Vibrational spectroscopic (FTIR and FT Raman) studies, first order hyperpolarizabilities and HOMO, LUMO analysis of p-toluenesulfonyl isocyanate using ab initio HF and DFT methods

The Fourier transform infrared (FTIR) and FT Raman spectra of p-toluenesulfonyl isocyanate (p-tosyl isocyanate) have been measured. The molecular geometry, vibrational frequencies, infrared intensities, Raman activities and atomic charges have been calculated by using ab initio HF and density functional theory calculation (B3LYP) with 6-311+G(d,p) basis set. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT Raman data. The thermodynamic functions of the title compound were also performed with the aid of HF/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory. Simulated FTIR and FT Raman spectra for p-tosyl isocyanate showed good agreement with the observed spectra. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The dipole moment (μ), polarizability (α) and the hyperpolarizability (β) values of the investigated molecule have been computed using HF and B3LYP methods.     

FT-Raman and FTIR spectra, assignments and ab initio calculations of 2-aminobenzyl alcohol

The Fourier transform Raman and Fourier transform infrared spectra of 2-aminobenzyl alcohol (2ABA) were recorded in the solid phase. Geometry optimizations were done with out any constraint and harmonic vibrational wave numbers and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and DFT levels invoking 6-31g** and 6-311+g(2d, p) basis sets and the results were compared with the experimental values. With the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range and the error obtained was in general very low. The appropriate theoretical spectrograms for the Raman and IR spectra of 2ABA were also constructed.     

Vibrational spectra and assignments of 5-amino-2-chlorobenzoic acid by ab initio Hartree-Fock and density functional methods

The Fourier transform Raman and Fourier transform infrared spectra of 5-amino-2-chlorobenzoic acid (5A2CBA) were recorded in the solid phase. Geometry opitimizations were done without any constraint and harmonic-vibrational wavenumber and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and DFT levels invoking 6-311G(d,p) basis set and the results are compared with the experimental values with the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrograms for the FTIR spectra of the title molecule were also constructed.     

Vibrational spectroscopy investigation using ab initio and density functional theory on p-anisaldehyde

The FTIR and FT Raman spectra of p-anisaldehyde has been recorded in the regions 4,000-400 and 3,500-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of p-anisaldehyde were obtained by ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The harmonic vibrational frequencies calculated have been compared with experimental FTIR and FT Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.     

FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular conformational analysis of 2,5-di-tert-butyl-hydroquinone

The purpose of finding conformer among six different possible conformers of 2,5-di-tert-butyl-hydroquinone (DTBHQ), its equilibrium geometry and harmonic wavenumbers were calculated by the B3LYP/6-31G(d,p) method. The infrared and Raman spectra of DTBHQ were recorded in the region 400-4000 cm(-1) and 50-3500 cm(-1), respectively. In addition, the IR spectra in CCl(4) at various concentrations of DTBHQ are also recorded. The computed vibrational wavenumbers were compared with the IR and Raman experimental data. Computational calculations at B3LYP level with two different basis sets 6-31G(d,p) and 6-311++G(d,p) are also employed in the study of the possible conformer of DTBHQ. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA 4 program. The general agreement between the observed and calculated frequencies was established.     

Vibrational spectral analysis and first hyperpolarizability studies of 1-bromonaphthalene based on ab initio and DFT methods

In this work, the experimental and theoretical vibrational spectra of 1-bromonaphthalene (1-BN) were studied. FTIR and FT Raman spectra 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 by using ab initio Hartree-Fock and density functional method (B3LYP) with the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FTIR and FT Raman spectra. The observed and calculated frequencies are 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. The optimized geometric parameters were calculated. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good nonlinear optical (NLO) behaviour. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the molecule.     

3,5-Difluorobenzonitrile: ab initio calculations,FTIR and Raman spectra

Geometry, vibrational wavenumbers and several thermodynamic parameters were calculated using ab initio quantum chemical methods for the 3,5-difluorobenzonitrile molecule. The results were compared with the experimental values. With the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and Raman spectra were analysed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range and the error obtained was in general very low. Using PEDs the contributions were determined for the different modes to each wavenumber. From the PED, it is apparent that the frequency corresponding to C[triple bond]N stretching contains 87% contribution from the C[triple bond]N stretching force constant and it mixes with the C-CN stretching mode 13 to the extent of 12%. Other general conclusions were also deduced.     

Vibrational spectra and quantum chemical calculations of 3,4-diaminobenzoic acid.

The Fourier Transform Raman and Fourier Transform infrared spectra of 3,4-diaminobenzoic acid (3,4-DABA) were recorded in the solid phase. Geometry optimizations were done without any constraint and harmonic-vibrational wave numbers and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and DFT levels invoking 6-311++G(d,p) basis set. The results were compared with the experimental values with the help of specific scaling procedures, the observed vibrational wavenumbers in FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrograms for the IR and Raman spectra of the title molecule were also constructed.     

Vibrational spectroscopy investigation using ab initio and density functional theory on 3′-chloropropiophenone and 3′-nitropropiophenone

The FTIR and FT Raman spectra of 3′-chloropropiophenone and 3′-nitropropiophenone have been recorded in the regions 4000–400 and 3500–100 cm^?1 respectively. The optimized geometry, frequency and intensity of the vibrational bands of 3′-chloropropiophenone and 3′-nitropropiophenone were obtained by ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-31G (d,p) basis set. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The harmonic vibrational frequencies calculated have been compared with experimental FTIR and FT Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed simulated spectrograms.     

Density functional theory study of the Fourier transform infrared and Raman spectra of Cu(II) bis-acetylacetone

Fourier transform infrared and Fourier transform Raman spectra of Cu(II) bis-acetylacetone have been obtained. The geometry, frequency and intensity of the vibrational bands of this compound and its 1,5-(13)C(2), 3-(13)C, 1,3,5-(13)C(3), 2,4-(13)C(2), (18)O(2) and 2,4-(13)C(2)-(18)O(2) derivatives were obtained by the density functional theory (DFT) with the B3LYP functional and using the 6-31G(*) and 3-21G(*) basis sets. The calculated frequencies are compared with the solid infrared and Raman spectra. All the measured infrared and Raman bands were interpreted in terms of the calculated vibrational modes. The percentage of deviation of the bond lengths and bond angles gives a good picture of the normal modes, and serves as a basis for the assignment of the wavenumbers. Most computed bands are predicted to be at higher wavenumbers than the experimental bands. The calculated geometrical parameters show slight differences compared with the experimental results. These differences can be explained by the different physical state of Cu(II) bis-acetylacetone. The DFT-B3LYP calculations assumed a free molecule in the gas phase. Analysis of the vibrational spectra indicates a strong coupling between the chelated ring modes.     

Molecular structure, vibrational spectroscopic, first-order hyperpolarizability and HOMO, LUMO studies of 2-aminobenzimidazole

In the present work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and HOMO-LUMO analysis of 2-aminobenzimidazole (2-ABD). The FTIR (400-4000 cm(-1)) and FT-Raman spectra (50-3500 cm(-1)) of 2-ABD were recorded. The molecular geometry, harmonic vibrational wavenumbers and bonding features of 2-ABD in the ground-state have been calculated by using the density functional B3LYP method with 6-311++G(d,p) and 6-31G(d) as basis sets. The energy and oscillator strength were calculated by time-dependent density functional theory (TD-DFT) result complements with the experimental findings. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule. Finally, the calculation results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the observed spectra.     

FT-IR, NIR-FT-Raman and gas phase infrared spectra of 3-aminoacetophenone by density functional theory and ab initio Hartree-Fock calculations

The gas phase infrared spectrum of 3-aminoacetophenone (3AAP) was measured in the range 5000-500cm(-1) and with a resolution of 0.5cm(-1). The Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectra of 3AAP were recorded in the solid phase. Geometry optimizations were done without any constraint and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and density functional theory (DFT) levels invoking 6-311G(2df 2p) basis set and the results are compared with the experimental values. Harmonic-vibrational wavenumber was also calculated for the minimum energy conformer at ab initio and DFT levels using 6-31G(d,p) basis set and the results are compared with related molecules. With the help of specific scaling procedures, the observed vibrational wavenumbers in gas phase, FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrogram for the FT-IR spectra of the title molecule is also constructed.     

Structures and vibrational frequencies of 2-naphthoic acid and 6-bromo-2-naphthoic acid based on density functional theory calculations

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.     

An experimental and theoretical study of vibrational spectra of picolinamide, nicotinamide, and isonicotinamide

The molecular structures and vibrational spectra of the three isomers of pyridinecarboxamide (picolinamide, nicotinamide, isonicotinamide) were calculated with the Density Functional Theory (DFT) method using the B3LYP function and the 6-31++G(d,p), Z2PolX, Z3PolX basis sets. The calculations were performed by using the Gaussian98W packet program set. The total energy distributions (TED) of the vibrational modes of these molecules were calculated by using the Scale 2.0 program and the vibrational modes of the molecules were determined. The Scaled Quantum Mechanical (SQM) method was used in the scaling procedure. In the experimental part of the study, the solid phase FT-IR and Micro Raman spectra of the three isomers of pyridinecarboxamide have been recorded in the range of 4000-650 and 1200-100 cm⁻¹, respectively. The calculated wavenumbers were compared to the corresponding experimental values. As a result, the observed bands of the three isomers of pyridinecarboxamide were assigned with good accuracy.     

Determination of structural and vibrational spectroscopic properties of 2-, 3-, 4-nitrobenzenesulfonamide using FT-IR and FT-Raman experimental techniques and DFT quantum chemical calculations

In this work, the molecular conformation and vibrational analysis of 2-, 3-, 4-nitrobenzenesulfonamide (abbreviated as 2-, 3-, 4-NBSA) were presented for the ground state using experimental techniques (FT-IR and FT-Raman) and density functional theory (DFT) employing B3LYP exchange correlation with the 6-311++G(d,p) basis set. The complete assignments of fundamental vibrations were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The effects of the nitro group substituent on the characteristic benzene sulfonamides bands in the spectra were discussed. Raman activities calculated by DFT method have been converted to the corresponding Raman intensities using Raman scattering theory. Optimized structure of compounds were interpreted and compared with the earlier reported experimental values for studied molecules. The observed and the calculated geometric parameters and vibrational wavenumbers were compared and found to be in good agreement.     

DFT and ab initio quantum chemical studies on p-cyanobenzoic acid

The Fourier transform infrared (FTIR) and FT-Raman spectra of p-cyanobenzoic acid (CBA) have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with theoretical wavenumbers obtained from ab initio HF and DFT-B3LYP gradient calculations employing 6-31G**, 6-311++G** and cc-pVTZ basis sets for the optimised geometry of the compound. The geometry and normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental data. The normal coordinate analysis was also carried out with ab initio force fields utilising Wilson's FG matrix method. The interactions of cyano and carboxylic acid groups with the skeletal vibrational modes were investigated.     

FT-IR, FT-Raman spectra and scaled quantum mechanical study of 2,3-dihydroxy pyridine and 2,4-dihyroxy-3-nitropyridine

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.     

Vibrational assignment of the normal modes of 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one via FTIR and Raman spectra, and ab inito calculations

Raman and FTIR spectra of 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one were recorded in the regions, 100-3300 and 400-4000 cm(-1), respectively. Vibrational frequencies and intensities of the fundamental modes of this hetrocyclic organic molecule were computed using ab initio as well as AM1 semiempirical molecular orbital methods. Ab initio calculations were carried out with basis set up to RHF/6-311G. Conformational studies regarding the effect of moving the methoxy group in the 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one molecule to a different position on the ring was also carried out. Observed vibrational wavenumbers were found to be mostly consistent with ab initio values. The most intense mode of vibration observed at 1250 cm(-1) in Raman spectra, also observed as a strong band in FTIR, was assigned as C-O stretching vibration in the methoxy group. Asymmetric stretching vibrations between CC and CN bonds was predicted as most intense mode by our ab initio calculation.     

Spectroscopic (FTIR and FT Raman) analysis and vibrational study on 2,3-dimethyl naphthalene using ab-initio HF and DFT calculations

A combined experimental and theoretical study on molecular and vibrational structure of 2,3-dimethyl naphthalene (2,3-DMN) has been undertaken in the present work. The FTIR and FT Raman spectra of 2,3-DMN were recorded in the region 4000-100 cm(-1). The optimized geometries were calculated by HF and DFT (B3LYP) methods with 6-31++G (d, p), 6-311G (d, p) and 6-311++G (d, p) basis sets. The harmonic vibrational frequencies, infrared intensities and Raman activities of the 2,3-DMN were evaluated with these methods. After scaling the computational wave numbers are in very good agreement with the experimental values. A detailed interpretation of the infrared and Raman spectra of 2,3-DMN is presented. The effects of substitution of methyl group on the molecule have also been discussed.     

Density functional theory study of Fourier transform infrared and Raman spectra of 2-amino-5-chloro benzonitrile

The vibrational spectra of 2-amino-5-chloro benzonitrile (ACB) have been obtained by density functional theory (DFT) calculations. Normal coordinate analysis has been carried out to support the vibrational analysis. The results were compared with the experimental values. With the help of scaling procedures, the observed FTIR and FT Raman vibrational frequencies were analysed and compared with the theoretically predicted vibrational spectra. The assignments of bands to various normal modes of the molecules were also carried out.