FT-IR, FT-Raman spectra and ab initio HF, DFT vibrational analysis of 2,3-difluoro phenol

The FT-IR and FT-Raman spectra of 2,3-difluoro phenol (2,3-DFP) has been recorded in the region 4000-400 and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of 2,3-DFP were obtained by the ab initio HF and density functional theory (DFT) levels of theory with complete relaxation in the potential energy surface using 6-311+G(d,p) basis set. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR 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,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 50–3500 cm^?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). ¹³C and ¹H 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.     

Molecular structure and vibrational analysis of 3-Ethylpyridine using ab initio HF and density functional theory (B3LYP) calculations

The FT-Raman and FT-IR spectra for 3-Ethylpyridine (3-EP) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using HF/DFT (B3LYP) method by employing 6-31G(d,p) and 6-311++G(d,p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by HF and DFT (B3LYP) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values of some substituted benzene. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from HF and DFT. The scaled vibrational frequencies at B3LYP/6-311++G(d,p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the pyridine are effected upon profusely with the C2H5 substitutions in comparison to pyridine and these differences are interpreted.     

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.     

Spectroscopic investigation, computed IR intensity, Raman activity and vibrational frequency analysis on 3-bromoanisole using HF and DFT (LSDA/MPW1PW91) calculations

In this work, the experimental and theoretical spectra of 3-bromoanisole (3-BA) are studied. FT-IR and FT-Raman spectra of title molecule in the liquid phase 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 (LSDA and MPW1PW91) with the 6-31G (d, p) and 6-311G (d, p) basis sets. The vibrational frequencies are calculated and scaled values have been compared with the experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found in good agreement. The DFT-LSDA/6-311G (d, p) calculations have been found are more reliable than the ab initio HF/6-31G (d, p) calculations for the vibrational study of 3-BA. The optimized geometric parameters (bond lengths and bond angles) are compared with experimental values of the molecule. The alteration of vibrational bands due to the substitutions in the base molecule is also investigated from their characteristic region of linked spectrum.     

Molecular structure and vibrational investigation of benzenesulfonic acid methyl ester using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) theory calculations

The FT-Raman and FT-IR spectra for benzenesulfonic acid methyl ester (BSAME) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) method by employing 6-311G (d, p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for sulfonic acid and some substituted sulfonic acids. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from DFT. The scaled vibrational frequencies at LSDA/B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the sulfonic acid are effected upon profusely with the methyl substitution in comparison to benzene sulfonamide and these differences are interpreted.     

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra of 2,4-DCP and 4,6-DCP was reported on the basis of the calculated potential energy distribution (PED). A comparison of theoretically calculated vibrational frequencies at B3LYP/6-311++G(d,p) with FT-IR and FT-Raman experimental data shows good agreement between them. Natural atomic charges of 2,4-DCP and 4,6-DCP were calculated and compared with pyrimidine molecule.     

Molecular structure and vibrational spectra of phenobaraitone by density functional theory and ab initio hartree-Fock calculations

Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry, harmonic vibrational frequency along with intensities in IR and Raman spectra at RHF/6-31++G** and B3LYP/6-31++G** levels for phenobarbitone (C₁₂H₁₂N₂O₃) in the ground state. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR and FT-Raman spectra. Theoretical vibrational spectra of the title compound were interpreted by means of potential energy distributions (PEDs) using MOLVIB program. A detailed interpretation of the infrared spectra of the title compound is reported. On the basis of the agreement between the calculated and observed results, the assignments of fundamental vibrational modes of phenobarbitone were examined and some assignments were proposed. The theoretical spectrograms for FT-IR and FT-Raman spectra of the title compound have been constructed.     

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.     

FT-IR and FT-Raman vibrational spectra and molecular structure investigation of nicotinamide: A combined experimental and theoretical study

In this work, the experimental and theoretical spectra of nicotinamide (C₆H₆N₂O) are studied. FT-IR and FT-Raman spectra of title molecule in the liquid phase 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 6-31+G*(d, p) and 6-31++G* (d, p)basis set. The vibrational frequencies have been calculated and scaled values have been compared with the experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found in good agreement. The DFT-B3LYP/6-31++G (d, p) calculations have been found are more reliable than the ab initio HF/6-31+G (d, p) calculations for the vibrational study of nicotinamide. The optimized geometric parameters (bond lengths and bond angles) are compared with experimental values of the molecule. The alteration of vibrational bands due to the substitutions in the base molecule is also investigated from their characteristic region of linked spectrum.     

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 spectra and ab initio HF, DFT vibrational analysis of p-chlorobenzoic acid

The infrared, the Fourier transform infrared and Fourier transform Raman spectra of p-chlorobenzoic acid (p-CBA) has been recorded in the region 4000-600 cm(-1), 4000-400 cm(-1) and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of p-CBA were obtained by the ab initio HF and DFT (B3LYP) methods with complete relaxation in the potential energy surface using 6-311+G(d,p) basis set. The harmonic-vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR 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.     

Experimental, theoretical calculations of the vibrational spectra and conformational analysis of 2,4-di-tert-butylphenol

In the present work, we reported a combined experimental and theoretical study on conformational stability, molecular structure and vibrational spectra of 2,4-di-tert-butylphenol (2,4-DTBP). The FT-IR (400-4000cm(-1)) and FT-Raman spectra (50-3500cm(-1)) of 2,4-DTBP were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2,4-DTBP in the ground-state have been calculated by using the density functional BLYP/B3LYP methods. The energy calculated by time-dependent density functional theory (TD-DFT) result complements with the experimental findings. The calculated highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies show that charge transfer occurs within the molecule. Finally the calculation results were compared with measured infrared and Raman spectra of the title compound which showed good agreement with observed spectra.     

Vibrational spectroscopic studies and ab initio calculations of 5-methyl-2-(p-fluorophenyl)benzoxazole

FT-Raman and FT-IR spectra of 5-methyl-2-(p-fluorophenyl)benzoxazole were recorded and analysed. The vibrational frequencies of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values.     

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.     

Molecular structure and vibrational spectra of 1,3-bis(4-pyridyl)propane by quantum chemical calculations

The experimental and theoretical study on the structures and vibrations of 1,3-bis(4-pyridyl)propane are presented. The FT-IR and Raman spectra of molecule have been measured. The optimized geometric bond lengths have been obtained by DFT show the best agreements with experimental values. The harmonic vibrational frequencies were calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. Majority of the computed wavenumbers were found to be in good agreement with experimental observations. A complete assignment of the fundamentals was proposed based on the total energy distribution (TED) calculation.     

FT-IR, FT-Raman vibrational spectra and molecular structure investigation of 2-chloro-4-methylaniline: A combined experimental and theoretical study

In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C₇H₈NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been 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 have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR 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 DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.     

Vibrational spectroscopic (FT-IR and FT-Raman), first-order hyperpolarizablity, HOMO, LUMO, NBO, Mulliken charges and structure determination of 2-bromo-4-chlorotoluene

The FT-IR and FT-Raman spectra of 2-bromo-4-chlorotoluene (2B4CT) molecule have been recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. Optimized geometrical structures, harmonic vibrational frequencies, intensities, reduced mass, force constants and depolarization ratio have been computed by the B3 based (B3LYP) density functional methods using 6-31+G(d,p) and 6-311++G(d,p) basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analysed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The Mulliken charges, the natural bonding orbital (NBO) analysis, the values of electric dipole moment (μ) and the first-order hyperpolarizability (β) of the investigated molecule were computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The influences of bromine atom, chlorine atom and methyl group on the geometry of benzene and its normal modes of vibrations have also been discussed.     

Molecular structure, vibrational, UV and NBO analysis of 4-chloro-7-nitrobenzofurazan by DFT calculations

In the present work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of 4-chloro-7-nitrobenzofurazan (NBD-Chloride). The FT-IR (400-4000 cm(-1)) and FT-Raman spectra (50-4000 cm(-1)) of NBD-Chloride were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of NBD-Chloride in the ground-state have been calculated by using the density functional B3LYP method with 6-311++G (d, p) as higher basis set. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) result in DMSO and CDCl3 solvents complements with each other. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Finally the calculation results were applied to simulate infrared and Raman spectra of the title compound which show good agreement with observed spectra.     

Experimental and theoretical investigation of the molecular and electronic structure of anticancer drug camptothecin

The Fourier Transform Infrared spectrum of (S)-4 ethyl-4-hydroxy-1H-pyrano [3',4':6,7]-indolizino-[1,2-b-quinoline-3,14-(4H,12H)-dione] [camptothecin] was recorded in the region 4000-400 cm(-1). The Fourier Transform Raman spectrum of camptothecin (CPT) was also recorded in the region 3500-50 cm(-1). Quantum chemical calculations of geometrical structural parameters and vibrational frequencies of CPT were carried out by MP2/6-31G(d,p) and density functional theory DFT/B3LYP/6-311++G(d,p) methods. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR and FT-Raman spectra. Most of the computed frequencies were found to be in good agreement with the experimental observations. The isotropic chemical shifts computed by (13)C and (1)H NMR analysis also show good agreement with experimental observations. Comparison of calculated spectra with the experimental spectra provides important information about the ability of computational method to describe the vibrational modes of large sized organic molecule.