Experimental and theoretical FT-IR and FT-Raman spectroscopic analysis of N1-methyl-2-chloroaniline

1,3,4-oxadiazole derivatives: synthesis, characterization, antifungal activity, DNA binding investigations, TD-DFT calculations, and molecular modelling

1,3,4-Oxadiazole-based heterocyclic analogs (3a-3m) were synthesized via cyclization of Schiff bases with substituted aldehydes in the presence of bromine and acetic acid. The structural clarification of synthesized molecules was carried out with various spectroscopic techniques such as FT-IR,1H and 13C-NMR, UV-visible spectroscopy, and mass spectrometry. In-vitro antifungal activity was performed against C. albicans, C. glabrata and C. tropicalis and analogs 3g, 3i, and 3m showed potent MIC at 200 µg/ml and excellent ZOI measurements of 17-21 nm. The cell viability on Huh7 for lead molecules 3g, 3i, and 3m was found to be 99.5%, 92.3%, and 86.9% at 20, 10, and 20 μM, respectively. The antioxidant activity of molecules 3 g, 3i, and 3 m was estimated and exhibited great IC50 values of 0.104 ± 0.021, 0.145 ± 0.05, and 0.165 ± 0.018 μg/mL with DPPH and 0.107 ± 0.04, 0.191 ± 0.12, and 0.106 ± 0.08 with H2O2, respectively. The binding interaction mode for the lead molecules was also carried out with Ct-DNA using the absorption, emission, CV, CD, and Time resolve fluorescence techniques. The results showed good binding constant (Kb) values of 9.1 × 105, 9.94 × 105, and 9.32 × 105 M-1 for 3g, 3i, and 3m, respectively. TD-DFT study of compounds 3g, 3i, and 3m was done to find out HOMO/LUMO energy levels, surface study of the molecular electrostatic potential, Mulliken population analysis, and natural bond orbitals showing the linkages between the donors and acceptors.Molecular docking of three lead analogs with PDB ID: 1BNA and molecular modelling of compounds 3g, 3i, and 3m with C. albicans CYP51 protein (PDB ID: 5FSA) were carried out.Communicated by Ramaswamy H. Sarma.

Exploring quantum computational, molecular docking, and molecular dynamics simulation with MMGBSA studies of ethyl-2-amino-4-methyl thiophene-3-carboxylate

2-aminothiophenes derivative, Ethyl-2-amino-4-methyl thiophene-3-carboxylate (EAMC) has been synthesized, characterized, and investigated quantum chemically. It was experimentally investigated by different spectroscopic methods like- NMR (1H-NMR and 13C-NMR), FT-IR, and UV-Visible. B3LYP method and 6-311++G(d,p) basis set were employed for optimization of molecular structure and calculation of wave numbers of normal modes of vibrations and various other important parameters. Calculated bond lengths and angles were compared with the experimental bond lengths and Bond Angle Parameters. Optimized bond parameters and experimental bond parameters were found in good agreement. Complete potential energy distribution assignments were done successfully by VEDA. The HOMO/LUMO energy gap emphasizes adequate charge transfer happening within the molecule. A study of donor-acceptor interconnections was done via NBO analysis. MEP surface analysis was done to demonstrate charge distribution and reactive areas qualitatively in the molecule. The degree of relative localization of electrons was analyzed via ELF Diagram. The Fukui function analysis showed possible sites for attacks by different substituents. By using the TD-DFT method and PCM solvent model, the UV-Vis spectrum (gas, methanol, DMSO) and the maximum absorption wavelength was computed and compared with experimental data. 3D and 2D intermolecular interactions in the crystal were analyzed via Hirshfeld surface analysis and fingerprint plots reveal that the EAMC crystal was stabilized by H--H/H--H/C--H bond formation. The molecular docking was done with 7 different protein receptors on the molecule to find the best ligand-protein interactions. Molecular dynamic simulations and MMGBSA calculations were also carried out to find out the best binding of the ligand with the protein.Communicated by Ramaswamy H. Sarma.

Experimental and theoretical study on the regioselective bis- or polyalkylation of 6-amino-2-mercapto-3H-pyrimidin-4-one using zeolite nano-gold catalyst and a quantum hybrid computational method

The synthetic utility of 6-amino-2-mercapto-3H-pyrimidin-4-one 3 as building blocks for new poly (pyrimidine) by alkylation using the bis(halo) compounds and zeolite nano-gold as a catalyst was investigated. Furthermore, the experimental findings by the theoretical Density functional theory (DFT) computations at the DFT/B3LYP level of theory, utilizing the 6-311++G (d,p) basis set in the gas phase, were used to investigate the distinct phases for Regio isomer 11a & 12a and 11b & 12b compounds was fair and of good quality. The stability of the 12a and 12b phases is higher than the other Regio isomer 11a and 11b phases, according to DFT modelling. By computing HOMO and LUMO pictures, the electronic parameters: dipole moment of these compounds in the ground state were theoretically investigated. Non-linear optical (NLO) characteristics and quantum chemical parameters were examined using frontier molecular orbital (FMO) analysis. Natural bond orbital analysis was used to characterize the charge transfer of the electron density in the investigated compounds (NBO). The molecular electrostatic potential surfaces (MEPS) plots have been generated, and absorption spectral analysis in different solvents has been theoretically and experimentally examined to better understand the reactivity spots. At the B3LYP/6-311G (d,p) level of theory, thermodynamic properties were also calculated. Finally, DFT calculations were used to connect the structure-activity relationship (SAR) with real antibacterial results for compounds 12a and 12b.

Deep Eutectic Solvents or Eutectic Mixtures? Characterization of Tetrabutylammonium Bromide and Nonanoic Acid Mixtures

Deep eutectic solvents have quickly attracted the attention of researchers because they better meet the requirements of green chemistry and thus have the potential to replace conventional hazardous organic solvents in some areas. To better understand the nature of these mixtures, as well as expand the possibilities of their use in different industries, a detailed examination of their physical properties, such as density, viscosity, the nature of the interactions between their constituents, the phase diagrams, depression of their melting point, and interpretation of these results is necessary. In this work, the mixtures of tetrabutylammonium bromide (TBAB) and nonanoic acid (NA) in different molar ratios are theoretically and experimentally investigated by applying a phase diagram constructed on the basis of differential scanning calorimetry measurements and COSMO-RS model. Spectral properties are investigated based on Fourier transform infrared spectroscopy and density functional theory. The observed eutectic point indicates the formation of a DES in the TBAB−NA system in a 1:2 molar ratio. This is due to the presence of hydrogen bonds between the carboxyl group from the NA molecule and the bromine atom from the TBAB molecule. Other eutectic mixtures are most likely the solutions of TBAB in NA, in which hydrogen bonds predominate between acid molecules.

Synthesis, FT-IR, structural, thermochemical, electronic absorption spectral, and NLO analysis of the novel 10-methoxy-10H-furo[3,2-g]chromeno[2,3-b][1,3]thiazolo[5,4-e]pyridine-2,10(3H)-dione (MFCTP): a DFT/TD-DFT study

Chemical transformation of 4-methoxy-5-oxo-5H-furo[3,2-g]chromene-6-carbonitrile (1) with 1,3-thiazolidine-2,4-dione (2) in boiling ethanol containing piperidine afforded the novel 10-methoxy-10H-furo[3,2-g]chromeno[2,3-b][1,3]thiazole[5,4-e]pyridine-2,10(3H)-dione (3, MFCTP). The chemical structure of the synthesized compound was established via elemental analysis and spectral data. FT-IR spectroscopy was performed in the range of 400-4000 cm-1 for the vibrational spectral analysis of MFCTP. The GIAO method was employed to calculate the values of 1H and 13C NMR chemical shifts theoretically, which were consistent with the experimental chemical shifts. The molecule (3, MFCTP) has two stable structures, as determined from the potential energy curve. The S1 structure is the most stable conformer of (3, MFCTP) according to the computational results. The density functional theory (DFT) and ab initio HF calculations and different basis set combinations based on the structure optimizations and normal coordinate force field were interpreted with the aid of the molecular structure, fundamental vibrational frequencies, and intensities of the vibrational bands. The potential energy distribution (PED) was determined based on the complete vibrational wavenumber assignments. The calculated spectra of the title compound were in agreement with the observed spectra. The scaled B3LYP/6-311++G(d,p) results exhibited better agreement with the experimental values compared to the other method used. The time-dependent density functional theory (TD-DFT) was employed to calculate the energy and oscillator strength and supplement the experimental findings. Also, it was performed and the results interpreted the molecular electrostatic potential, nonlinear optical and thermodynamic properties, and Mulliken and natural charges of the title compound. DFT calculations were performed to study the structure-activity relationship (SAR) and compared with the experimental antimicrobial results for compound (3, MFCTP).

Quantum mechanical and spectroscopic (FT-IR, FT-Raman) study, NBO analysis, HOMO-LUMO, first order hyperpolarizability and molecular docking study of methyl[(3R)-3-(2-methylphenoxy)-3-phenylpropyl]amine by density functional method

Quantum chemical techniques such as density functional theory (DFT) have become a powerful tool in the investigation of the molecular structure and vibrational spectrum and are finding increasing use in application related to biological systems. The Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) techniques are employed to characterize the title compound. The vibrational frequencies were obtained by DFT/B3LYP calculations with 6-31G(d,p) and 6-311++G(d,p) as basis sets. The geometry of the title compound was optimized. The vibrational assignments and the calculation of Potential Energy Distribution (PED) were carried out using the Vibrational Energy Distribution Analysis (VEDA) software. Molecular electrostatic potential was calculated for the title compound to predict the reactive sites for electrophilic and nucleophilic attack. In addition, the first-order hyperpolarizability, HOMO and LUMO energies, Fukui function and NBO were computed. The thermodynamic properties of the title compound were calculated at different temperatures, revealing the correlations between heat capacity (C), entropy (S) and enthalpy changes (H) with temperatures. Molecular docking studies were also conducted as part of this study. The paper further explains the experimental results which are in line with the theoretical calculations and provide optimistic evidence through molecular docking that the title compound can act as a good antidepressant. It also provides sufficient justification for the title compound to be selected as a good candidate for further studies related to NLO properties.

Synthesis and dynamics of a novel proton transfer complex containing 3,5-dimethylpyrazole as a donor and 2,4-dinitro-1-naphthol as an acceptor: crystallographic, UV-visible spectrophotometric, molecular docking and Hirshfeld surface analyses

A CT complex is synthesized and characterized by spectral and crystallographic techniques. The Hirshfeld and molecular docking studies are also performed.

Indole-containing new types of dyes and their UV-vis and NMR spectra and electronic structures: Experimental and theoretical study

Indole containing dyes were synthesized via a simple method with high yield. These molecules have different colors and UV-vis spectra of them were recorded. Impact of solvents on absorbances was investigated and it was observed that basic solvent such as DMF and pyridine have blue shift. TD-DFT calculations were done and results were compared with experimental data. NMR data of molecules were analyzed and tautomeric forms of colorants and their ratio were determined. It was find out that two tautomers might be formed in solution, called indole and indolenine form. HOMO-LUMO and energy gaps were calculated and plotted. Furthermore, molecular electrostatic potentials were simulated to find out electrophilic and nucleophilic regions.

Molecular structure, spectroscopic characterization, HOMO and LUMO analysis of 3,3'-diaminobenzidine with DFT quantum chemical calculations

In this work, infrared, Raman and UV spectra of 3,3'-diaminobenzidine (3,3-DAB) were carried out by using density functional theory (DFT)/B3LYP method with 6-311G(d,p) basis set. FT-IR and FT-Raman spectra were recorded in the region 4000-400 and 4000-50 cm(-1), respectively. The geometrical parameters, energies and wavenumbers were obtained and fundamental vibrations were assigned on the basis of the potential energy distribution (PED) of the vibrational modes. The UV spectrum of the investigated compound was recorded in the range of 200-400 nm in ethanol and water solutions. The electronic properties, such as excitation energies, absorption wavelengths, HOMO and LUMO energies were performed by DFT/B3LYP approach and the results were compared with experimental observations. Thermodynamic properties, Mulliken atomic charges and molecular electrostatic potential (MEP) were calculated for the title molecule. Also the nonlinear optical properties of 3,3-DAB molecule were explored theoretically. As a result, the calculated results were compared with the observed values and generally found to be in good agreement.

Spectroscopic investigation (FTIR spectrum), NBO, HOMO-LUMO energies, NLO and thermodynamic properties of 8-Methyl-N-vanillyl-6-nonenamideby DFT methods

Capsicum a hill grown vegetable is also known as red pepper or chili pepper. Capsaicin(8-Methyl-N-vanillyl-6-nonenamide) is the active component in chili peppers, which is currently used in the treatment of osteoarthritis, psoriasis and cancer. Fourier transform infrared (FT-IR) spectrum of Capsaicin in the solid phase were recorded in the region 4000-400 cm(-1) and analyzed. The vibrational frequencies of the title compound were obtained theoretically by DFT/B3LYP calculations employing the standard 6-311++G(d,p) basis set and were compared with Fourier transform infrared spectrum. Complete vibrational assignment analysis and correlation of the fundamental modes for the title compound were carried out. The vibrational harmonic frequencies were scaled using scale factor, yielding a good agreement between the experimentally recorded and the theoretically calculated values. Stability of the molecule arising from hyper conjugative interactions, charge delocalization and intra molecular hydrogen bond-like weak interaction has been analyzed using Natural bond orbital (NBO) analysis by using B3LYP/6-311++G(d,p) method. The results show that electron density (ED) in the σ∗ and π∗ antibonding orbitals and second-order delocalization energies E (2) confirm the occurrence of intra molecular charge transfer (ICT) within the molecule. The dipole moment (μ), polarizability (α) and the hyperpolarizability (β) values of the molecule has been computed. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated.

The spectroscopic (FT-IR, UV-vis), Fukui function, NLO, NBO, NPA and tautomerism effect analysis of (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile

A new o-hydroxy Schiff base, (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile was isolated and investigated by experimental and theoretical methodologies. The solid state molecular structure was determined by X-ray diffraction method. The vibrational spectral analysis was carried out by using FT-IR spectroscopy in the range of 4000-400cm(-)(1). Theoretical calculations were performed by density functional theory (DFT) method using 6-31G(d,p) basis set. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The UV-vis spectrum of the compound was recorded in the region 200-800 nm in several solvents and electronic properties such as excitation energies, and wavelengths were calculated by TD-DFT/B3LYP method. The most prominent transitions were corresponds to π→π∗. Hybrid density functional theory (DFT) was used to investigate the enol-imine and keto-amine tautomers of titled compound. The titled compound showed the preference of enol form, as supported by X-ray and spectroscopic analysis results. The geometric and molecular properties were compaired for both enol-imine and keto-amine forms. Additionally, geometry optimizations in solvent media were performed with the same level of theory by the integral equation formalism polarizable continuum (IEF-PCM). Stability of the molecule arises from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed using natural bond orbital (NBO) analysis. Mulliken population method and natural population analysis (NPA) have been studied. Also, condensed Fukui function and relative nucleophilicity indices calculated from charges obtained with orbital charge calculation methods (NPA). Molecular electrostatic potential (MEP) and non linear optical (NLO) properties are also examined.

Molecular structure and vibrational analysis of Trifluoperazine by FT-IR, FT-Raman and UV-Vis spectroscopies combined with DFT calculations

The complete vibrational assignment and analysis of the fundamental vibrational modes of Trifluoperazine (TFZ) was carried out using the experimental FT-IR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G (d,p) basis set. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. The HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as first hyperpolarizability of TFZ have been computed using B3LYP quantum chemical calculation.

Quantum mechanical study and spectroscopic (FT-IR, FT-Raman, (13)C, (1)H) study, first order hyperpolarizability, NBO analysis, HOMO and LUMO analysis of 2-acetoxybenzoic acid by density functional methods

In this work, colorless crystals of 2-acetoxybenzoic acid were grown by slow evaporation method and the FT-IR and FT-Raman spectra of the sample were recorded in the region 4000-500cm(-1) and 4000-100cm(-1) respectively. Molecular structure is optimized with the help of density functional theory method (B3LYP) with 6-31+G(d,p), 6-311++G(d,p) basis sets. Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ(∗) antibonding orbitals and E(2) energies confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis following the scaled quantum mechanical force field (SQMFF) methodology. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO method. Mulliken population analysis on atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule.

Molecular structure and vibrational spectroscopic studies on 2-furanacetic acid monomer and dimer

In this work, molecular geometries and fundamental vibrational frequencies of 2-furanacetic acid (2FAA) and its hydrogen bonded dimer were investigated using DFT/B3LYP method with 6-311++G(d,p) as basis set. The FT-infrared and FT-Raman spectra of the 2FAA compound were recorded in the region 4000-400 cm(-1). The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. Complete vibrational assignments and analysis of the fundamental modes of monomer and dimer structures were performed on the basis of the potential energy distribution (PED) calculations. A study on the electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Molecular stability arising from hyperconjugative interactions and charge delocalization has been analyzed using Natural Bond Orbital (NBO) analysis. Topological parameters such an electron density and its Laplacian at bond critical points (BCP) of O-H and O⋯H contact bonds were analyzed in details with the help of the atoms in molecules (AIM) approach in order to study the intermolecular hydrogen bonding. The nonlinear optical properties of the title molecule have been investigated. Moreover, molecular electrostatic potential (MEP) surface was plotted for predicting sites and relative reactivities towards electrophilic and nucleophilic attack. The nonlinear optical properties were reported and compared with that of the urea. The thermodynamic properties like heat capacity, entropy, and enthalpy have been calculated for the molecule at different temperatures.

Experimental, quantum chemical and NBO/NLMO investigations of pantoprazole

The complete vibrational assignment and analysis of the fundamental modes of pantoprazole (PPZ) was carried out using the experimental FT-IR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G (d, p) basis set. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of PPZ have been computed using B3LYP quantum chemical calculation. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.

Experimental (FT-IR, FT-Raman, UV and NMR) and quantum chemical studies on molecular structure, spectroscopic analysis, NLO, NBO and reactivity descriptors of 3,5-Difluoroaniline

Comprehensive investigation of geometrical and electronic structure in ground as well as the first excited state of 3,5-Difluoroaniline (C6H5NF2) was carried out. The experimentally observed spectral data (FT-TR and FT-Raman) of the title compound was compared with the spectral data obtained by DFT/B3LYP method using 6-311++G(d,p) basis set. The molecular properties like dipole moment, polarizability, first static hyperpolarizability, molecular electrostatic potential surface (MEPs), and contour map were calculated to get a better insight of the properties of the title molecule. Natural bond orbital (NBO) analysis was applied to study stability of the molecule arising from charge delocalization. UV-Vis spectrum of the title compound was also recorded and the electronic properties, such as Frontier orbitals and band gap energies were measured by TD-DFT approach. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. Global and local reactivity descriptors were computed to predict reactivity and reactive sites on the molecule. (1)H and (13)C NMR spectra by using gauge including atomic orbital (GIAO) method of studied compound were compared with experimental data obtained. Moreover, the thermodynamic properties were evaluated.

Vibrational (FT-IR and FT-Raman), electronic (UV-Vis), NMR (1H and 13C) spectra and reactivity analyses of 4,5-dimethyl-o-phenylenediamine

The structure of 4,5-dimethyl-o-phenylenediamine (C8H12N2, DMPDA) was investigated on the basis of spectroscopic data and theoretical calculations. The sterochemical structure was determined by FT-IR, FT-Raman, UV, 1H and 13C NMR spectra. An experimental study and a theoretical analysis were associated by using the B3LYP method with Gaussian09 package program. FT-IR and FT-Raman spectra were recorded in the region of 4000-400 cm(-1) and 4000-10 cm(-1), respectively. The vibrational spectra were calculated by DFT method and the fundamental vibrations were assigned on the basis of the total energy distribution (TED), calculated with scaled quantum mechanics (SQM) method with Parallel Quantum Solutions (PQS) program. The UV absorption spectrum of the compound that dissolved in ethanol solution were recorded in the range of 190-400 nm. Total density of state (TDOS) and partial density of state (PDOS) of the DMPDA in terms of HOMOs and LUMOs were calculated and analyzed. Chemical shifts were reported in ppm relative to tetramethylsilane (TMS) for 1H and 13C NMR spectra. The compound was dissolved in dimethyl sulfoxide (DMSO). Also, 1H and 13C chemical shifts calculated using the gauge independent atomic orbital (GIAO) method. Mullikan atomic charges and other thermo-dynamical parameters were investigated with the help of B3LYP (DFT) method using 6-311++G** basis set. On the basis of the thermodynamic properties of the title compound at different temperatures have been carried out, revealing the correlations between heat capacity (C), entropy (S), enthalpy changes (H) and temperatures. The optimized bond lengths, bond angles, chemical shifts and vibrational wavenumbers showed the best agreement with the experimental results.

Experimental and theoretical spectroscopic analysis, HOMO-LUMO, and NBO studies of cyanuric chloride

The vibrational spectral analysis of cyanuric chloride was carried out by using FT-Raman and FT-IR spectra in the range 100-4000cm(-1) and 400-4000cm(-1) respectively. The structure optimization was done and structural characteristics were determined by Density Functional Theory (B3LYP) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The vibrational wavenumbers have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of the molecule has been made on the basis of the calculated Potential Energy Distribution (PED). The Natural bonding orbital (NBO) analysis performed to confirm the stability of the molecule arising from hyper conjugation and delocalization. The Mulliken atomic charges were also calculated. The computed HOMO-LUMO energy gap shows that charge transfer occurs within the molecule. The thermodynamic properties at different temperatures have been calculated from the vibrational analysis.

Vibrational and UV spectra, first order hyperpolarizability, NBO and HOMO-LUMO analysis of 4-chloro-N-(2-methyl-2,3-dihydroindol-1-yl)-3-sulfamoyl-benzamide

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 4000-100 cm(-1) and 4000-400 cm(-1), respectively, for 4-chloro-N-(2-methyl-2,3-dihydroindol-1-yl)-3-sulfamoyl-benzamide (C16H16O3N3SCl) molecule. Theoretical calculations were performed by density functional theory (DFT) method using 6-31G(d,p) and 6-311G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (β0) and related properties (μ, α, and Δα) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The UV-vis spectrum of the compound was recorded in the region 200-400 nm in ethanol and electronic properties such as excitation energies, oscillator strength and wavelength were calculated by TD-DFT/B3LYP method. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures.

Quantum-chemical (DFT, MP2) and spectroscopic studies (FT-IR and UV) of monomeric and dimeric structures of 2(3H)-Benzothiazolone

Molecular geometry and vibrational wavenumbers of 2(3H)-Benzothiazolone (C7H5NSO, HBT) was investigated using density functional (DFT/B3LYP) method with 6-311+G(d,p) basis set. The vibrational wavenumbers are found to be in good agreement with experimental FT-IR spectra. Hydrogen-bonded dimer of HBT, optimized by counterpoise correction, was studied by MP2 and DFT/B3LYP at the 6-311+G(d,p) level and the effects of molecular association through NH---O hydrogen bonding were discussed. A detailed analysis of the nature of the hydrogen bonding, using topological parameters, such as electronic charge density, Laplacian, kinetic and potential energy density evaluated at bond critical points (BCP) has also been presented. The UV absorption spectra of the compound dissolved in ethanol and chloroform solutions were recorded in the range of 200-600 nm. The UV-vis spectrum of the title molecule was also calculated using TD-DFT method. The calculated energy and oscillator strength almost exactly reproduce the experimental data. Total and partial density of state (TDOS, PDOS) of the HBT in terms of HOMOs and LUMOs and molecular electrostatic potential (MEP) were calculated and analyzed. The electric dipole moment, polarizability and the first static hyper-polarizability values for HBT were calculated at the DFT/B3LYP with 6-311+G(d,p) basis set. The results also show that the HBT molecule may have nonlinear optical (NLO) comportment with non-zero values. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization was analyzed using natural bond orbital (NBO) analysis.

Molecular structure, intramolecular hydrogen bonding and vibrational spectral investigation of 2-fluoro benzamide--a DFT approach

The FTIR and FT-Raman spectra of 2-fluoro benzamide (2FBA) have been recorded in the region 4000-400 and 4000-100 cm(-1), respectively. The structuralanalysis, hydrogen bonding, optimized geometry, frequency and intensity of the vibrational bands of 2FBA were obtained by the density functional theory (DFT) with complete relaxation in the potential energy surface using 6-31G** basis set. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The (13)C NMR spectra have been recorded and (13)C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method and their respective linear correlations were obtained. The electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The Mulliken charges, the values of electric dipole moment (μ) of the molecule were computed using DFT calculations. The change in electron density (ED) in the σ* antibonding orbitals and stabilization energies E(2) have been calculated by natural bond (NBO) analysis to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions.

An experimental and theoretical study of the vibrational spectra and structure of Isosorbide dinitrate

The present work aims at exploring the vibrational spectra of Isosorbide dinitrate and its chemical activity in a five membered ring system. The FT-IR and FT-Raman spectral studies of the Isosorbide dinitrate (ISDN) were carried out. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of ISDN have been calculated using B3LYP density functional theory (DFT) with 6-31G(d,p) as basis set. The calculated HOMO and LUMO energies and density of states (DOS) show the chemical activity of the molecule. Good correlations between the experimental (1)H and (13)C NMR chemical shifts in methanol-d and calculated GIAO shielding tensors were found. The potential energy surface was studied using the DFT method.

Electronic absorption, vibrational spectra, nonlinear optical properties, NBO analysis and thermodynamic properties of N-(4-nitro-2-phenoxyphenyl) methanesulfonamide molecule by ab initio HF and density functional methods

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 4000-100 cm(-1) and 4000-400 cm(-1), respectively, for N-(4-nitro-2-phenoxyphenyl) methanesulfonamide molecule. Theoretical calculations were performed by ab initio RHF and density functional theory (DFT) method using 6-31G(d,p) and 6-311G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (β0) and related properties (μ, α and Δα) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the σ(*) and π(*) anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV-vis spectrum of the compound was recorded in the region 200-500 nm in ethanol and electronic properties such as excitation energies, oscillator strength and wavelength were calculated by TD-DFT/B3LYP, CIS and TD-HF methods using 6-31G(d,p) basis set. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature.

Spectroscopic (FT-IR/FT-Raman) and computational (HF/DFT) investigation and HOMO/LUMO/MEP analysis on 2-amino-4-chlorophenol

The spectra (FT-IR and FT-Raman) of the present compound; 2-amino-4-chlorophenol (2A4CP) were recorded in the range of 4000-100 cm(-1). All the computational calculations were made in the ground state using the HF and DFT (B3LYP and B3PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets. From potential energy surface calculation, there are two conformers, Rot-1 and Rot-2 for this molecule. The computational results detected that Rot-1 form is the most stable conformer. Making use of the recorded data, the complete vibrational assignments were made and analysis of the observed fundamental bands of molecule is carried out. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQMs) method and PQS program. The shifting of the frequencies in the vibrational pattern of the title molecule due to the substitutions; NH(2) and Cl were deeply investigated by the vibrational analysis. Moreover, (13)C NMR and (1)H NMR chemical shifts were calculated by using the gauge independent atomic orbital (GIAO) method with HF/B3LYP/B3PW91 methods with 6-311++G(d,p). A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. Besides frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) was performed. NLO properties and Mulliken charges of the 2A4CP were also calculated and interpreted. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase.

FT-IR, FT-Raman and UV spectral investigation: computed frequency estimation analysis and electronic structure calculations on 1-bromo-2-methylnaphthalene

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 100-4000 cm(-1) and 400-4000 cm(-1) respectively, for 1-bromo-2-methylnaphthalene (C11H9Br) molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based density functional theory (DFT) and ab initio HF methods with different basis sets combinations. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated vibrational spectra of the title compound, which show excellent agreement with observed spectra. The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. In addition, molecular electrostatic potential and nonlinear optical and thermodynamic properties of the title compound were performed. Mulliken charges and NBOs of the title molecule were also calculated and interpreted.

Spectroscopic (FT-IR, FT-Raman, UV and NMR) investigation and NLO, HOMO-LUMO, NBO analysis of organic 2,4,5-trichloroaniline

In this work, the experimental and theoretical study on the molecular structure and vibrational spectra of 2,4,5-trichloroaniline (C(6)H(4)NCl(3), abbreviated as 2,4,5-TClA) were studied. The FT-IR and FT-Raman spectra were recorded. The molecular geometry and vibrational frequencies in the ground state were calculated by using the Hartree-Fock (HF) and density functional theory (DFT) methods (B3LYP) with 6-311++G(d,p) basis set. Comparison of the observed fundamental vibrational frequencies of 2,4,5-TClA with calculated results by HF and DFT indicates that B3LYP is superior to HF method for molecular vibrational problems. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The theoretically predicted FT-IR and FT-Raman spectra of the title molecule have been constructed. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. Besides, molecular electrostatic potential (MEP) and thermodynamic properties were performed. The electric dipole moment (μ) and the first hyperpolarizability (β) values of the investigated molecule were computed using ab initio quantum mechanical calculations. The calculated results also show that the 2,4,5-TClA molecule may have microscopic nonlinear optical (NLO) behavior with non-zero values. Mulliken atomic charges of 2,4,5-TClA was calculated and compared with aniline and chlorobenzene molecules. The (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results.

Spectroscopic (infrared, Raman, UV and NMR) analysis, Gaussian hybrid computational investigation (MEP maps/HOMO and LUMO) on cyclohexanone oxime

In the present analysis, FT-IR/FT-Raman spectra of the cyclohexanone oxime (CHO, C(6)H(11)NO) are recorded. The observed vibrational frequencies are assigned and the computational calculations are carried out by HF and DFT (B3LYP and B3PW91) methods with 6-311++G(d,p) basis set and the corresponding results are tabulated. In order to yield good coherence with observed values, the calculated frequencies are scaled by appropriate scale factors. The complete assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The alternation of structure of cyclohexanone due to the substitution of NOH is investigated. The vibrational sequence pattern of the molecule related to the substitutions is analyzed. Comparison of the observed fundamental vibrational frequencies of CHO and calculated results by density functional (B3LYP and B3PW91) and HF methods indicates that B3LYP is superior to the scaled HF and B3PW91 approach for molecular vibrational problems. Moreover, (13)C NMR and (1)H NMR chemical shifts are calculated by using the gauge independent atomic orbital (GIAO) method with HF/B3LYP/B3PW91 methods and the same basis set. A study on the electronic properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, are performed by HF and DFT methods. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Besides frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) was performed. NLO properties and Mulliken charges of the CHO was also calculated and interpreted. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures are calculated in gas phase.

The spectroscopic (FT-Raman, FT-IR, UV and NMR), molecular electrostatic potential, polarizability and hyperpolarizability, NBO and HOMO-LUMO analysis of monomeric and dimeric structures of 4-chloro-3,5-dinitrobenzoic acid

Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 4-chloro-3,5-dinitrobenzoic acid (CDNBA) were carried out by using density functional (DFT/B3LYP) method with 6-311++G(d,p) as basis set. To determine lowest-energy molecular conformation of the title molecule, the selected torsion angle is varied every 10° and molecular energy profile is calculated from 0° to 360°. The optimized geometrical parameters obtained by DFT calculations are in good conformity with single crystal XRD data. The FT-IR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational wavenumbers as well as their intensities were calculated and a good agreement between observed and scaled calculated wavenumbers has been achieved. The electric dipole moment, polarizability and the first hyperpolarizability values of the CDNBA have been calculated at the same level of theory and basis set. The calculation results also show that the CDNBA molecule may has nonlinear optical (NLO) behavior with non-zero values. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. Ultraviolet-visible (UV) spectrum of the title molecule has also been calculated using CIS and TD-DFT methods. The calculated energy and oscillator strength almost exactly reproduce the experimental data. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. The thermodynamic properties of the studied compound at different temperatures were calculated.

FT-IR, FT-Raman and UV spectral investigation: computed frequency estimation analysis and electronic structure calculations on chlorobenzene using HF and DFT

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 100-4000 cm(-1) and 400-4000 cm(-1) respectively, for the title molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree Fock (HF) and density functional theory (DFT) method and different basis sets combination. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The effects due to the substitution of halogen bond were investigated. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), and thermodynamic properties were performed. The thermodynamic properties of the title compound at different temperatures have been calculated, revealing the correlations between heat capacity (C), entropy (S), and enthalpy changes (H) and temperatures.

FT-IR, FT-Raman and UV spectral investigation; computed frequency estimation analysis and electronic structure calculations on 1-nitronaphthalene

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 100-4000cm(-1) and 400-4000cm(-1) respectively, for 1-nitronaphthalene (C(10)H(7)NO(2)) molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based density functional theory (DFT) and ab initio HF methods and different basis sets combination. The complete vibrational assignments of wavenumbers were made on the basis of total energy distribution (TED). The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) complements with the experimental findings. Thermodynamic properties of the title compound at different temperatures have been calculated. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) were performed.

Vibrational spectroscopy (FT-IR and FT-Raman) investigation, and hybrid computational (HF and DFT) analysis on the structure of 2,3-naphthalenediol

The FT-IR and FT-Raman vibrational spectra of 2,3-naphthalenediol (C(10)H(8)O(2)) have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1) in solid phase. A detailed vibrational spectral analysis has been carried out and the assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-Fock (HF) and DFT (LSDA and B3LYP) methods with 6-31+G(d,p) and 6-311+G(d,p) basis sets. There are three conformers, C1, C2 and C3 for this molecule. The computational results diagnose the most stable conformer of title molecule as the C1 form. The isotropic computational analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by HF and DFT methods. Comparison of the simulated spectra provides important information about the capability of computational method to describe the vibrational modes. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and Frontier molecular orbital energies, are performed by time dependent DFT approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated. The statistical thermodynamic properties (standard heat capacities, standard entropies, and standard enthalpy changes) and their correlations with temperature have been obtained from the theoretical vibrations.

Molecular structure, vibrational spectral studies of pyrazole and 3,5-dimethyl pyrazole based on density functional calculations

In this work, the experimental and theoretical vibrational spectra of pyrazole (PZ) and 3,5-dimethyl pyrazole (DMP) have been studied. FTIR and FT-Raman spectra of the title compounds in the solid phase are recorded in the region 4000-400 cm(-1) and 4000-50 cm(-1), respectively. The structural and spectroscopic data of the molecules in the ground state are calculated using density functional methods (B3LYP) with 6-311+G** basis set. The vibrational frequencies are calculated and scaled values are compared with experimental FTIR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete vibrational assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SM) method. 13C and 1H NMR chemical shifts results are compared with the experimental values.

Experimental (FT-IR and FT-Raman), electronic structure and DFT studies on 1-methoxynaphthalene

In this work, FT-IR and FT-Raman spectra of 1-methoxynapthalene (C(11)H(10)O) have been reported in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. Density functional method (DFT) has been used to calculate the optimized geometrical parameters, atomic charges, vibrational wavenumbers and intensity of the vibrational bands. The vibrational frequencies have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field calculations are based on density functional theory (DFT) method with B3LYP/3-21G, B3LYP/6-31G, B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers are made on the basis of potential energy distribution (PED). The optimized geometric parameters are compared with experimental values of naphthoic acid. The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The effects due to the substitutions of methyl group and carbon-oxygen bond are also investigated. A study on the electronic properties, such as excitation energies and wavelengths, were performed by time-dependent DFT (TD-DFT) approach. HOMO and LUMO energies are calculated that these energies show charge transfer occurs within the molecule.

FT-IR, FT-Raman, NMR spectra and DFT calculations on 4-chloro-N-methylaniline

In this work, the vibrational spectral analysis was carried out by using FT-IR and FT-Raman spectroscopy in the range 400-4000 and 50-3500cm(-1) respectively, for the title molecule. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method using 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 are found to be in good agreement. The complete assignments of all the vibrational mode were performed on the basis of the total energy distributions (TED). (13)C and (1)H NMR chemical shifts results were given and are in agreement with the corresponding experimental values. The theoretically constructed FT-IR and FT-Raman spectra exactly coincides with experimental one.