, the good performance of TA-St-CA in dye-sensitized solar cells may be resulted from the higher energy level of the lowest unoccupied molecular orbital and the larger oscillator strengths for the most excited states with intramolecular electron transfer character.     

Spectroscopic analysis,AIM, NLO and VCD investigations of acetaldehyde thiosemicarbazone using quantum mechanical simulations

The prepared Acetaldehyde thiosemicarbazone (ATSC) have been investigated by both the experimental and theoretical methods; through this work, the essentiality of elucidation of molecular fragments source linear and non-linear optical properties was explored. The stability of the structure and entire calculations have been performed on HF and B3LYP methods with 6-311++G(d,p) level of basis set. The Mulliken charge profile, electronic, optical and hyper polarizability analyses have been carried out in order to evaluate nonlinear optical (NLO) performance of the present compound. The exact optical location of the ATSC was determined by executing UV–Visible calculations on TDSCF method. The existence of the molecular group for the inducement and tuning of NLO properties were thoroughly investigated by performing fundamental vibrational investigation. The optical energy transformation among frontier molecular levels has been described in UV–Visible region. The Gibbs energy coefficient of thermodynamic functions was monitored in different temperature and it was found constant irrespective of temperatures. The appearance of different chemical environment of H and C was monitored from the ¹H and ¹³C NMR spectra. The vibrational optical polarization characteristics with respect to molecular composition in the compound have been studied by VCD spectrum. The bond critical point, Laplacian of electron density, electron kinetic energy density and total electron energy density have calculated and analysed using AIM study.     

Computational Studies on the Ground State Tautomer,Hydrogen Conformations and Vibrational Spectroscopic Analysis of Antitumor Agents:3-Deazauracil and 6-Azauracil

The ground state hydrogen conformations and vibrational analysis of 3-deazauracil (3DAU) and 6-azauracil (6AU) tautomers (4-enol and 2,4-diol forms) have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d,p) basis set level. The calculations have shown that the most probably preferential tautomer of 3DAU and 6AU are the 4-enol form, which gives best fit to the corresponding experimental data. The ground state conformer of the 2,4-diol form has two O-H bonds which are oriented externally and internally (to the N-H bond). The vibrational analyses of the ground state conformer of each tautomeric form of 3DAU and 6AU were done and their optimized geometry parameters (bond lengths and bond angles) were given. Furthermore, from the correlations values it was concluded that the B3LYP method is superior to the HF method for both the vibrational frequencies and the geometric parameters.     

A combined experimental and computational studies of 3,3,6,6-Tetramethyl-9-(4-Methoxyphenyl)3,4,6,7,9,10 hexahydroacridine-1,8-dione

ABSTRACT

In this work, we have recorded the Fourier Transform Infrared (FTIR) and Ultra-Violet Visible (UV–Vis) spectra of 3,3,6,6-Tetramethyl-9-(4-Methoxyphenyl)3,4,6,7,9,10 hexahydroacridine-1,8-dione (C₂₄H₂₉NO₃) in the spectral range 4000–400?cm^?1 and 190–1400?nm, respectively. The thermo gravimetric (TG) analysis of the compound has been performed to check the thermal stability of the compound. The molecular geometry and complete vibrational spectra in the ground state are calculated by Hartree Fock (HF) and Density Functional Theory (DFT) using6-311G(d,p) basis set. The calculated vibrational harmonic frequencies are scaled using a proper scale factor, yielding a good agreement with the experimental data. Stability of the molecule arising from hyperconjugative interactions, charge delocalisation has been studied using natural bond orbital analysis (NBO). Mulliken charges, MEP mapping and temperature dependence on the thermodynamic properties in the optimised ground state have been calculated. UV–Visible spectrum of the molecule was calculated by using TD-DFT approach and the results were compared with the experimental one. We have calculated the several molecular parameters like ionisation potential, electron affinity, global hardness, electron chemical potential, electronegativity and global electrophilicity based on HOMO and LUMO energy values calculated at B3LYP/6-311G(d,p) level of theory. The calculated optimised structural parameters and vibrational wavenumbers are found to be in good agreement with the experimental results.     

Scaled Quantum Chemical Studies of the Molecular Structure and Vibrational Spectra of Minoxidil

The Fourier transform Raman and Fourier transform infrared spectra for minoxidil have been recorded in the region 4000—100 cm^?1 and 4000—450 cm^?1, respectively. The structural and spectroscopy data of the molecule in the ground state were calculated by using density functional theory methods with 6-311G (d, p) basis set. A detailed vibrational analysis of the title compound has been done using normal coordinate analysis following the scaled quantum mechanical force field methodology. The calculated molecular geometry parameters and scaled vibrational wavenumbers are well compared with the experimental data. The electronic properties, such as excitation energies, absorption wavelength, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) energies were performed by time-dependent density functional theory approach, and the results are in good agreement with experimental absorption spectrum. The charge delocalizations of these molecules have been analyzed using natural bond orbital analysis. The molecule orbital contributions are studied by density of energy states. Fukui functions, local softness, and electrophilicity indices for selected atomic sites of the title compound are determined. Finally, the thermal behaviors of the compound have been calculated by different temperature.     

Experimental (UV,NMR, IR and Raman) and theoretical spectroscopic properties of 2-chloro-6-methylaniline

In this work, the experimental and theoretical UV, NMR and vibrational spectra of 2-chloro-6-methylaniline (2-Cl-6-MA, C₇H₈NCl) were studied. The ultraviolet absorption spectra of compound that dissolved in ethanol were examined in the range of 200–400 nm. The ¹H, ¹³C and DEPT NMR spectra of the compound were recorded. FT-IR and FT-Raman spectra of 2-Cl-6-MA in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies were found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. Comparison of the calculated NMR chemical shifts and absorption wavelengths with the experimental values revealed that DFT method produces good results.     

Vibrational,NMR and UV–visible spectroscopic investigation and NLO studies on benzaldehyde thiosemicarbazone using computational calculations

In order to investigate the vibrational, electronic and NLO characteristics of the compound; benzaldehyde thiosemicarbazone (BTSC), the XRD, FT-IR, FT-Raman, NMR and UV–visible spectra were recorded and were analysed with the calculated spectra by using HF and B3LYP methods with 6-311++G(d,p) basis set. The XRD results revealed that the stabilized molecular systems were confined in orthorhombic unit cell system. The cause for the change of chemical and physical properties behind the compound has been discussed makes use of Mulliken charge levels and NBO in detail. The shift of molecular vibrational pattern by the fusing of ligand; thiosemicarbazone group with benzaldehyde has been keenly observed. The occurrence of in phase and out of phase molecular interaction over the frontier molecular orbitals was determined to evaluate the degeneracy of the electronic energy levels. The thermodynamical studies of the temperature region 100–1000 K to detect the thermal stabilization of the crystal phase of the compound were investigated. The NLO properties were evaluated by the determination of the polarizability and hyperpolarizability of the compound in crystal phase. The physical stabilization of the geometry of the compound has been explained by geometry deformation analysis.     

FTIR spectroscopic and quantum-chemical studies on some tribromoindenes and their isomers

Combined experimental and computational studies on molecular structure of newly synthesised transtirans 1,2,3-tribromo-1,2,3-trihydro-¹H-benz[f]indene (TTTBI) were reported. Also, only computational studies were done for cis-trans-1,2,3-tribromo-1,2,3-trihydro-¹H-benz[f]indene (CTTBI) and cis-cis-1,2,3-tribromo-1,2,3-trihydro-¹H-benz[f]indene (CCTBI) in order to understand the vibrational spectra and molecular parameters of them. The geometry optimization and vibrational wave numbers of the title molecules were carried out with the Gaussian98 program package by using Hartree-Fock (HF) and Density Functional Theory (DFT) with B3LYP functional and 6–31G (d) basis set. All calculations were done for the title compounds in their ground states. Especially for CTTBI and CCTBI, which could not be synthesized yet, these kind of pre-calculations take an important role for their synthesis process. Also crystal structural parameters of TTTBI by single-crystal X-ray diffraction method was used as input for computational study of it. Observed and calculated vibrational wave numbers were compared. Because the use of benz[f]indene as a cyclopentadienyl ligand attracted much attention because an annulated benzo ring might increase both the stereocontrol and productivity of catalytic system, TTTBI and other computationally studied and modeled two molecules may play an important role of other types of compounds as a starting structures.     

Conformational stability and vibrational study of phenylacetyl chloride

The Fourier transform infrared spectroscopy and Fourier transform Raman spectra of phenylacetyl chloride were recorded and analyzed in the range 3500–400 and 3500–200 cm^?1 at room temperature, respectively. In order to obtain the structural information and conformational stabilities, a potential energy surface scan for internal rotation was carried out at the B3LYP/6‐31G(d) level. The potential energy surface reveals that the title compound has two minimal conformers (A and B). The optimized geometries, structural parameters, stabilities, energies, thermodynamic parameters, vibrational wavenumbers, infrared intensities, and Raman activities for the two conformers (A and B) have been obtained by employing B3LYP and MP2 calculations with 6‐311++G (d, p) basis sets. The conformational energy difference between A and B is very small, indicating that the B conformer coexists with the A conformer. The detailed vibrational assignments of vibrational spectra of each conformer have been made on the basis of the potential energy distributions analysis. The highest occupied molecular orbital –lowest unoccupied molecular orbital energy gap and molecular electrostatic potential of the two conformers have been also calculated for comparison of their chemical activities. Copyright © 2015 John Wiley & Sons, Ltd.     

基于密度泛函理论的菲分子结构与光谱研究

选用密度泛函理论(DET)中的B3LYP方法,在6-311++G(d,p)下对菲分子结构进行优化,计算了其振动频率、极化率及热力学参数,对比了菲分子实测光谱图,首次对其振动频率进行了完全归属。此外,分析并讨论了其前线分子轨道、分子静电势和密立根布局,获得了HOMO-LUMO能隙、分子静电势分布、原子电荷分布等与分子性质密切相关的重要数据,为后续其他多环芳烃分子的光谱检测技术及其光谱和电子结构的分析提供了理论基础。     

Experimental vibrational spectra (Raman,infrared) and DFT calculations on monomeric and dimeric structures of 2‐ and 6‐bromonicotinic acid

In this work, the Fourier transform infrared and Raman spectra of 2‐bromonicotinic acid and 6‐bromonicotinic acid (abbreviated as 2‐BrNA and 6‐BrNA, C₆H₄BrNO₂) have been recorded in the region 4000–400 and 3500–50 cm⁻¹. The optimum molecular geometry, normal mode wavenumbers, infrared intensities and Raman scattering activities, corresponding vibrational assignments and intermolecular hydrogen bonds were investigated with the help of B3LYP density functional theory (DFT) method using 6‐311++G(d,p) basis set. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. Copyright © 2009 John Wiley & Sons, Ltd.     

The 4d, 5s,and 5p Orbitals of Rhodium

The 4d, 5s, and 5p orbitals of rhodium have been studied by semiempirical molecular orbital calculations for a Rh2 molecule. Overlap populations, overlap energy, and orbital energies were computed as functions of the orbital exponents of Slater type atomic orbitals. This study was prompted by extremely unsatisfactory results obtained attempting to predict electronic spectra, structure, and bonding in a number of rhodium complexes using analytic atomic orbitals deduced1 from accurate Hartree-Pock(HF) atomic calculations. “These reference calculations considered only the atomic configuration (4d)⁷(5s)² for rhodium.     

Quantum chemical calculations of bond dissociation energies for COOH scission and electronic structure in some acids

Quantum chemical calculations are performed to investigate the equilibrium C-COOH bond distances and the bond dissociation energies(BDEs) for 15 acids.These compounds are studied by utilizing the hybrid density functional theory(DFT)(B3LYP,B3PW91,B3P86,PBE1PBE) and the complete basis set(CBS-Q) method in conjunction with the 6311G** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work.Comparisons between the computational results and the experimental values reveal that CBS-Q method,which can produce reasonable BDEs for some systems in our previous work,seems unable to predict accurate BDEs here.However,the B3P86 calculated results accord very well with the experimental values,within an average absolute error of 2.3 kcal/mol.Thus,B3P86 method is suitable for computing the reliable BDEs of C-COOH bond for carboxylic acid compounds.In addition,the energy gaps between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of studied compounds are estimated,based on which the relative thermal stabilities of the studied acids are also discussed.     

Molecular structure,NMR and vibrational spectral analysis of 2,4‐difluorophenol by ab initio HF and density functional theory

Quantum chemical calculations of energies, geometries and vibrational wavenumbers of 2,4‐difluorophenol (2,4‐DFP) were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6‐311G(d,p) as basis set. The optimized geometrical parameters obtained by HF and DFT calculations are in good agreement with related molecules. The best level of theory in order to reproduce the experimental wavenumbers is the B3LYP method with the 6‐311G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of 2,4‐DFP is also reported. The entropy of the title compound was also performed at HF/6‐311G(d,p) and B3LYP/6‐311G(d,p) levels of theory. The isotropic chemical shift computed by ¹H, ¹³C NMR analyses also shows good agreement with experimental observations. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule have been constructed. Copyright © 2009 John Wiley & Sons, Ltd.