RESUMEN
Benzimidazoles are bicyclic heteroatomic molecules. Polycyclic heteroatomic molecules have extensive coupling of different modes leading to strong coupling of force constants associated with the various chemical bonds of the molecules. To carry out a detailed vibrational spectroscopic analysis of such a bicyclic heteroatomic molecule, FT-IR and FT-Raman spectra of 2-chloro benzimidazole (CBZ) have been recorded in the condensed phase. Density Functional Theory calculations in the B3LYP/6-31G(*) level have been carried out to determine the optimized geometry and vibrational frequencies. In order to obtain a close agreement between theoretical and observed frequencies and hence to perform a reliable assignment, the theoretical DFT force field was transformed from Cartesian to local symmetry co-ordinates and then scaled empirically using SQM methodology. The SQM treatment resulted in a RMS deviation of 9.4 cm(-1). For visual comparison, the observed and calculated spectra are presented on a common wavenumber scale. From the NBO analysis, the electron density (ED) charge transfers in the σ(*) and π(*) antibonding orbitals and second order delocalization energies E((2)) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The calculated Homo and Lumo energies show that charge transfer occurs within the molecule. The results obtained from the vibrational, NBO and HOMO-LUMO analyses have been properly tabulated.
Asunto(s)
Bencimidazoles/química , Modelos Químicos , Espectroscopía Infrarroja por Transformada de Fourier , Espectrometría Raman , Electrones , Modelos MolecularesRESUMEN
Organic 2,5-dichloroanilinium picrate crystal was grown by using slow evaporation solution technique. The lattice parameter was estimated by powder X-ray diffraction. The absence of absorption at around Nd:YAG fundamental wavelength was confirmed by ultraviolet-visible absorption study. The vibrational analyses confirm the various functional groups present in the grown crystal. The NMR study confirms the presence of chemical environment of hydrogen in the title crystal. The thermogravimetric (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) traces reveals the thermal stability of the compound. The second harmonic generation (SHG) of the crystal was confirmed by Kurtz Perry powder technique. The theoretical studies such as first-order hyperpolarizability (ß), molecular orbitals, electronic excitation and electrostatic potential (ESP) were performed using Gaussian 03W software at HF/6-31G (d) level.
Asunto(s)
Compuestos de Anilina/química , Modelos Moleculares , Picratos/química , Absorción , Rastreo Diferencial de Calorimetría , Simulación por Computador , Cristalización , Electrones , Espectroscopía de Resonancia Magnética , Conformación Molecular , Solubilidad , Espectrofotometría Ultravioleta , Espectroscopía Infrarroja por Transformada de Fourier , Espectrometría Raman , Electricidad Estática , Termogravimetría , Difracción de Rayos XRESUMEN
The vibrational spectra of 4-bromo benzonitrile have been reported. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311+G basis set combination and were scaled using various scale factors which yielded a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra.
Asunto(s)
Simulación por Computador , Nitrilos/química , Teoría Cuántica , Modelos Biológicos , Modelos Químicos , Conformación Molecular , Análisis Espectral , VibraciónRESUMEN
The mid and far FTIR and Raman spectra were measured in the liquid state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) and standard B3LYP/6-311+G** basis set combination. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical (SQM) force field. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Unambiguous vibrational assignment of all the fundamentals was made using the total energy distribution (TED).
Asunto(s)
Aldehídos/análisis , Aldehídos/química , Naftalenos/análisis , Naftalenos/química , Espectrofotometría Infrarroja/métodos , Espectrometría Raman/métodos , Vibración , Carbono/química , Hidrógeno/química , Estructura MolecularRESUMEN
This work deals with the vibrational spectroscopy of 1-naphthyl acetic acid. The molecular vibrations of 1-naphthyl acetic acid (NAA) is investigated in polycrystalline sample, at room temperature, by Fourier transform infrared (FT-IR) and FT-Raman spectroscopy. In parallel, ab initio and various density functional (DFT) methods were used to determine the geometrical, energetic and vibrational characteristics of NAA. On the basis of B3LYP/6-311+G** method and basis set combinations, a normal mode analysis was performed to assign the various fundamental frequencies according to the total energy distribution (TED). Simulation of infrared and Raman spectra, utilizing the results of these calculations led to excellent overall agreement with observed spectral patterns by refinement of scale factors.
Asunto(s)
Ácidos Naftalenoacéticos/análisis , Espectroscopía Infrarroja por Transformada de Fourier/métodos , Espectrometría Raman/métodos , Vibración , Carbono/química , Simulación por Computador , Estructura Molecular , Ácidos Naftalenoacéticos/química , TemperaturaRESUMEN
The solid phase mid FTIR and FT Raman spectra of 2-naphthoic acid (NA) and 6-bromo-2-naphthoic acid (BNA) have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The fundamental vibrational frequencies and intensities of the vibrational bands were evaluated using density functional theory (DFT) using standard B3LYP method and 6-311+G** basis set combinations. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.
Asunto(s)
Bromo/química , Naftalenos/química , Vibración , Biología Computacional/métodos , Modelos Moleculares , Espectroscopía Infrarroja por Transformada de Fourier/métodos , Espectrometría Raman/métodosRESUMEN
The FTIR and FT-Raman spectra of 1-bromo 4-fluoronaphthalene have been recorded in the regions 4000-100 cm(-1) and 3500-100 cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis based on DFT (density functional theory) using standard B3LYP/6-311+G** basis set combination for the most optimized geometry. Normal coordinate calculations performed with the DFT force field and subsequently corrected by a recommended set of scale factors, yielded fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined.
Asunto(s)
Naftalenos/química , Vibración , Carbono/química , Simulación por Computador , Hidrógeno/química , Estructura Molecular , Espectrofotometría Infrarroja , Espectrometría Raman , EstereoisomerismoRESUMEN
The solid phase FTIR and Raman spectra of 6-methyl 1,2,3,4-tetrahydroquinoline (MTHQ) have been recorded in the regions 4000-100 and 3500-100 cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculations based on the density functional theory (DFT) using the standard B3LYP/6-311+G(**) basis set combination. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors.
Asunto(s)
Modelos Químicos , Quinolinas/química , Espectrometría Raman , Vibración , Conformación Molecular , Espectroscopía Infrarroja por Transformada de FourierRESUMEN
The solid phase FT-IR and FT-Raman spectra of 4-hydroxy quinazoline and 2-hydroxy benzimidazole have been recorded in the regions 4000-400 and 3500-100 cm-1, respectively. Theoretical information on the optimised geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of density functional theory using standard B3LYP/6-31G* level. This information was used in the assignment of the various fundamentals. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.
Asunto(s)
Bencimidazoles/química , Modelos Químicos , Quinazolinonas/química , Espectrometría Raman , Radical Hidroxilo/química , Espectroscopía Infrarroja por Transformada de Fourier , VibraciónRESUMEN
The vibrational spectra of 2,3-dihydroxy pyridine (DHP) and 2,4-dihyroxy-3-nitropyridine (DHNP) have been computed using B3LYP methodology and 6-31G** basis set. The solid phase FTIR and FT Raman spectra were recorded in the region 4000-400 and 3500-100 cm(-1), respectively. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors.
Asunto(s)
Nitrocompuestos/química , Piridinas/química , Espectroscopía Infrarroja por Transformada de Fourier , Espectrometría Raman , Estructura Molecular , Teoría Cuántica , VibraciónRESUMEN
The vibrational spectra of 3,4-diamino benzophenone (DABP) have been computed using B3LYP methodology and 6-31G* and 6-31G** basis sets. The solid phase FTIR and FT-Raman spectra were recorded in the region 4000-400 cm-1 and 3500-100 cm-1, respectively. A close agreement was achieved between the observed and calculated frequencies by employing normal coordinate calculations. The observed and simulated spectra were found to be well comparable.
Asunto(s)
Benzofenonas/química , Cetonas/análisis , Modelos Químicos , Fenilendiaminas , Teoría Cuántica , Espectroscopía Infrarroja por Transformada de Fourier , Espectrometría RamanRESUMEN
The solid phase FTIR and FT-Raman spectra of 4-chloro-5-fluoro-1,2-phenylenediamine (C(6)H(6)ClFN(2)) have been recorded in the region 4000-400 and 3500-100 cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculations based on the density functional theory (DFT) using the standard B3LYP/6-31G( *) method and basis set combination. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors.