FT-IR, FT-Raman spectra and ab initio HF and DFT calculations of 4-N,N'-dimethylamino pyridine

Trace detection of tetrabromobisphenol A by SERS with DMAP-modified magnetic gold nanoclusters

Magnetic gold nanoclusters (MGNCs) functionalized with 4-dimethylaminopyridine (DMAP) enables the trace detection of tetrabromobisphenol A (TBBPA), an environmental pollutant, using surface-enhanced Raman scattering (SERS) spectroscopy. The synthesis, cleansing, and functionalization of MGNCs are conducted in aqueous solutions; SERS samples are prepared by magnetic precipitation in the presence of trace analyte. The limit of detection (LOD) for TBBPA is greatly increased by the use of DMAP as a reporter molecule: DMAP-modified MGNCs can detect TBBPA at 10 pM in water, whereas the LOD for TBBPA by unfunctionalized Au is 1 nM. The reproducibility of picomolar TBBPA detection with DMAP-modified MGNCs is confirmed by two-dimensional correlation analysis. The high SERS sensitivity for TBBPA can be attributed to its capacity to modulate the Raman spectrum of adsorbed DMAP. This indirect mode of detection can also be applied toward the detection of other hydrophobic analytes, each identifiable by its characteristic SERS identity.

Halochromism, ionochromism, solvatochromism and density functional study of a synthesized copper(II) complex containing hemilabile amide derivative ligand

This study investigates chromotropism of newly synthesized 3,3'-(ethane-1,2-diylbis(benzylazanediyl))dipropanamide copper(II) perchlorate complex. The compound was structurally characterized by physico-chemical and spectroscopic methods. X-ray crystallography of the complex showed that the copper atom achieved a distorted square pyramidal environment through coordination of two amine N atoms and two O atoms of the amide moieties. The pH effect on the visible absorption spectrum of the complex was studied which functions as pH-induced "off-on-off" switches through protonation and deprotonation of amide moieties along with the CuO to CuN bond rearrangement at room temperature. The complex was also observed to show solvatochromism and ionochromism. The distinct solution color changes mainly associated with hemilability of the amide groups. The solvatochromism of the complex was investigated with different solvent parameter models using stepwise multiple linear regression method. The results suggested that the basicity power of the solvent has a dominant contribution to the shift of the d-d absorption band of the complex. Density functional theory, DFT calculations were performed in order to study the electronic structure of the complex, the relative stabilities of the CuN/CuO isomers, and to understand the nature of the halochromism processes taking place. DFT computational results buttressed the experimental observations indicating that in the natural pH (5.8) the CuO isomer is more stable than its linkage isomer and conversely in alkaline aqueous solution.

Synthesis, structural characterization and theoretical approach of 3-(2,6-dichlorobenzyl)-5-methyl-N-nitro-1,3,5-oxadiazinan-4-imine

3-(2,6-Dichlorobenzyl)-5-methyl-N-nitro-1,3,5-oxadiazinan-4-imine (DNOI) was synthesized and characterized by X-ray diffraction, FT-IR, FT-Raman and UV-Vis spectra. The X-ray diffraction study showed that DNOI has a one dimensional configuration, due to the intermolecular C9H⋯O1 and N4H⋯O2 hydrogen bonds. The benzene ring and the oxadiazine rings are tilted with respect to each other by 63.07° (C3N1C5C6). Vibrational spectra and electronic spectra measurements were made for the compound. Optimized geometrical structure and harmonic vibrational frequencies were computed with DFT (B3LYP, B3P86, and M062X) methods using 6-311++G(d,p) basis set. Assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in CH3OH solution using TD-B3LYP/6-311++G(d,p) and PCM-B3LYP/6-311++G(d,p) approaches, respectively. The calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum. Temperature dependence of thermodynamic parameters in the range of 100-1000K were determined, entropy, heat capacity and enthalpy changes were increasing with temperature increasing, while for Gibbs free energy is decreasing with temperature increasing. The bond orbital occupancies, contribution from parent natural bond orbital (NBO), the natural atomic hybrids was calculated and discussed.

Investigation of structure, vibrational, electronic, NBO and NMR analyses of 2-chloro-4-nitropyridine (CNP), 2-chloro-4-methyl-5-nitropyridine (CMNP) and 3-amino-2-chloro-4-methylpyridine (ACMP) by experimental and theoretical approach

This study reports about the optimized molecular structures, vibrational wavenumbers, atomic charges, molecular electrostatic potentials, NBO, electronic properties, (1)H NMR and (13)C NMR chemical shifts for the molecules 2-chloro-4-nitropyridine (CNP), 2-chloro-4-methyl-5-nitropyridine (CMNP) and 3-amino-2-chloro-4-methylpyridine (ACMP). Theoretical calculations were performed by density functional theory (DFT)/B3LYP method using 6-311++G (d,p) basis set. The stability and charge delocalization of the title molecules were studied by natural bond orbital (NBO) analysis. Molecular electrostatic potential maps (MEP) were calculated to predict the reactive sites. The reactivity of the title compounds were investigated by HOMO-LUMO energies and global descriptors. The electronic properties of the compounds were also discussed and the transitions were found to be π→π(∗). In addition, the thermodynamic properties were studied for the title compounds and corresponding relations between the properties and temperature were also discussed. The hyperpolarizability values (βtot) were calculated for the title compounds. Hyperpolarizability value (βtot) of CMNP was found to be high and nineteen times greater than that of urea.

Molecular structure, spectroscopic (FTIR, FT-Raman, 13C and 1H NMR, UV), polarizability and first-order hyperpolarizability, HOMO-LUMO analysis of 2,4-difluoroacetophenone

The FTIR and FT-Raman spectra of 2,4-difluoroacetophenone (DFAP) have been recorded in the regions 4000-400 cm(-1) and 3500-50 cm(-1), respectively. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. The optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, were calculated by density functional theory (DFT/B3LYP) method with 6-31+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. A detailed interpretation of the infrared and Raman spectra of DFAP is also reported based on total energy distribution (TED). Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The MEP map shows the negative potential sites are on oxygen atom as well as the positive potential sites are around the hydrogen atoms. The UV-Vis spectral analysis of DFAP has also been done which confirms the charge transfer of DFAP. The chemical shifts of H atoms and C atoms were calculated using NMR analysis. Furthermore, the polarizability, the first hyperpolarizability and total dipole moment of the molecule have been calculated.

Spectroscopic and quantum chemical analysis of Isonicotinic acid methyl ester

In this present study, an organic compound Isonicotinic acid methyl ester (INAME) was structurally characterized by FTIR, FT-Raman, and NMR and UV spectroscopy. The optimized geometrical parameters and energies of all different and possible conformers of INAME are obtained from Density Functional Theory (DFT) by B3LYP/6-311++G(d,p) method. There are three conformers (SI, SII-1, and SII-2) for this molecule (ground state). The most stable conformer of INAME is SI conformer. The molecular geometry and vibrational frequencies of INAME in the ground state have been calculated by using HF and density functional method (B3LYP) 6-311++G (d,p) basis set. 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 computed vibrational frequencies were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. A study on the electronic properties, such as HOMO and LUMO energies were performed by time independent DFT approach. Besides, molecular electrostatic potential (MEP) and thermodynamic properties were performed. The electric dipole moment (μ) and first hyper polarizability (β) values of the investigated molecule were computed using ab initio quantum mechanical calculations. The calculated results show that the INAME molecule may have microscopic nonlinear optical (NLO) behavior with non zero values. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by gauge independent atomic orbital (GIAO) method.

Normal coordinate analysis, molecular structure, vibrational, electronic spectra and NMR investigation of 4-Amino-3-phenyl-1H-1,2,4-triazole-5(4H)-thione by ab initio HF and DFT method

In the present work, the characterization of 4-Amino-3-phenyl-1H-1,2,4-triazole-5(4H)-thione (APTT) molecule was carried out by quantum chemical method and vibrational spectral techniques. The FT-IR (4000-400 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectra of APTT were recorded in solid phase. The UV-Vis absorption spectrum of the APTT was recorded in the range of 200-400 nm. The molecular geometry, harmonic vibrational frequencies and bonding features of APTT in the ground state have been calculated by HF and DFT methods using 6-311++G(d,p) basis set. The complete vibrational frequency assignments were made by normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). The molecular stability and bond strength were investigated by applying the natural bond orbital analysis (NBO) and natural localized molecular orbital (NLMO) analysis. The electronic properties, such as excitation energies, absorption wavelength, HOMO and LUMO energies were performed by time depended DFT (TD-DFT) approach. The (1)H and (13)C nuclear magnetic resonance chemical shift of the molecule were calculated using the gauge-including atomic orbital (GIAO) method and compared with experimental results. Finally, the calculation results were analyzed to simulate infrared, FT-Raman and UV spectra of the title compound which shows better agreement with observed spectra.

Vibrational spectra, molecular structure, NBO, NMR, UV, first order hyperpolarizability, analysis of (S)-(-)-N-(5-Nitro-2-pyridyl) alaninol by Density functional theory

In this study, geometrical optimization, spectroscopic analysis, electronic structure and nuclear magnetic resonance studies of (S)-(-)-N-(5-Nitro-2-pyridyl) alaninol (abbreviated as SN5N2PLA) were investigated by utilizing HF and DFT/B3LYP with 6-31G(d,p) as basis set. The Fourier transform infrared (FT-IR) and FT-Raman spectra of SN5N2PLA were recorded in the region 4000-400cm(-1) and 3500-50cm(-1), respectively. Complete vibrational assignments, analysis and correlation of the fundamental modes for the title compound were carried out. UV-Visible spectrum of the compound that dissolved in methanol were recorded in the region 200-800nm and the electronic properties HOMO and LUMO energies were measured by TD-DFT approach. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The molecular stability and bond strength have been investigated by applying the Natural Bond Orbital (NBO) analysis. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of SN5N2PLA were calculated using the GIAO method in methanol solution and compared with the measured experimental data. The dipole moment, polarizability and first order hyperpolarizability values were also computed. The polarizability and first hyperpolarizability of the studied molecule indicate that the compound is a good candidate of nonlinear optical materials. The Chemical reactivity and Thermodynamic properties of SN5N2PLA at different temperature are calculated. In addition, molecular electrostatic potential (MEP), frontier molecular orbitals (FMOs) analysis were investigated using theoretical calculations.

Vibrational spectra, molecular structure, NBO, UV, NMR, first order hyperpolarizability, analysis of 4-Methoxy-4'-Nitrobiphenyl by density functional theory

In this study, geometrical optimization, spectroscopic analysis, electronic structure and nuclear magnetic resonance studies of 4-Methoxy-4'-Nitrobiphenyl (abbreviated as 4M4'NBPL) were investigated by utilizing HF and DFT/B3LYP with 6-31G(d,p) as basis set. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the 4M4'NBPL have been calculated with the help of density functional theory computations. The FT-IR and FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. Natural Bond Orbital (NBO) analysis is also used to explain the molecular stability. The UV-Vis absorption spectra of the title compound dissolved in chloroform were recorded in the range of 200-800 cm(-1). The HOMO-LUMO energy gap explains the charge interaction taking place within the molecule. Good correlation between the experimental (1)H and (13)C NMR chemical shifts in chloroform solution and calculated GIAO shielding tensors were found. The dipole moment, linear polarizability and first order hyperpolarizability values were also computed. The linear polarizability and first order hyperpolarizability of the studied molecule indicate that the compound is a good candidate of nonlinear optical materials. The chemical reactivity and thermodynamic properties of 4M4'NBPL at different temperature are calculated. In addition, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations.

Experimental and DFT studies on the vibrational, electronic spectra and NBO analysis of thiamethoxam

Vibrational and electronic spectral measurements were performed for 3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro) amine (thiamethoxam). Optimized geometrical structure and harmonic vibrational frequencies were calculated with ab initio RHF and DFT (B3LYP, CAMB3LYP, M06 and PBE1PBE) methods with 6-311++G (d, p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed in gas-phase using TD-B3LYP/6-311++G (d, p) approach and H2O solution using PCM-TD-B3LYP/6-311++G (d, p) approach. The calculated results matched well with the experimental values. Temperature dependence of thermodynamic parameters in the range of 100-1000 K were determined. The bond orbital occupancies, contribution from parent natural bond orbital (NBO), the natural atomic hybrids was discussed.

The spectroscopic (FT-IR, FT-Raman, UV and NMR) first order hyperpolarizability and HOMO-LUMO analysis of dansyl chloride

The solid phase FT-IR and FT-Raman spectra of dansyl chloride (DC) have been recorded in the regions 400-4000 and 50-4000 cm(-1), respectively. The spectra have been interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule has been optimized and the structural characteristics have been determined by density functional theory (B3LYP) method with 6-311++G(d,p) as basis set. The vibrational frequencies were calculated for most stable conformer and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra have also been predicted from the calculated intensities. (1)H and (13)CNMR spectra were recorded and (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-Visible spectrum of the compound was recorded in the region 200-600 nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Nonlinear optical and thermodynamic properties were interpreted. All the calculated results were compared with the available experimental data of the title molecule.

Molecular orbital studies (hardness, chemical potential and electrophilicity), vibrational investigation and theoretical NBO analysis of 4-4'-(1H-1,2,4-triazol-1-yl methylene) dibenzonitrile based on abinitio and DFT methods

The Fourier transform infrared (FTIR) and FT Raman (FTR) of 4-4'-(1H-1, 2, 4-triazol-1-yl methylene) dibenzonitrile (4-HTMDBN) have been recorded and analyzed. The equilibrium geometry harmonic vibrational frequencies have been investigated with the help of standard HF and DFT methods with 6-31G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). Theoretical simulations of the FTIR and FTR spectra of the title compound have been calculated. The (1)H and (13)C Nuclear Magnetic Resonance (NMR) chemical shifts of the molecule were calculated by the Gauge including atomic orbital (GIAO) method. The stability of the molecule has been analyzed using natural bond orbital (NBO) analysis. The linear polarizability (α) and the first order hyperpolarizability (β) values of the investigated molecule have been computed using HF/DFT/6-31G(d,p) methods on the finite field approach. UV-Vis spectrum of the compound is recorded and the electronic properties such as HOMO and LUMO energies, are performed. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), electrophilicity index (ω), hardness (η) and chemical potential (ρ) are all correlated with the HOMO and LUMO energies with their molecular properties. Mulliken population analysis on atomic charges, molecular electrostatic potential maps (MEP) and thermodynamical properties of title compound at different temperature have been calculated.

Experimental and DFT studies on the vibrational and electronic spectra and NBO analysis of 2-amino-3-((E)-(9-p-tolyl-9H-carbazol-3-yl) methyleneamino) maleonitrile

2-Amino-3-((E)-(9-p-tolyl-9H-carbazol-3-yl) methyleneamino) maleonitrile (ACMM) was synthesized and characterized by X-ray diffraction, FT-IR, FT-Raman and UV-Vis spectra. The X-ray diffraction study showed that ACMM has a Z-configuration, due to the intramolecular C18H18A⋯N2, N3H3A⋯N2 and C20H20A⋯N4 hydrogen bonds and intermolecular C10H10A⋯N4, N3H3B⋯N9 (2-x, 2-y, 2-z) and N3H8C⋯N4 (2-x, 1-y, 2-z) hydrogen bonds. The benzene ring including methyl is twisted from the mean plane of the carbazole group by 59.7(3)°. Vibrational spectra and electronic spectra measurements were made for the compound. Optimized geometrical structure and harmonic vibrational frequencies were computed with DFT (B3-based B3P86, B3LYP, B3PW91 and B-based BP86, BLYP, BPW91) methods and ab initio RHF method using 6-311++G(d, p) basis set. Assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in DMF solution using TD-B3LYP/6-311++G(d, p) and PCM-B3LYP/6-311++G(d, p) approaches, respectively. The calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum. Temperature dependence of thermodynamic parameters in the range of 100-1000K were determined. The bond orbital occupancies, contribution from parent natural bond orbital (NBO), the natural atomic hybrids was calculated and discussed.

Molecular structure, vibrational spectra, NLO and MEP analysis of bis[2-hydroxy-кO-N-(2-pyridyl)-1-naphthaldiminato-кN]zinc(II)

The molecular geometry and vibrational frequencies of bis[2-hydroxy-кO-N-(2-pyridyl)-1-naphthaldiminato-кN]zinc(II) in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-311G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The energetic and atomic charge behavior of the title compound in solvent media has been examined by applying the Onsager and the polarizable continuum model. To investigate second order nonlinear optical properties of the title compound, the electric dipole (μ), linear polarizability (α) and first-order hyperpolarizability (β) were computed using the density functional B3LYP and CAM-B3LYP methods with the 6-31+G(d) basis set. According to our calculations, the title compound exhibits nonzero (β) value revealing second order NLO behavior. In addition, DFT calculations of the title compound, molecular electrostatic potential (MEP), frontier molecular orbitals, and thermodynamic properties were performed at B3LYP/6-311G(d,p) level of theory.

On the spectroscopic analyses of thioindigo dye

A combined experimental and theoretical study on molecular structure and vibrational frequencies of thioindigo was reported. The FT-IR spectrum of thioindigo is recorded in the solid phase. The equilibrium geometries, harmonic vibrational frequencies, thermo-chemical parameters, total dipole moment and HOMO-LUMO energies are calculated by density functional theory DFT/B3LYP utilizing 6-311G(d,p) basis set. Results showed that cis-isomer is highly recommended to be a promising structure for many applications in optoelectronic devices due to its high calculated dipole moment value (3.44 Debye) which indicates its high reactivity to interact with the surrounding molecules as compared to the trans-isomer which has no dipole moment. Both isomers have a similar HOMO-LUMO energy gap, of 3.02 eV (cis-isomer) and 2.78 eV (trans-isomer).

FT-IR spectroscopic analyses of 4-hydroxy-1-methyl-3-[2-nitro-2-oxoacetyl-2(1H)quinolinone (HMNOQ)

In the present work, a combined experimental and theoretical study on molecular structure and vibrational frequencies of 4-hydroxy-1-methyl-3-[2-nitro-2-oxoacetyl-2(1H)quinolinone (HMNOQ) was reported. The FT-IR spectrum of HMNCQ is recorded in the solid phase. The equilibrium geometries, harmonic vibrational frequencies, thermo-chemical parameters, total dipole moment and HOMO-LUMO energies are calculated by density functional theory DFT/B3LYP utilizing 6-311G(d,p) basis set. Results showed that HMNOQ is highly recommended to be a promising structure for many applications in optoelectronic devices due to its high calculated dipole moment value (9 Debye) which indicates its high reactivity to interact with the surrounding molecules. The HOMO-LUMO energy gap of HMNOQ is 4 eV.

DFT approach for FT-IR spectra and HOMO-LUMO energy gap for N-(p-dimethylaminobenzylidene)-p-nitroaniline (DBN)

In the present work, a combined experimental and computational study for the optimized molecular structural parameters, FT-IR spectra, thermo-chemical parameters, total dipole moment and HOMO-LUMO energy gap for N-(p-diethylaminobenzylidene)p-nitroaniline (DBN) have been investigated using B3LYP/6-311G basis set. Our calculated results have showed that the investigated compound possesses a dipole moment of 12 Debye and HOMO-LUMO energy gap of 2.94 eV which indicate high recommendations for photovoltaic devices fabrication.

FT-IR spectroscopic analyses of 3-Methyl-5-Pyrazolone (MP)

In the present work both experimental and computational FT-IR spectroscopic studies on 3-Methyl-5-Pyrazolone (MP) were reported. Experimental FT-IR spectrum for MP compound is recorded in powder form. Important physical parameters were reported such as structural parameters, vibrational frequencies, entropy, total energy, total dipole moment and HOMO-LUMO energy gap using DFT/B3LYP/6-311G(d,p) basis set. MP molecule has a total dipole moment of 2.83 Debye and HOMO-LUMO energy gap of 5.80 eV. Results indicate also that exposure to UV changes the spin from singlet to doublet state; one can conclude that MP compound may undergo anomalous Zeeman like effect.

The molecular structure and vibrational spectra of N-(3-tert-butyl-2-hydroxybenzylidene)-2,6-diphenyl-4-hydroxyaniline

The molecular structure, vibrational frequencies and intensities of N-(3-tert-butyl-2-hydroxybenzylidene)-2,6-diphenyl-4-hydroxyaniline were calculated by the Density Functional Theory methods (BLYP, B3PW91 and B3LYP) using the 6-31G(d,p) basis set. The calculated geometric parameters were compared to the corresponding X-ray structure of the title compound. The comparison of the theoretical and experimental geometry of the title compound shows that the X-ray parameters fairly well reproduce the geometry of optimized by B3LYP method (r=0.9825). The harmonic vibrations computed for this compound by the B3LYP/6-31G(d,p) method are in good agreement with the observed IR and Raman spectral data. The root mean square values error of the observed and calculated IR bands are found to be 9.80, 9.40 and 8.42 for B3LYP, B3PW91 and BLYP/6-31G(d,p) methods, respectively. Theoretical vibrational spectra of the title compound were interpreted by means of PEDs using the SQM 2.0 program. A general better performance of the investigated methods was calculated by PAVF 1.0 program.

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.

Molecular structure, vibrational, UV, NMR, hyperpolarizability, NBO and HOMO-LUMO analysis of Pteridine2,4-dione

The FTIR and FT-Raman spectra of Pteridine2,4-dione has been recorded in the region 4000-450 and 4000-100 cm(-1), respectively. The tautomeric stability, optimized geometry, frequency and intensity of the vibrational bands of Pteridine2,4-dione were obtained by the density functional theory (DFT) using 6-311++G(d,p) basis set. 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 (1)H and(13)C NMR spectra chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The theoretical UV-Vis spectrum of the compound using CIS method and the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (β(0)) of these novel molecular system and related properties (β, α(0) and Δα) of Pteridine2,4-dione are calculated using DFT/6-311++G (d,p) method on the finite-field approach. The Mulliken charges, the values of electric dipole moment (μ) of the molecule were computed using DFT calculations. The change in electron density (ED) in the σ(*) antibonding orbitals and stabilization energies E(2) have been calculated by natural bond (NBO) analysis to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions.

Study of the solvent effects on the molecular structure and CO stretching vibrations of flurbiprofen

The effects of 15 solvents on the C=O stretching vibrational frequency of flurbiprofen (FBF) were determined to investigate solvent-solute interactions. Solvent effects on the geometry and C=O stretching vibrational frequency, ν(C=O), of FBF were studied theoretically at the DFT/B3LYP and HF level in combination with the polarizable continuum model and experimentally using attenuated total reflection infrared spectroscopy (ATR-IR). The calculated C=O stretching frequencies in the liquid phase are in agreement with experimental values. Moreover, the wavenumbers of ν(C=O) of FBF in different solvents have been obtained and correlated with the Kirkwood-Bauer-Magat equation (KBM), the solvent acceptor numbers (ANs), and the linear solvation energy relationships (LSERs). The solvent-induced stretching vibrational frequency shifts displayed a better correlation with the LSERs than with the ANs and KBM.

Vibrational and electronic absorption spectral studies of 5-amino-1-(4-bromophenyl)-3-phenyl-1-H-pyrazole

The FT-IR and FT-Raman spectra of 5-amino-1-(4-bromophenyl)-3-phenyl-1-H-pyrazole have been measured in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been carried out with the help of DFT method. The assignments of the vibrational spectra have been carried out with the normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The first-order hyperpolarizability (β(0)) and related properties (μ, α(0), and Δα) of 5A4BP3PP are calculated by using HF/6-31G(d,p) method on the finite field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bonding orbital (NBO) analysis. The results show that electron density (ED) in the σ(*) and π(*) antibonding orbitals and second order delocalization energies E(2) confirms the occurrence of the intramolecular charge transfer (ICT) within the molecule. UV-vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by TDDFT using 6-31G(d,p). The HOMO-LUMO calculations indicating the charge transfer takes place within the molecule.

Modeling the effect of H-bonding interactions and molecular packing on the molecular structure of [Ag(ethylnicotinate)(2)]NO (3) complex

The gas phase molecular structure of a single isolated molecule of [Ag(Etnic)(2)NO(3)];1 where Etnic = Ethylnicotinate was calculated using B3LYP method. The H-bonding interaction between 1 with one (complex 2) and two (complex 3) water molecules together with the dimeric formula [Ag(Etnic)(2)NO(3)](2);4 and the tetrameric formula [Ag(Etnic)(2)NO(3)](4);5 were calculated using the same level of theory to model the effect of intermolecular interactions and molecular packing on the molecular structure of the titled complex. The H-bond dissociation energies of complexes 2 and 3 were calculated to be in the range of 12.220-14.253 and 30.106-31.055 kcal mol(-1), respectively, indicating the formation of relatively strong H-bonds between 1 and water molecules. The calculations predict bidentate nitrate ligand in the case of 1 and 2, leading to distorted tetrahedral geometry around the silver ion with longer Ag-O distances in case of 2 compared to 1, while 3 has a unidentate nitrate ligand leading to a distorted trigonal planar geometry. The packing of two [Ag(Etnic)(2)NO(3)] complex units; 4 does not affect the molecular geometry around Ag(I) ion compared to 1. In the case of 5, the two asymmetric units of the formula [Ag(Etnic)(2)NO(3)] differ in the bonding mode of the nitrate group, where the geometry around the silver ion is distorted tetrahedral in one unit and trigonal planar in the other. The calculations predicted almost no change in the charge densities at the different atomic sites except at the sites involved in the C-H⋯O interactions as well as at the coordinated nitrogen of the pyridine ring.

Spectroscopic properties, NLO, HOMO-LUMO and NBO analysis of 2,5-Lutidine

In this work, FT-IR and FT-Raman spectra of 2,5-Lutidine (C(7)H(9)N) have been reported in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. Density functional theory (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 HF and B3LYP methods with 6-311++G(d,p) basis set. The complete vibrational assignments of wavenumbers have been made on the basis of potential energy distribution (PED). The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The optimized geometric parameters were compared with experimental values of 2,5-Lutidine. 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 (FMO), molecular electrostatic potential (MEP) and thermodynamic properties were performed. Mulliken charges and NBOs of the title molecule were also calculated and interpreted. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. The dipole moment, linear polarizability and first hyperpolarizability values were also computed.

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.

Molecular structure and vibrational spectra of 3-and 4-amino-2-bromopyridine by density functional methods

In this work, experimental and theoretical study on the molecular structure and the vibrational spectra of 3-amino-2-bromopyridine (Compound I) and 4-amino-2-bromopyridine (Compound II) are presented. The vibrational frequencies of these compounds were obtained theoretically by DFT/B3LYP employing the 6-311G(2df,2p) basis set for optimized geometries and were compared with Fourier Transform Infrared solid phase spectra (FTIR) in the region of 400-4000 cm(-1), FT-Raman spectra in the region of 100-4000 cm(-1) and with solution phase spectra in the region of 400-4000 cm(-1). Complete vibrational assignment, analysis and correlation of the fundamental modes for these compounds have been carried based on the potential energy distribution (PED). The vibrational harmonic frequencies were scaled using scale factors, yielding a good agreement between the experimentally recorded and the theoretically calculated values. Finally the calculated HOMO and LUMO energies are localized on the entire ring and substituents.

Single crystal structure, spectroscopic (FT-IR, FT-Raman, 1H NMR, 13C NMR) studies, physico-chemical properties and theoretical calculations of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameteres (FT-IR, FT-Raman, (1)H NMR, (13)C NMR) of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene, CNT. The optimized geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were obtained at the B3LYP/6-311++G(d,p) level of theory and thermodynamic functions were calculated at the same level. A detailed interpretation of the Infrared, Raman and NMR spectra of the compound was reported as well. Analysis of experimental NMR chemical shifts was supported by quantum chemical calculations and HOSE code fragment based prediction tool (ACD/NMR). The theoretical results showed an excellent agreement with the experimental values. The physico-chemical properties (such as logP, hydrophobicity, …) were also calculated using three commercially available programs.

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.

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.

Experimental and DFT studies on the vibrational and electronic spectra of 4,5-dihydro-6-methyl-4-[(E)-(3-pyridinylmethylene)amino]-1,2,4-triazin-3(2H)-one

Vibrational and electronic spectral measurements were made for 4,5-dihydro-6-methyl-4-[(E)-(3-pyridinylmethylene)amino]-1,2,4-triazin-3(2H)-one (pymetrozine). Optimized geometrical structure and harmonic vibrational frequencies were computed by ab initio RHF, B-based DFT methods (BLYP, BP86 and BPW91) and B3-based DFT methods (B3LYP, B3P86 and B3PW91) using 6-311++G(d,p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed both in gas-phase and in C(2)H(5)OH solution using TD-B3LYP/6-311++G(d,p) and PCM-B3LYP/6-311++G(d,p) approaches, respectively, the calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum. The MEP calculation indicates that the most possible site for electrophilic attack is H23 and the most possible sites for nucleophilic attack are N5 and O19.

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.

Ab initio HF, DFT and experimental (FT-IR) investigation of vibrational spectroscopy of P-N,N-dimethylaminobenzylidenemalononitrile (DBM)

The optimized geometry and vibrational frequencies of P-N,N-dimethylaminobenzylidenemalononitrile (DBM) were obtained by ab initio HF and DFT/B3LYP levels with complete relaxation in the potential energy surface using 6-31++G(d,p) and 6-311++G(d,p) basis sets. The Fourier-transform infrared (FT-IR) spectrum of DBM has been recorded in the region 4000-400 cm(-1). The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR spectrum. The calculated frequencies are in good agreement with the experimental frequencies.

Spectroscopic analysis of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile

The optimized geometry and vibrational frequencies of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile (DOPNA) were obtained by ab initio DFT/B3LYP level with complete relaxation in the potential energy surface using 6-31G and 6-311G basis sets. The Fourier-transform infrared (FT-IR) spectrum of DOPNA has been recorded in the region 4000-400 cm(-1). The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR spectrum. The calculated frequencies are in comparable agreement with the experimental frequencies. The calculated energy span between the HOMO and the LUMO of DOPNA is 2.94 and 2.87eV by B3LYP/6-31G and B3LYP/6-311G, respectively.

Vibrational spectroscopic (FTIR and FTRaman) investigation using ab initio (HF) and DFT (LSDA and B3LYP) analysis on the structure of Toluic acid

The FTRaman and FTIR spectra for Toluic acid (TA) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using HF/DFT (LSDA and B3LYP) method BY employing 6-311G (d, p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by HF and DFT (LSDA/B3LYP) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for benzoic acid and some substituted benzoic acids. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from HF and DFT. The scaled vibrational frequencies at 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 TA are effected upon profusely with the methyl substitutions in comparison to benzoic acid and these differences are interpreted.

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.

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.

Molecular structure, vibrational spectroscopic (FT-IR, FT-Raman), UV and NBO analysis of 2-chlorobenzonitrile by density functional method

In this work, we will report a combined experimental and theoretical study on molecular structure, vibrational spectra, NBO and UV spectral analysis of 2-chlorobenzonitrile (2-ClBN). The FT-IR solid phase (4000-400 cm(-1)), and FT-Raman spectra (3500-50 cm(-1)) of 2-ClBN was recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2-ClBN in the ground state have been calculated by using the density functional methods (BLYP, B3LYP) with 6-31G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and π* anti bonding orbitals and E2 energies confirms the occurrence of ICT (Intra molecular Charge Transfer) within the molecule. The UV spectrum was measured in ethanol solution. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. Finally calculated results were applied to simulated Infrared and Raman spectra of the title compound which show good agreement with observed spectra.

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.