Simulation of IR and Raman spectral based on scaled DFT force fields: a case study of 2-amino 4-hydroxy 6-trifluoromethylpyrimidine, with emphasis on band assignment

Experimental and theoretical investigations of spectroscopic properties of 8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine

The Fourier transform infrared (FTIR) and FT-Raman spectra of 8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine (8C1M6PB) have been recorded in the range of 4000-400 and 4000-100 cm(-1), respectively. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated potential energy distribution (PED). The equilibrium geometries, harmonic frequencies, infrared intensities and Raman scattering activities were calculated by Hartree-Fock (HF) and density functional B3LYP method with the 6-31G (d,p) basis set. The vibrational frequencies were calculated in all these methods and were compared with the experimental frequencies which yield good agreement between observed and calculated frequencies. The first order hyperpolarizability (βtotal) of this molecular system and related properties (β, μ, and Δα) are calculated using HF/6-31G (d,p) and B3LYP/6-31G(d,p) methods based on the finite-field approach. The calculated Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies show that charge transfer occurs in the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Conformation analysis was carried for 8C1M6PB by Potential energy surface scan to find all possible conformers with B3LYP method using 6-31G (d,p) basis set. The entropy of the title compound is also performed at HF/6-31G (d,p) and B3LYP/6-31G(d,p) levels of theory. In addition, the thermodynamic properties of the compound were calculated at different temperatures and corresponding relations between the properties and temperature were also studied.

Quantum mechanical study of the structure and vibrational spectroscopic (FT-IR and FT-Raman), first-order hyperpolarizability, NBO and HOMO-LUMO studies of 4-bromo-3-nitroanisole

The FT-IR and FT-Raman spectra of 4-bromo-3-nitroanisole (BNA) molecule have been recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1), respectively. Optimized geometrical structure, harmonic vibrational frequencies, intensities, reduced mass, force constants and depolarization ratio have been computed by ab initio HF and the B3LYP density functional levels using 6-311++G (d,p) basis set. The observed FT-IR and FT-Raman vibrational frequencies are analyzed 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 first-order hyperpolarizability (β) of the investigated molecule were computed using DFT calculations. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and analyzed. The influences of bromine atom, nitrile group and methyl group on the geometry of benzene and its normal modes of vibrations have also been discussed.

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.

Molecular structure, FT-IR, FT-Raman, NMR studies and first order molecular hyperpolarizabilities by the DFT method of mirtazapine and its comparison with mianserin

Mirtazapine (±)-1,2,3,4,10,14b-hexahydro-2-methylpyrazino(2,1-a)pyrido(2,3-c)(2)benzazepine is a compound with antidepressant therapeutic effects. It is the 6-aza derivative of the tetracyclic antidepressant mianserin (±)-2-methyl-1,2,3,4,10,14b-hexahydrodibenzo[c,f]pyrazino[1,2-a]azepine. The FT-IR and FT-Raman spectra of mirtazapine have been recorded in 4000-400 cm(-1) and 3500-10 cm(-1), respectively. The optimized geometry, energies, nonlinear optical properties, vibrational frequencies, (13)C, (1)H and (15)N NMR chemical shift values of mirtazapine have been determined using the density functional theory (DFT/B3LYP) method. A comparison of the experimental and theoretical results of mirtazapine indicates that the density-functional B3LYP method is able to provide satisfactory results for predicting vibrational and NMR properties. The experimental and calculated results for mirtazapine have also been compared with mianserin.

Molecular structures, FT-IR and FT-Raman spectra, NBO analysis, NLO properties, reactive sites and quantum chemical calculations of keto-enol tautomerism (2-amino-4-pyrimidinol and 2-amino-pyrimidine-4(1H)-one)

The keto-enol tautomerism of 2-amino-4-pyrimidinol (APN) and 2-amino-pyrimidine-4(1H)-one (APO) are investigated by vibrational spectroscopy and quantum chemical method. FT-IR and FT-Raman spectra are recorded in the regions of 4000-400 cm(-1) and 3500-100 cm(-1), respectively for APN. Geometrical parameters, vibrational wavenumbers of APN and APO are predicted by density functional theory (DFT) employing B3LYP level with 6-311++G(d,p) and 6-311++G(2d,p) basis sets. The non-linear optical (NLO) properties of the title molecules are computed. The molecular electrostatic potential (MEP) surface maps are plotted and explained in detail. Natural bond orbital (NBO) analyses have been performed on APN molecule. The significant changes in occupancies and the energies of bonding and antibonding orbital have been explained in detail. Thermodynamic properties (heat capacities, entropies, and enthalpy) and their correlations with temperatures are also obtained from the calculated frequencies of the optimized structures. Reactivity descriptors, Fukui functions and electrophilic sites are found and discussed.

Experimental (FT-IR and FT-Raman) and theoretical (HF and DFT) investigation, NMR, NBO, electronic properties and frequency estimation analyses on 2,4,5-trichlorobenzene sulfonyl chloride

The present work deals with the structural, electronic, and vibrational analyses of the biomolecule 2,4,5-trichlorobenzene sulfonyl chloride (TCBSC). TCBSC is a novel pharmaceutical compound used in dyes, pesticides, pigments, fluorescence brighteners and intermediate for agricultural chemicals in the manufacture of insecticides. Quantum chemical calculation of geometrical structure and energies of TCBSC was carried out by density functional theory (B3LYP) and ab initio (HF) methods at 6-311+G(d,p) and 6-311++G(d,p) standard basis set. The stability of the molecule arising from hyperconjugative interaction and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. NMR analysis shows that the isotropic chemical shifts of carbon and hydrogen atom of TCBSC are giving the reasonable shielding to the molecule. Another interesting property shows nonlinear optical (NLO) behavior. Moreover, we have not only simulated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) but also determined the transition state and energy band gap.

Quantum chemical studies on structure of 2-amino-5-nitropyrimidine

FTIR and FT Raman spectra of 2-amino-5-nitropyrimidine (2A5NP) are recorded in the region 4000-400 cm(-1) and 3500-0 cm(-1), respectively. Molecular structure and vibrational frequencies of 2A5NP have been investigated by density functional theory (DFT) calculations using Becke's three parameter exchange functional combined with Lee-Yang-Parr correlation (B3LYP) and Hartree fock (HF) method employing 6-311++G(d,p) basis set. Calculations have been performed giving energies, optimized structure, harmonic vibrational frequencies, IR intensities and Raman activities. Raman and IR spectra of 2A5NP were recorded and complete assignment of the observed vibrational bands of 2A5NP have been proposed. The predicted first hyperpolarizability suggests that the title compound is an attractive object for future studies of non-linear optical properties. The calculated HOMO-LUMO energies shows that charge transfer occur within the molecule and their related molecular properties were also discussed. The theoretical FT-IR and FT-Raman spectra for the title compound have also been constructed.

Vibrational spectroscopic, first-order hyperpolarizability and HOMO, LUMO studies of 4-chloro-2-(trifluoromethyl) aniline based on DFT calculations

The Fourier-transform infrared and FT-Raman spectra of 4-chloro-2-(trifluoromethyl) aniline (4C2TFA) were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 4C2TFA were carried out by density functional theory (DFT/B3LYP) method with 6-311+G(d,p) and 6-311++G(d,p) basis sets. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the total dipole moment (μ) and the first order hyperpolarizability (β) of the investigated compound were computed using B3LYP/6-311++G(d,p) calculations. The calculated results also show that 4C2TFA might have microscopic non-linear optical (NLO) behavior with non-zero values. A detailed interpretation of infrared and Raman spectra of 4C2TFA is also reported. The calculated HOMO-LUMO energy gap shows that charge transfer occurs within the molecule.

Vibrational spectroscopic investigation (FT-IR and FT-Raman) on 1,2-dibromobenzene by HF and hybrid (LSDA and B3LYP) calculations

The FT-IR and FT-Raman spectra of the compound 1,2-dibromobenzene have been recorded in the region 4000-100cm(-1). The vibrational analysis has been made using HF and DFT (B3LYP and LSDA) level of theory by employing 6-31 +G (d, p) and 6-311 ++G (d, p) basis sets. Optimized geometrical parameters have been calculated, interpreted and compared with the reported experimental values of some halogen-substituted benzene. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction of HF and DFT. The geometrical structure of the compound is fractured by the substitutions of couple of Br in the ring. From the vibrational assignments it is observed that, the vibrational pattern of the fundamental modes is realigned slightly with respect to the substitutions. The simulated FT-IR and FT-Raman spectra of the compound for different methods are compared with the experimental spectra. The impact of Br in the vibrational assignments of the molecule is also investigated.

Spectroscopic (FT-IR, FT-Raman and UV-vis) investigation and frontier molecular orbitals analysis on 3-methyl-2-nitrophenol using hybrid computational calculations

In the present study, the FT-IR and FT-Raman spectra of 3-methyl-2-nitrophenol (C(7)H(7)O(3)N) (3M2NP) have been recorded in the range of 4000-100 cm(-1). The fundamental modes of vibrational frequencies of 3M2NP are assigned. All the geometrical parameters have been calculated by HF and DFT (LSDA and B3LYP) methods with 6-31G(d,p) and 6-311G(d,p) basis sets. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for phenol and some substituted phenol. The harmonic and anharmonic vibrational wave numbers, IR intensities and Raman activities are calculated at the same theory levels used in geometry optimization. The calculated frequencies are scaled and compared with experimental values. The scaled vibrational frequencies at LSDA/B3LYP/6-311G(d,p) seem to coincide with the experimentally observed values with acceptable deviations. The impact of substitutions on the benzene structure is investigated. The molecular interactions between the substitutions (OH, CH(3) and NO(2)) are also analyzed. A detailed interpretation of the infrared spectra of was also reported more precisely. Charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap are calculated and presented. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated, revealing the correlations between standard heat capacities (C) standard entropies (S), and standard enthalpy changes (H) and temperatures.

Comparative vibrational analysis of 1,2-Dinitro benzene and 1-Fluoro-3-nitro benzene: a combined experimental (FT-IR and FT-Raman) and theoretical study (DFT/B3LYP/B3PW91)

In this work, the comparative analysis is made on the structure and vibrational spectra of 1,2-Dinitro benzene (1,2-DNB) and 1-Fluoro-3-nitro benzene (1-F-3-NB) molecules. The FT-IR and FT-Raman experimental spectra of the molecules have been recorded using Bruker IFS 66 V spectrometer in the range of 4000-100 cm(-1). Making use of the recorded data, the complete vibrational assignments are made and analyses of the observed fundamental bands of molecules are carried out. The experimental determinations of vibrational frequencies are compared with those obtained theoretically from ab-initio Hartree-fock (HF) and DFT (B3LYP and B3PW91) methods with 6-31++G (d, p) and 6-311++G (d, p) basis sets. The differences between the observed and scaled wave number values of most of the fundamentals of the molecules are very small in B3LYP than HF. The geometries and normal modes of vibrations obtained from ab-initio HF and B3LYP/B3PW91 calculations are compared with the experimentally observed data. Comparison of the simulated spectra of the molecules provides important information regarding the difference and similarity of the vibrational characteristics between the molecules. The impact of substitutions on the structures between the molecules is also investigated.

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.

FT-IR and FT-Raman, UV spectroscopic investigation of 1-bromo-3-fluorobenzene using DFT (B3LYP, B3PW91 and MPW91PW91) calculations

The FT-IR and FT-Raman spectra of 1-bromo-3-fluorobenzene (C(6)H(4)FBr) molecule have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1). The molecular geometry and vibrational frequencies in the ground state are calculated using the DFT (B3LYP, B3PW91 and MPW91PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. The isotropic DFT (B3LYP, B3PW91 and MPW1PW91) analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by B3LYP methods. The complete data of this molecule provide the information for future development of substituted benzene. The influence of bromine and fluorine atom on the geometry of benzene and its normal modes of vibrations has also been discussed. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, was performed by time dependent DFT (TD-DFT) approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds were 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 in gas phase, revealing the correlations between standard heat capacities (C) standard entropies (S), standard enthalpy changes (H) and temperatures.

MP2, DFT and ab initio calculations on thioxanthone

Density functional theory (DFT), HF and MP2 calculations have been carried out to investigate thioxanthone molecule using the standard 6-31+G(d,p) basis set. The results of MP2 calculations show a butterfly structure for thioxanthone. The calculated results show that the predicted geometry can well reproduce the structural parameters. The predicted vibrational frequencies were assigned and compared with experimental IR spectra. A good harmony between theory and experiment is found. The theoretical electronic absorption spectra have been calculated using CIS method. (13)C and (1)H NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31+G(d,p) basis set. The comparison of the experimental and the theoretical results indicate that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.

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.

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.

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.

FT-IR and FT-Raman, vibrational assignments, molecular geometry, ab initio (HF) and DFT (B3LYP) calculations for 1,3-dichlorobenzene

The FT-IR and FT-Raman vibrational spectra of 1,3-dichlorobenzene (1,3-DCB) have been recorded using Bruker IFS 66 V Spectrometer in the range 4000-100 cm(-1). 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 optimized molecular geometry, vibrational frequencies, atomic charges, dipole moment, rotational constants and several thermodynamic parameters in the ground state were calculated using ab initio Hartree-Fock (HF) and DFT (B3LYP) methods with 6-31++G (d, p) and 6-311++G (d, p) basis sets. With the help of different scaling factors, the observed vibrational wave numbers in FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wave numbers in the expected range. The inductive effect of Chlorine atoms in the benzene molecule has also been investigated.

Molecular Structure and Vibrational Analysis of 1-Bromo-2-Chlorobenzene Using ab initio HF and Density Functional Theory (B3LYP) Calculations

The FT-Raman and FT-IR spectra for 1-bromo-2-chlorobenzene (1B2CB) 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 6-31+G (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 benzene are affected upon profusely with the halogen substitutions in comparison to benzene, and these differences are interpreted.

Density functional theory calculation and vibrational spectroscopy study of 2-amino-4,6-dimethyl pyrimidine (ADMP)

The solid phase FTIR and FT-Raman spectra of 2-amino-4,6-dimethyl pyrimidine (ADMP) have been recorded in the regions 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The structure was investigated by utilizing density functional theory (DFT) calculations with the Becke 3-Lee-Yang-Parr (B3LYP) method employing the 6-31+G and 6-311++G basis sets. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental data. Complete vibrational assignments were made on the basis of normal coordinate analysis (NCA) for the molecule. The infrared and Raman spectra were also predicted from the calculated intensities. The observed and the calculated spectra were found to be in good agreement. The thermodynamic properties like entropies and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized structures.

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.

Vibrational spectroscopy [FTIR and FTRaman] investigation, computed vibrational frequency analysis and IR intensity and Raman activity peak resemblance analysis on 4-chloro 2-methylaniline using HF and DFT [LSDA, B3LYP and B3PW91] calculations

In the present study, the FT-IR and FT-Raman spectra of 4-chloro-2-methylaniline (4CH2MA) have been recorded in the range of 4000-100 cm(-1). The fundamental modes of vibrational frequencies of 4CH2MA are assigned. All the geometrical parameters have been calculated by HF and DFT (LSDA, B3LYP and B3PW91) methods with 6-31G (d, p) and 6-311G (d, p) basis sets. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for aniline and some substituted aniline. The harmonic and anharmonic vibrational wavenumbers, IR intensities and Raman activities are calculated at the same theory levels used in geometry optimization. The calculated frequencies are scaled and compared with experimental values. The scaled vibrational frequencies at LSDA/B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The impact of substitutions on the benzene structure is investigated. The molecular interactions between the substitutions (Cl, CH(3) and NH(2)) are also analyzed.

Vibrational spectroscopy (FTIR and FTRaman) investigation using ab initio (HF) and DFT (B3LYP) calculations on the structure of 3-Bromo phenol

The FT-IR and FT-Raman spectra of 3-Bromo phenol (3-BP) molecule have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1). The molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-fock (HF) and DFT (B3LYP) methods with 6-31G (d, p) and 6-311G (d, p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The geometries and normal modes of vibrations obtained from ab initio HF and B3LYP calculations are in good agreement with the experimentally observed data. The differences between the observed and scaled wave number values of most of the fundamentals are very small in DFT than HF. The inductive effect of halogen atom in the molecule has also been investigated.

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 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.

FT-IR and FT-Raman spectra and vibrational investigation of 4-chloro-2-fluoro toluene using ab initio HF and DFT (B3LYP/B3PW91) calculations

FT-IR (4000-100 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectra of solid sample of 4-chloro-2-fluoro toluene (4Cl2FT) have been recorded using Bruker IFS 66 V spectrometer. Ab initio-HF (HF/6-311++G (d, p)) and DFT (B3LYP/6-311++G and B3PW91/6-311++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. The isotropic HF and DFT analyses showed good agreement with experimental observations. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. Comparison of the simulated spectra provides important information about the ability of the computational method (B3LYP) to describe the vibrational modes. The influences of substitutions on the geometry of molecule and its normal modes of vibrations have also been discussed. The changes made by substitutions on the benzene are much responsible for the non-linearity of the molecule. This is an attractive entity for the future studies of non-linear optics.

Vibrational spectroscopic investigation and DFT studies on 2,2',4,4'-tetrabromodiphenyl ether

In the present work, the infrared (IR) and Raman spectra of 2,2',4,4'-tetrabromodiphenyl ether have been measured in the ranges of 400-4000cm(-1) and 100-4000cm(-1). The geometry optimized by the density functional theory Becke-3-Lee-Yang-Parr (B3LYP) method with the 6-31G(d) basis set was in good agreement with the experimental data of analogues. The results have shown that the dihedral angle of biphenyl ether significantly increases with the addition of bromine substitution. The vibrational frequencies were evaluated by the B3LYP method in conjunction with basis sets of 6-31G(d), 6-31G(2df,p), 6-311+G(d,p), 6-311G+(2df,p), and 6-311++G(d,p), separately. The scaled frequencies resulted in excellent agreement with the observed spectral patterns. The correlation analysis and statistical comparisons indicated that the basis sets larger than 6-31G(d) resulted in no significant improvement in the accuracy of the vibration frequencies. The detailed assignments were performed according to the calculated results for B3LYP/6-31G(d) and then compared with those from a previous study on 4,4'-dibromodiphenyl ether. The absence of coupling of C-O stretching and adjacent C-H in-plane deformation indicated a strong steric effect owing to the ortho bromine atoms in the title compound. Moreover, the quantum theory of atoms in molecules (QTAIM) and the Moller-Plesset second-order perturbation (MP2) method are applied to exclude the possible formation of intramolecular non-covalent interactions such as Br...Br and C-H...Br.

Vibrational spectroscopy (FTIR and FTRaman) investigation using ab initio (HF) and DFT (B3LYP and B3PW91) analysis on the structure of 2-amino pyridine

The FTIR and FTRaman spectra of 2-amino pyridine (2-AP) molecule have been recorded using Bruker IFS 66 V spectrometer in the range of 4000-100 cm(-1). The molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-Fock (HF) and DFT (B3LYP and B3PW91) methods with 6-31++G (d, p) and 6-311++G (d, p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The geometries and normal modes of vibrations obtained from ab initio HF and B3LYP/B3PW91 calculations are in good agreement with the experimentally observed data. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. The influence of N atom and amine group in the skeletal ring vibrations of the title molecule has also been discussed.

FTIR and FTRaman spectroscopic investigation of 2-bromo-4-methylaniline using ab initio HF and DFT calculations

The FTIR and FTRaman spectra of 2-bromo-4-methyl aniline (2-B-4-MA) molecule have been recorded using Brucker IFS 66V spectrometer in the range of 4000-100 cm(-1). The molecular geometry and vibrational frequencies in the ground state are calculated using the Hartree-Fock (HF) and B3LYP with 6-31+G*(d, p), 6-311+G*(d, p) and 6-311++G* (d, p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. The isotropic HF and DFT analysis showed good agreement with experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by HF and B3LYP methods indicates that B3LYP/6-311++G* (d, p) is superior to HF/6-31+G* for molecular vibrational problems. The complete data of this title compound provide the information for future development of substituted aniline. The influences of bromine atom, methyl group and amine group on the geometry of benzene and its normal modes of vibrations have also been discussed.

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 (C(6)H(6)N(2)O) are studied. FT-IR and FT-Raman spectra of title molecule in the liquid phase have been recorded in the region 4000-100cm(-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.

FTIR and FTRaman spectra, assignments, ab initio HF and DFT analysis of 4-nitrotoluene

In this work, the experimental and theoretical study on molecular structure and vibrational spectra of 4-nitrotoluene are studied. The FTIR and FTRaman experimental spectra of the molecule have been recorded in the range of 4000-100 cm(-1). Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The experimental determinations of vibrational frequencies are compared with those obtained theoretically from ab initio HF and DFT quantum mechanical calculations using HF/6-31G (d, p), B3LYP/6-31++G* (d, p) and B3LYP/6-311++G* (d, p) methods. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. The geometries and normal modes of vibrations obtained from ab initio HF and B3LYP calculations are in good agreement with the experimentally observed data. Comparison of the simulated spectra provides important information about the ability of the computational method (B3LYP) to describe the vibrational modes. The vibrations of NO(2) and CH(3) groups coupled with skeletal vibrations are also investigated.