Theoretical study on the geometry and vibration of 1-[6-(4-Chlorophenyl)-1-[(6-chloropyridin-3-yl)methyl]-2-[(6-chloropyridin-3-yl)methylsulfanyl]-4-methyl-1,6-dihydropyrimidin-5-yl]ethanone

The solid phase FT-IR and FT-Raman spectra of 1-[6-(4-chlorophenyl)-1-[(6-chloropyridin-3-yl)methyl]-2-[(6-chloropyridin-3-yl)methylsulfanyl]-4-methyl-1,6-dihydropyrimidin-5-yl]ethanone (C25H21Cl3N4OS) were recorded in the region 4000-400 and 3500-100cm(-1), respectively. The vibrational spectra have been computed using density functional theory (B3LYP) and ab initio molecular orbital calculation (HF) with 6-31G(d, p) basis sets. A close agreement was achieved between the observed and calculated frequency by employing normal coordinate calculations. The observed and simulated spectra were found to be well comparable.     

Scaled quantum chemical calculations and FT-IR, FT-Raman spectral analysis of 2-methyl piperazine

The vibrational spectra of 2-methyl piperazine (2MPZ) have been computed using B3LYP methodology and 6-31G* and 6-31G** basis sets. The solid phase FT-IR 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 employing normal coordinate calculations. The observed and simulated spectra were found to be well comparable.     

FTIR, FT-Raman spectra and ab initio DFT vibrational analysis of 2,4-dichloro-6-nitrophenol

The FTIR and FT-Raman spectra of 2,4-dichloro-6-nitrophenol (2,4-DC6NP) has been recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of (2,4-DC6NP) were obtained by the ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311+G(d,p) basis sets. 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 experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.     

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.     

Scaled quantum chemical calculations and FTIR, FT-Raman spectral analysis of 3,4-diamino benzophenone

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.     

Density functional theory studies on tautomeric stability and infrared and Raman spectra of some purine derivatives

The molecular vibrations of 6-hydroxy-purine (6HP) and 6-amino-purine (6AP) were investigated in polycrystalline sample, at room temperature by Fourier transform infrared (FTIR) and FT-Raman spectroscopy. The spectra of the above compounds have been recorded in the region 4000-50, 3500-100 cm(-1), respectively. They were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on density functional theory (DFT) using HF/6-31G* and B3LYP/6-311+G** methods and basis set combinations. The results of the calculations were applied to simulated infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The dipole moment and the tautometric stability of purine derivatives were also studied.     

Vibrational spectra and potential energy distributions for 4,5-dichloro-3-hydroxypyridazine by density functional theory and normal coordinate calculations

The solid phase FT-IR and FT-Raman spectra of 4,5-dichloro-3-hydroxypyridazine have been recorded in the regions 4000-400 cm(-1) 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* and B3LYP/6-311+G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. The IR and Raman spectra were predicted theoretically and compared with the experimental spectra.     

Density functional theory calculations and vibrational spectra of 3,5-dibromopyridine and 3,5-dichloro-2,4,6-trifluoropyridine

The solid phase mid FTIR and FT-Raman spectra of 3,5-dibromopyridine (3,5-DBP) and 3,5-dichloro-2,4,6-trifluoropyridine (3,5-DCTFP) have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The spectra were interpreted with the help of normal coordinate analysis (NCA) following full structure optimisation and force field calculations based on the density functional theory (DFT) using the standard B3LYP/6-31G( *) method and basis set combination. The results of the calculations are applied to stimulate infrared and Raman spectra of the title compounds which showed excellent agreement with the observed spectra.     

Structures and vibrational frequencies of 2-hydroxy-3-methoxy-5-nitrobenzaldehyde and 2-methoxy-1-naphthaldehyde based on density functional theory calculations

FT-IR and FT-Raman spectra of 2-hydroxy-3-methoxy-5-nitrobenzaldehyde (HMN) and 2-methoxy-1-naphthaldehyde (MN) have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The molecular structure, conformational stability, geometry optimization, vibrational frequencies have been investigated. The total energy calculations of HMN and MN were tried for various possible conformers. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using B3LYP/6-31G* and B3LYP/6-311+G** level and basis set combinations and was scaled using various scale factors yielding good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.     

Density functional study and the vibrational spectra of 4-chloro-5-fluoro-1,2-phenylenediamine

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.     

Density functional and experimental studies on the FT-IR and FT-Raman spectra and structure of 2,6-diamino purine and 6-methoxy purine

FT-IR and FT-Raman spectra of 2,6-diamino purine (DAP) and 6-methoxy purine (MP) have been recorded in the regions of 4000-400cm(-1) and 3500-100cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimizations and force field calculations based on density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G** method and basis set combinations. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies.     

Analysis of vibrational spectra of 5,6-dimethyl benzimidazole based on density functional theory calculations

The vibrational spectra of 5,6-dimethyl benzimidazole (5,6DBZ) have been computed using the standard B3LYP/6-311G** method and basis set combinations. The solid phase FT-IR 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 employing normal coordinate calculations. The observed and simulated spectra were found to be well comparable.     

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 spectroscopy investigation using ab initio and density functional theory analysis on the structure of 2-amino-4,6-dimethoxypyrimidine

The FTIR and FT-Raman spectra of 2-amino-4,6-dimethoxypyrimidine (2A46DMP) has been recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of 2A46DMP were obtained by the ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311G(d,p) basis sets. 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 experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.     

FT-IR and FT-Raman spectroscopic investigation, computed vibrational frequency analysis and IR intensity and Raman activity peak resemblance analysis on 2-nitroanisole using HF and DFT (B3LYP and B3PW91) calculations

Fourier-transform Raman and infrared spectra of 2-nitroanisole are recorded (4000-100 cm(-1)) and interpreted by comparison with respective theoretical spectra calculated using HF and DFT method. The geometrical parameters with C(S) symmetry, harmonic vibrational frequencies, infrared and Raman scattering intensities are determined using HF/6-311++G (d, p), B3LYP/6-311+G (d, p), B3LYP/6-311++G (d, p) and B3PW91/6-311++G (d, p) level of theories. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The SQM method, which implies multiple scaling of the DFT force fields has been shown superior to the uniform scaling approach. The vibrational frequencies and the infrared intensities of the C-H modes involved in back-donation and conjugation are also investigated.     

Density functional theory study of vibrational spectra, and assignment of fundamental vibrational modes of 1-bromo 4-fluoronaphthalene

The FTIR and FT-Raman spectra of 1-bromo 4-fluoronaphthalene have been recorded in the regions 4000-100cm(-1) and 3500-100cm(-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.     

FTIR, FT-Raman spectra and ab initio DFT vibrational analysis of 2-amino-5-chloropyridine

The FTIR and FT-Raman spectra of 2-amino-5-chloropyridine (ACP) has been recorded in the region 4000-400 and 3500-100 cm-1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of ACP were obtained by the ab initio and density functional theory (DFT) levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311+G(2df,2p) basis sets. 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 experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.     

FT-IR and FT-Raman spectral investigation, computed IR intensity and Raman activity analysis and frequency estimation analysis on 4-chloro-2-bromoacetophenone using HF and DFT calculations

In this work, the experimental and theoretical spectra of 4-chloro-2-bromoacetophenone (4C2BAP) are studied. FT-IR and FT-Raman spectra of title molecule have been recorded in the region 4000-100 cm(-1). The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock and density functional method (B3LYP) with the 6-31G (d, p) and 6-311G (d, p) basis sets. The vibrational frequencies are calculated and scaled values are compared with the experimental FT-IR and FT-Raman spectra. The DFT (B3LYP/6-311G (d, p)) calculations are more reliable than the ab initio HF/6-311G (d, p) calculations for the vibrational study of 4C2BAP. The optimized geometric parameters (bond lengths and bond angles) are compared with experimental values of the molecule. The alteration of vibrational bands of the carbonyl and acetyl groups due to the presence of halogens (Cl and Br) in the base molecule is also investigated from their characteristic region of linked spectrum.     

Experimental (FT-IR and FT-Raman) and theoretical (HF and DFT) investigation, IR intensity, Raman activity and frequency estimation analyses on 1-bromo-4-chlorobenzene

The FT-IR and FT-Raman spectra of 1-bromo-4-chlorobenzene (1-Br-4-CB) have been recorded using Bruker IFS 66V spectrometer in the region of 4000-100 cm(-1). Ab-initio-HF (HF/6-311+G (d, p)) and DFT (B3LYP/6-31++G (d, p)/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. Comparison of simulated spectra with the experimental spectra provides important information, the computational method have the ability to describe the vibrational methods. The frequency estimation analysis on HF and DFT is made. The impact of di-substituted halogens on the benzene molecule has also been discussed.