Vibrational assignments for 7-methyl-4-bromomethylcoumarin, as aided by RHF and B3LYP/6-31G* calculations

Increasing gold nanostars SERS response with silver shells: a surface-based seed-growth approach

A straightforward method to prepare surface enhanced Raman spectroscopy (SERS) chips containing a monolayer of silver coated gold nanostars (GNS@Ag) grafted on a glass surface is introduced. The synthetic approach is based on a seed growth method performed directly on surface, using GNS as seeds, and involving a green pathway, which only uses silver nitate, ascorbic acid and water, to grow the silver shell. The preparation was optimized to maximize signals obtaining a SERS response of one order of magnitude greater than that from the original GNS based chips, offering in the meantime good homogeneity and acceptable reproducibility. The proposed GNS@Ag SERS chips are able to detect pesticide thiram down to 20 ppb.

Surface-Enhanced Raman Spectroscopy Chips Based on Silver Coated Gold Nanostars

Surface-enhanced Raman scattering (SERS) is becoming widely used as an analytical tool, and the search for stable and highly responsive SERS substrates able to give ultralow detection of pollutants is a current challenge. In this paper we boosted the SERS response of Gold nanostars (GNS) demonstrating that their coating with a layer of silver having a proper thickness produces a 7-fold increase in SERS signals. Glass supported monolayers of these GNS@Ag were then prepared using simple alcoxyliane chemistry, yielding efficient and reproducible SERS chips, which were tested for the detection of molecules representative of different classes of pollutants. Among them, norfloxacin was detected down to 3 ppb, which is one of the lowest limits of detection obtained with this technique for the analyte.

Quantum chemical calculation, performance of selective antimicrobial activity using molecular docking analysis, RDG and experimental (FT-IR, FT-Raman) investigation of 4-[{2-[3-(4-chlorophenyl)-5-(4-propan-2-yl) phenyl)-4, 5-dihydro- 1H- pyrazol-1-yl]-4-oxo-1, 3- thiazol-5(4H)-ylidene} methyl] benzonitrile

The research received a great deal of worldwide attention due to the nature of interpretation before the experimental process. Based on the systematic process the structure of thiazole -pyrazole compound 4-[{2-[3-(4-chlorophenyl)-5-(4-propan-2-yl) phenyl)-4, 5-dihydro- 1H- pyrazol-1-yl]-4-oxo-1, 3- thiazol-5(4H)-ylidene} methyl] benzonitrile [CPTBN] was investigated. In the first level, the spectral statistics on experimental FT-IR and FT- Raman was reported. At the next level, geometrical parameters was theoretically acquired from density functional theory (DFT) using B3LPY/6-31G and 6-311G basis set. The computed Wavenumber were collected and compared with the experimental data. The vibrational modes were interpreted in terms of potential energy distribution (PED) results. The FMO, MEP, and NBO analysis further validated the electrophilic and nucleophilic interaction in the molecular systems. Two grams-positive bacteria: staphylococcus aureus, Bacillus subtilis and two gram-negative bacteria: Esherichia coli, Pseudomonas aeruginosa was performed for antibacterial activity. Two fungal strain Candida albicans and Aspergillus Niger was carried out against a ligand using anti-fungal activity. The molecular docking analysis explores the antimicrobial and selective potential inhibitory nature of the binding molecule. Besides, RDG and ELF analysis were also performed to show the nature of interactions between the molecule.

Influence of the long-range ordering of gold-coated Si nanowires on SERS

Controlling the location and the distribution of hot spots is a crucial aspect in the fabrication of surface-enhanced Raman spectroscopy (SERS) substrates for bio-analytical applications. The choice of a suitable method to tailor the dimensions and the position of plasmonic nanostructures becomes fundamental to provide SERS substrates with significant signal enhancement, homogeneity and reproducibility. In the present work, we studied the influence of the long-range ordering of different flexible gold-coated Si nanowires arrays on the SERS activity. The substrates are made by nanosphere lithography and metal-assisted chemical etching. The degree of order is quantitatively evaluated through the correlation length (ξ) as a function of the nanosphere spin-coating speed. Our findings showed a linear increase of the SERS signal for increasing values of ξ, coherently with a more ordered and dense distribution of hot spots on the surface. The substrate with the largest ξ of 1100 nm showed an enhancement factor of 2.6 · 10³ and remarkable homogeneity over square-millimetres area. The variability of the signal across the substrate was also investigated by means of a 2D chemical imaging approach and a standard methodology for its practical calculation is proposed for a coherent comparison among the data reported in literature.

Tunable coating of gold nanostars: tailoring robust SERS labels for cell imaging

Surface modification of noble metal nanoparticles with mixed molecular monolayers is one of the most powerful tools in nanotechnology, and is used to impart and tune new complex surface properties. In imaging techniques based on surface enhanced Raman spectroscopy (SERS), precise and controllable surface modifications are needed to carefully design reproducible, robust and adjustable SERS nanoprobes. We report here the attainment of SERS labels based on gold nanostars (GNSs) coated with a mixed monolayer composed of a poly ethylene glycol (PEG) thiol (neutral or negatively charged) that ensure stability in biological environments, and of a signalling unit 7-Mercapto-4-methylcoumarin as a Raman reporter molecule. The composition of the coating mixture is precisely controlled using an original method, allowing the modulation of the SERS intensity and ensuring overall nanoprobe stability. The further addition of a positively charged layer of poly (allylamine hydrocloride) on the surface of negatively charged SERS labels does not change the SERS response, but it promotes the penetration of GNSs in SH-SY5Y neuroblastoma cells. As an example of an application of such an approach, we demonstrate here the internalization of these new labels by means of visualization of cell morphology obtained with SERS mapping.

Combined spectroscopic and DFT studies on 6-bromo-4-chloro-3-formyl coumarin

The FTIR and FT-Raman spectra of 6-bromo-4-chloro-3-formyl coumarin (6B4C3FC) have been recorded in the region 4000-400 and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands were obtained by the density functional theory (DFT) using 6-31G(d,p) basis set. The harmonic vibrational frequencies were scaled and compared with experimental values. The observed and the calculated frequencies were found to be in good agreement. The UV-Visible spectrum was also recorded and compared with the theoretical values. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (β0) of 6B4C3FC is 21 times greater than that of urea. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. Information about the charge density distribution of the molecule and its chemical reactivity has been obtained by mapping molecular electrostatic potential surface. In addition, the non-linear optical properties were discussed from the dipole moment values and the excitation wavelength in the UV-Visible region.

Quantum chemical computations, vibrational spectroscopic studies, NLO and NBO/NLMO analysis of o-chlorobenzohydrazide

The molecular vibrations of o-chlorobenzohydrazide (OCBH) have been investigated in polycrystalline sample, at room temperature, by recording Fourier transform infrared (FT-IR) and FT-Raman spectroscopies. The complete vibrational assignment and analysis of the fundamental modes was carried out using the experimental data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the HF and DFT/B3LYP calculations employing 6-311++G(d,p) basis set. The (1)H and (13)C NMR chemical shifts have been simulated. Thermodynamic properties have been calculated at different temperatures. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis.

Density functional theory investigations on the conformational stability, molecular structure and vibrational spectra of 6-methyl-2-chromenone

The Fourier-transform infrared and FT-Raman spectra of 6-methyl-2-chromenone (6M2C) was 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 6M2C were carried out by density functional theory (DFT/B3LYP and LSDA) method with 6-311++G(d,p) basis set. 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 6M2C might have microscopic non-linear optical (NLO) behaviour with non-zero values. A detailed interpretation of infrared and Raman spectra of 6M2C is also reported. The calculated HOMO-LUMO energy gap shows that charge transfer occur within the molecule. The molecular electrostatic potential map shows that the negative potential sites are on the electronegative atoms as well as the positive potential sites are around the hydrogen atoms. The NMR spectrum is used in conjunction with other forms of spectroscopy and chemical analysis to determinate the structures of complicated organic molecules.

Molecular structure, vibrational investigation of 2-chloro-α-α-α-trifluoro-3,5-dinitrotoluene using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) and UV-Vis absorption spectra in organic solvents: a IEF-PCM/TD-DFT study

Theoretical Spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. The effect of solvent polarity on the optimized structure is studied by the density functional theory calculation (LSDA, B3LYP, B3PW91 and MPW1PW91 with 6-311++G(d,p)) in gas phase and selected solvents benzene (non-polar solvent), tetrahydrofuran THF (polar aprotic solvent), DMSO, Methanol (polar solvent) and water (protic solvent). In addition variation of dipole moment and charges on atoms in the solvents are studied. With the help of TD-DFT study, the electrostatic effects of different solvents and the energy difference between the excited electronic states noticeably depends on the size of the solute cavity used in the PCM calculations. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated in gas phase, reverling the correlations between standard heat capacities (C), standard entropies (S), standard enthalpy (H) and vibrational and rotational temperatures. The solvation influence on the geometrical parameters, atomic charges and HOMO-LUMO energies was estimated with the use of PCM method. The presence of solvent did not alter these parameters, but affected the orbital energies. The aggregation phenomena were studied with dimer and trimer structure of the title compound.

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.

Vibrational spectra, structural conformations, scaled quantum chemical calculations and NBO analysis of 3-acetyl-7-methoxycoumarin

The powder form NIR-FT Raman and FT-IR spectra of 3-acetyl-7-methoxycoumarin (3A7MC) have been recorded in the regions 4000-400 and 3500-100 cm(-1), respectively. The equilibrium geometry, vibrational frequencies, band intensities, NMR spectra, NBO analysis and UV-Vis spectral studies of the most stable conformer have been calculated by density functional B3LYP method with the 6-311G(d,p) basis set. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra, the calculated wavenumber and intensity of the vibrational bands and the potential energy distribution over the internal coordinates. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping the electron density isosurface with electrostatic potential surfaces (ESP). Natural bond orbital analysis has been carried out to understand the nature of different interactions responsible for the electron delocalization and the intramolecular charge transfer between the orbitals (n→π(∗), n→σ(∗), π→π(∗)).

FT-IR, FT-Raman and UV-Vis spectra and DFT calculations of 3-cyano-4-methylcoumarin

The vibrational and electronic spectra of 3-cyano-4-methylcoumarin (3C4MC) are reported and discussed. In this work the structural properties, vibrational frequencies and electronic spectra of 3C4MC have been investigated extensively using density functional theory (DFT) employing B3LYP exchange correlation with the normal basis level 6-31G(d,p). NBO and HOMO, LUMO analysis has been carried out. The geometries and normal modes of vibrations obtained from B3LYP calculations are in good agreement with the experimentally observed data.

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.

Spectroscopic (FT-IR, FT-Raman, UV and NMR) investigation and NLO, HOMO-LUMO, NBO analysis of organic 2,4,5-trichloroaniline

In this work, the experimental and theoretical study on the molecular structure and vibrational spectra of 2,4,5-trichloroaniline (C(6)H(4)NCl(3), abbreviated as 2,4,5-TClA) were studied. The FT-IR and FT-Raman spectra were recorded. The molecular geometry and vibrational frequencies in the ground state were calculated by using the Hartree-Fock (HF) and density functional theory (DFT) methods (B3LYP) with 6-311++G(d,p) basis set. Comparison of the observed fundamental vibrational frequencies of 2,4,5-TClA with calculated results by HF and DFT indicates that B3LYP is superior to HF method for molecular vibrational problems. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The theoretically predicted FT-IR and FT-Raman spectra of the title molecule have been constructed. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. Besides, molecular electrostatic potential (MEP) and thermodynamic properties were performed. The electric dipole moment (μ) and the first hyperpolarizability (β) values of the investigated molecule were computed using ab initio quantum mechanical calculations. The calculated results also show that the 2,4,5-TClA molecule may have microscopic nonlinear optical (NLO) behavior with non-zero values. Mulliken atomic charges of 2,4,5-TClA was calculated and compared with aniline and chlorobenzene molecules. The (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 spectroscopic properties of anticancer drug Apigenin investigated by using DFT calculations, FT-IR, FT-Raman and NMR analysis

The FT-Raman and FT-Infrared spectra of solid Apigenin sample were measured in order to elucidate the spectroscopic properties of title molecule in the spectral range of 3500-50 cm(-1) and 4000-400 cm(-1), respectively. The recorded FT-IR and FT-Raman spectral measurements favor the calculated (by B3LYP/6-31G(d,p) method) structural parameters which are further supported by spectral simulation. Additional support is given by the collected (1)H and (13)C NMR spectra recorded with the sample dissolved in DMSO. The predicted chemical shifts at the B3LYP/6-31G(d) level obtained using the Gauge-Invariant Atomic Orbitals (GIAO) method with and without inclusion of solvent using the Polarizable Continuum Model (PCM). By using TD-DFT method, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental one is determined. The UV-visible absorption spectra of the compound that dissolved in Ethanol, Methanol and DMSO were recorded in the range of 800-200 nm. The formation of hydrogen bond and the most possible interaction are explained using natural bond orbital (NBO) analysis. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis and atomic charges of the title compound were investigated using theoretical calculations. The results are discussed herein and compared with similar molecules whenever appropriate.

Analysis of vibrational spectra (FT-IR and FT-Raman) and nonlinear optical properties of organic 2-chloro-p-xylene

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 100-4000cm(-1) and 400-4000cm(-1) respectively, for the title molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree-Fock (HF) and density functional theory (DFT) method with 6-311++G(d,p) basis set. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other method. The influences due to the substitution of halogen bond and methyl group were investigated. The results of the calculations are applied to simulate the vibrational spectra of the title compound, which show excellent agreement with observed spectra. The absorption energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT). Besides, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), and thermodynamic properties were performed. Mulliken charges of the title molecule were also calculated and interpreted. The dipole moment, linear polarizability and first hyperpolarizability values were also computed.

Vibrational spectroscopic studies, NLO, HOMO-LUMO and electronic structure calculations of α,α,α-trichlorotoluene using HF and DFT

FT-IR and FT-Raman spectra of α,α,α-trichlorotoluene have been recorded and analyzed. The geometry, fundamental vibrational frequencies are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) B3LYP/6-311++G(d,p) method and a comparative study between HF level and various basis sets combination. The fundamental vibrational wavenumbers as well as their intensities were calculated and a good agreement between observed and scaled calculated wavenumbers has been achieved. The complete vibrational assignments of wavenumbers are made on the basis of potential energy distribution (PED). The effects due to the substitutions of methyl group and halogen were investigated. The absorption energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT). The electric dipole moment, polarizability and the first hyperpolarizability values of the α,α,α-trichlorotoluene have been calculated. (1)H NMR chemical shifts were calculated by using the gauge independent atomic orbital (GIAO) method with HF and B3LYP methods with 6-311++G(d,p) basis set. Moreover, molecular electrostatic potential (MEP) and thermodynamic properties were performed. Mulliken and natural charges of the title molecule were also calculated and interpreted.

Density functional theory study on characterization of 3-chloro-1,2-benzisothiazole

The FT-IR and FT-Raman spectra of 3-chloro-1,2-benzisothiazole (CBT) have been recorded and analyzed. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of density functional theory (DFT) gradient calculations, using 6-311++G(d,p) basis set. Mulliken population analysis shows charge distribution on the molecule. Thermodynamic properties like entropy, heat capacity, zero point energy have been calculated for the molecule. The calculated HOMO and LUMO energies show the charge transfer occurs within the molecule. Stability of the molecule has been analyzed using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis. The results of the calculations were applied to simulated spectra of the title compound, which show the excellent agreement with the observed spectra.

FT-IR, FT-Raman, ab initio, HF and DFT studies, NBO, HOMO-LUMO and electronic structure calculations on 4-chloro-3-nitrotoluene

In this work, the vibrational spectral analysis was carried out by using Raman and infrared spectroscopy in the range 100-4000 cm(-1) and 50-4000 cm(-1), respectively, for 4-chloro-3-nitrotoluene (C7H6NO2Cl) molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree Fock (HF) and density functional theory (DFT) method and different basis sets combination. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The calculated HOMO and LUMO energies shows that charge transfer within the molecule. The effects due to the substitutions of methyl group, nitro group and halogen were investigated. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) and thermodynamic properties were performed.

FT-IR, FT-Raman and UV spectral investigation: computed frequency estimation analysis and electronic structure calculations on chlorobenzene using HF and DFT

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 100-4000 cm(-1) and 400-4000 cm(-1) respectively, for the title molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree Fock (HF) and density functional theory (DFT) method and different basis sets combination. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The effects due to the substitution of halogen bond were investigated. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), and thermodynamic properties were performed. The thermodynamic properties of the title compound at different temperatures have been calculated, revealing the correlations between heat capacity (C), entropy (S), and enthalpy changes (H) and temperatures.

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.

DFT-based molecular modeling, NBO analysis and vibrational spectroscopic study of 3-(bromoacetyl)coumarin

The NIR-FT Raman and FT-IR spectra of 3-(bromoacetyl)coumarin (BAC) molecule have been recorded and analyzed. Density functional theory (DFT) calculation of two BAC conformers has been performed to find the optimized structures and computed vibrational wavenumbers of the most stable one. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Characteristic vibrational bands of the pyrone ring and methylene and carbonyl groups have been identified. The lowering of HOMO-LUMO energy gap clearly explains the charge transfer interactions taking place within the molecule.

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.

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.

Vibrational spectroscopic analysis of 2-chlorotoluene and 2-bromotoluene: a combined experimental and theoretical study

In this work, the vibrational spectral analysis was carried out using Raman and infrared spectroscopy in the range 100-4000 cm(-1) and 50-4000 cm(-1), respectively, for the title molecules. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartee Fock (HF) and density functional theory (DFT) method and different basis sets combination. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The effects due to the substitutions of methyl group and halogen bond were investigated. The results of the calculations were applied to simulated spectra of the title compounds, which show excellent agreement with observed spectra.

Vibrational and ab initio studies of 3-acetyl-6-bromocoumarin and 3-acetyl-6-methylcoumarin

Infrared absorption and Raman spectra (3500-50 cm(-1)) of 3-acetyl-6-bromocoumarin and 3-acetyl-6-methylcoumarin have been measured and interpreted, aided by electronic structure calculations at RHF and B3LYP using 6-31(d, p) basis set. It has been determined that the rotation of the acetyl group with respect to the coumarin ring results in three conformers--two trans and one cis--for each molecule, with one trans conformer being the most stable in both cases. There are significant changes in the vibrational structure as characterized by positions and intensities of certain modes in going from 3-acetyl-6-bromocoumarin to 3-acetyl-6-methylcoumarin. The carbonyl stretching mode of the pyrone ring is stable in both molecules whereas the same mode in acetyl groups is not. Ring stretching vibrations are coupled to C-H in-plane bending vibrations. Down-shifting of frequencies of methyl vibrations in acetyl group occurs vis-à-vis methyl vibrations in 3-acetyl-6-methylcoumarin. A strong Raman band at 126 cm(-1) in both molecules is structure-independent non-genuine mode, correlated to lattice vibrations in the solid phase.

Vibrational spectra, normal modes, ab initio and DFT calculations for 6-Chloro- and 7-Chloro-4-bromomethylcoumarins

Vibration spectral measurements - Infrared (4000-400 cm(-1)) and Raman (3500-50 cm(-1)) spectra - have been made for the solid samples of 6-Chloro- and 7-Chloro-4-bromomethylcoumarins. Ground electronic state energies, equilibrium geometries, harmonic vibrational spectra and normal modes have been computed using ab initio - RHF/6-31G* - and DFT - B3LYP/6-31G* levels of theory. The optimization yielded three structures for each molecule, with one being a transition state structure. Of the remaining two conformers, one belongs to C(s) symmetry and the other belongs to C(1), the latter being the most stable one. The optimized dihedral angle for -CH(2)Br group is 111 degrees in agreement with X-ray diffraction results reported for the similar molecular systems. Assignment of all the observed spectral bands has been proposed. The absorptions show band pattern revealing isomer characteristics and vibrational coupling in varying degrees; the Raman spectra show structural changes associated with the rings as well as lattice modes.

Experimental and theoretical study on molecular structure and FT-IR, Raman, NMR spectra of 4,4'-dibromodiphenyl ether

In this work, both experimental and theoretical study on the FT-IR and Raman spectra as well as (1)H NMR and (13)C NMR chemical shifts of 4,4'-dibromodiphenyl ether have been carried out. The optimized geometry was obtained by using both HF and density functional B3LYP method with the 6-31G(d) and 6-311+G(d, p) basis sets. The calculated bond lengths and dihedral angles for both methods on 6-31G(d) level show the best agreement with the experimental data, while the dihedral angles of C(1')-O-C(1)-C(6) and C(1')-O-C(1)-C(2), critical geometry parameters for conformers in the ground state, indicates significant deviation of HF results from the experimental information. The harmonic vibration frequencies and intensities in IR and Raman spectra and chemical shifts of the molecule were calculated on the B3LYP/6-31G(d) and B3LYP/6-311+G(d, p) levels. The scaled theoretical vibration frequencies present good agreement with the experimental values. The larger basis set makes no significant improvement in the accuracy of the vibration frequencies. Besides, chemical shifts of hydrogen and carbon computed on B3LYP/6-31G(d) level agree well with the observations.

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.