Theoretical Wavenumbers Research Articles

Vibrational spectroscopic study and NBO analysis on tranexamic acid using DFT method

In this work, we reported the vibrational spectra of tranexamic acid (TA) by experimental and quantum chemical calculation. The solid phase FT-Raman and FT-IR spectra of the title compound were recorded in the region 4000cm−1 to 100cm−1 and 4000cm−1 to 400cm−1 respectively. The molecular geometry, harmonic vibrational frequencies and bonding features of TA in the ground state have been calculated by using density functional theory (DFT) B3LYP method with standard 6-31G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The vibrational assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the σ* and π* antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. The electrostatic potential mapped onto an isodensity surface has been obtained. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase.

Vibrational spectra, monomer, dimer, NBO, HOMO, LUMO and NMR analyses of trans-4-hydroxy-l-proline

This work presents the characterization of trans-4-hydroxy-l-proline (abbreviated as THLP) by quantum chemical calculations and spectral techniques. The spectroscopic properties were investigated by FT-IR, FT-Raman and 1H and 13C nuclear magnetic resonance (NMR) techniques. The FT-IR (4000–400cm−1) and FT-Raman (3500–10cm−1) spectra in the solid phase were recorded for THLP. The 1H and 13C NMR spectra were recorded in DMSO solution. The energies of THLP are obtained for all the eight conformers form density functional theory (DFT) with 6-311++G(d,p) basis set calculations. From the computational results, C1 conformer is identified as the most stable conformer of THLP. The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the experimental results and potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method in terms of fundamental modes. 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 HOMO–LUMO energies reveal charges transfer occurs within the molecule. The isotropic chemical shift computed by 1H and 13C NMR chemical shifts of the THLF, calculated using the gauge invariant atomic orbital (GIAO) method also shows good agreement with experimental observations.

Synthesis, FTIR and FT-Raman spectral analysis and structure–activity relations of N-(4-bromophenyl)-2,2-dichloroacetamide by DFT studies

The FTIR and FT-Raman vibrational spectra of N-(4-bromophenyl)-2,2-dichloroacetamide molecule has been recorded and analysed the complete vibrational fundamental modes of the most stable geometry of the compound using the experimental FTIR and FT-Raman data on the basis of peak positions, relative intensities and quantum chemical studies. The observed vibrational frequencies were compared with the theoretical wavenumbers of the optimised geometry of the compound obtained from the DFT-B3LYP gradient calculations employing the high level 6-311++G** and cc-pVTZ basis sets. The effect of substituent Br in the amide moiety have been analysed and compared. The kinetic and thermodynamic stability and chemical reactivity descriptors of the molecule have been determined. The reactive centres are found from the molecular electrostatic potential and the atomic charges. The limits of electrostatic potential are −9.617e×10−3 and +9.617e×10−3. The molecule has great electronegativity difference, charge is very polarized, and there are significant differences in electron density in different regions of the molecule. The lone pair donor orbital,nN→π*COinteraction possess a strong stabilisation of 64.21kcalmol−1.

Normal Modes, Molecular Orbitals and Thermochemical Analyses of 2,4 and 3,4 Dichloro Substituted Phenyl-N-(1,3-thiazol-2-yl)acetamides: DFT Study and FTIR Spectra

A detailed spectroscopic analysis of two dichloro substituted phenyl-N-(1,3-thiazol-2-yl)acetamides at 2,4 and 3,4 positions of the phenyl ring has been carried out by using B3LYP method with 6-31+G(d, p) basis set within density functional scheme. The scaled theoretical wave numbers are in perfect agreement with the experimental values and the vibrational modes are interpreted in terms of potential energy distribution (PED). The internal coordinates are optimized repeatedly to maximize the PED contributions. The molecular HOMO-LUMO surfaces, their respective energy gaps, and MESP surfaces have also been drawn to explain the chemical activity of both molecules. Various thermodynamic parameters are presented at the same level of theory.

Theoretical anharmonic Raman and infrared spectra with vibrational assignments and NBO analysis for 1-methyl-4-nitropyrazole

Both experimental and calculated spectral and electronic properties of 1-methyl-4-nitropyrazole have been demonstrated. Experimental values have been compared with theoretical computations and also new hybrid density functionals, APF (Austin–Petersson–Frisch) and APF(D), have been tested and compared to B3LYP hybrid functional. The theoretical wavenumbers of fully anharmonic infrared and Raman spectra with anharmonic intensities of 1-methyl-4-nitropyrazole are in very good agreement with the experimental observations. The detailed interpretation of the infrared and Raman spectra is reported based on potential energy distribution (PED). The ring N1N2 bond distance of 1-methyl-4-nitropyrazole, calculated with both APF/6-311++G(df,pd) and APF-D/6-311++G(df,pd) models, is much underestimated in comparison with X-ray experimental value. Overall results point that B3LYP functional with 6-311++G(df,pd) basis function better predicts the bond lengths and angles of titled compound than both APF and APF-D ones. As a key factor for biological activity of nitro compounds, the redox potential of 1-methyl-4-nitropyrazole in water solution was also measured and then was set against the calculated electronic properties. The analysis of the calculated components of HOMO and LUMO orbitals has shown that nitrogen and oxygen atoms of nitro group are the most probable site of acceptance of electron. Hence, nitro group should be the most sensitive fragment of 1-methyl-4-nitropyrazole molecule to the reduction process. Moreover, the stability of the 1-methyl-4-nitropyrazole arising from hyper conjugative interactions has been studied using natural bond orbital (NBO) analysis. Unambiguous assignment of values of proton chemical shifts to appropriate protons has been finally made thanks to two dimensional (2D) 1H–1H NMR spectroscopy.

FT-IR, FT-Raman spectra and other molecular properties of 2,4- dichlorobenzonitrile: A interpretation by a DFT study

FT-IR and FT-Raman spectra of 2,4-dichlorobenzonitrile at room temperature have been recorded in the regions 200–3500cm−1 and 0–3400cm−1, respectively. The observed vibrational bands were analyzed and assigned to different normal modes of the molecule according to the Wilson’s notation. Density functional calculations were performed to support our frequency assignments. Specific scale equations deduced from the benzene molecule were employed to improve the calculated values. For the majority of the normal modes, the deviations between the corresponding experimental and scaled theoretical wavenumbers are located in the expected range. A correct characterization of each normal mode is of vital importance in the assignment of the observed bands, and the same has been successfully done by the aid of Potential Energy Distributions (PEDs) calculated separately for each normal mode of 2,4-dichlorobenzonitrile. The molecular structure was optimized and several thermodynamic parameters were determined. HOMO and LUMO orbital energy analysis were carried out.

Raman study of ACu3Fe4O12 (A = Ca, Sr, Y and Eu)

A vibrational study of ACu3Fe4O12 (A = Ca, Sr, Y and Eu) compounds was carried out by means of micro-Raman scattering and lattice dynamics calculations. Polarized Raman scattering measurements were performed on rectangular microcrystals, with sizes close to 7 μm, and six Raman active modes were observed among the eight expected. It was then possible to assign the observed modes to the correct symmetry. Moreover, lattice dynamics calculations led to determine the main atomic displacements and a good agreement was found between experimental and theoretical wavenumbers. Furthermore, wavenumbers evolution versus A cation showed two behaviors separating the samples into two groups.

DFT computations and spectroscopic analysis of p-bromoacetanilide

This work presents the characterization of p-bromoacetanilide (PBA) by quantum chemical calculations and spectral techniques. The spectroscopic properties were investigated by FT-IR, FT-Raman and UV–Vis techniques. The structural and spectroscopic data of the molecule were obtained from B3LYP/6-311++ G(d,p) and MPW1PW91/6-311++G(d,p) basis set calculations. The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the normal co-ordinate analysis (NCA), experimental results and potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method, interpreted in terms of fundamental modes. The stability of molecule has been analyzed by NBO/NLMO analysis. The molecular orbital contributions were studied by using the density of states. The electronic properties like UV–Vis spectral analysis and HOMO–LUMO energies were reported. The calculated HOMO and LUMO energies shows that charge transfer interactions taking place within the molecule. Mulliken population analysis on atomic charges, Statistical thermodynamic properties at various temperatures of the PBA is also calculated.

Identification of structural and spectral features of synthesized cyano-stilbene dye derivatives: A comparative experimental and DFT study

The synthesized three dye derivatives of cyano-stilbene monomer were identified by experimental spectroscopic techniques and density functional approach. The optimized geometrical structure, vibrational and electronic transitions along with the nonlinear optical (NLO) properties of those compounds were presented in this study. The vibrational spectra of investigated compounds were recorded in solid state with FT-IR and FT-Raman spectrometry in the range of 4000–400cm−1 and 3600–50cm−1, respectively. The theoretical ground state equilibrium conformations and vibrational wavenumbers were carried out by using density functional method with 6-311G(d,p) basis set. Assignments of the fundamental vibrational modes were examined on the basis of the measured data and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. The UV absorption spectra of monomers were observed in the range of 200–600nm in chloroform, acetonitrile and toluene, and time dependent DFT method was used to obtain the electronic properties. The linear polarizability and first hyperpolarizability of the studied molecules indicates that the title compounds can be used as a good nonlinear optical material. A detailed description of spectroscopic behaviors of compounds was given based on the comparison of experimental measurements and theoretical computations.

Molecular orbital studies (hardness, chemical potential, electronegativity and electrophilicity), vibrational spectroscopic investigation and normal coordinate analysis of 5-{1-hydroxy-2-[(propan-2-yl)amino]ethyl}benzene-1,3-diol

FT-IR and FT-Raman spectra of 5-{1-hydroxy-2-[(propan-2-yl) amino] ethyl} benzene-1,3-diol (abbrevi- 54 ated as HPAEBD) were recorded in the region 4000–450cm−1 and 4000–100cm−1 respectively. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (B3LYP) and HF method with 6-31 G(d,p) as basis set. The theoretical wave numbers were scaled and compared with experimental FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated Potential energy distribution (PED). Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ antibonding orbitals and E (2) energies confirm the occurrence of intra molecular charge transfer (ICT) within the molecule. The molecule orbital contributions were studied by using the total (TDOS), sum of α and β electron (αβDOS) density of States. Mulliken population analysis of atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule. The electron density-based local reactivity descriptors such as Fukui functions were calculated to explain the chemical selectivity or reactivity site in this compound. On the basis of vibrational analyses, the thermodynamic properties of title compound at different temperatures have been calculated.

Quantum mechanical and spectroscopic (FT-IR, 13C, 1H NMR and UV) investigations of potent antiepileptic drug 1-(4-chloro-phenyl)-3-phenyl-succinimide

This study represents an integrated approach towards understanding the vibrational, electronic, NMR, and structural aspects, and reactivity of 1-(4-chloro-phenyl)-3-phenyl-succinimide (CPPS). A detailed interpretation of the FT-IR, UV and NMR spectra were reported. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated with the help of density functional theory (DFT) B3LYP method using 6-31G(d,p) and 6-311++G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Invariant Atomic Orbital (GIAO) method. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the σ* and π* antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of 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 calculated by Time-Dependent DFT (TD-DFT) approach. To estimate chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of the molecule.

FT-IR, FT-Raman spectra and other molecular properties of 3,5-dichlorobenzonitrile: A DFT study

The IR and Raman spectra of 3,5-dichlorobenzonitrile (3,5-DCBN) molecule were recorded at room temperature and then the assignment of the observed fundamental bands were achieved by the aid of the theoretical vibrational spectral data obtained from a quantum chemical study carried out for the free molecule case. In the calculations performed to determine the molecular geometry, vibrational spectral data and thermodynamic parameters, Møller–Plesset second order perturbation theory (MP2) and hybrid Density Functional Theory (DFT) types of electronic structure methods, B3LYP and B3PW91, were used. The overestimations of the calculated harmonic wavenumbers were efficiently corrected by the aid of a specific scaling procedure. This empirical scaling process significantly increased the reliability of our assignments and analyses on the observed bands due to different vibrational normal modes of the molecule. For the majority of the normal modes, the deviations between the corresponding experimental and scaled theoretical wavenumbers have located in the expected range. A correct characterization of the normal modes is of vital importance in the assignment of the observed bands, and this was successfully done by the aid of the Potential Energy Distributions (PEDs) separately calculated for each normal mode of 3,5-DCBN.

Vibrational Spectra of Two Narcotics-A DFT Study

This work deals with the theoretical study of the molecular structure and vibrational spectra of two well known narcotics-heroin and morphine. The spectra were interpreted with the aid of normal mode analysis following full structure optimization based on the density functional theory and the 6-311G (d, p) basis set combination. A detailed interpretation of the infrared spectra of morphine and heroin is also reported in the present work. The similarities and differences between the vibrational spectra of the two molecules studied have been highlighted. The scaled theoretical wave numbers are in perfect agreement with the experimental values. The thermodynamical calculations related to the two narcotics, namely heroi n and morphine, were also performed at the B3LYP/6-311G (d, p) theoretical level.

Structural, spectral, optical and antimicrobial properties of synthesized 1-benzoyl-3-furan-2-ylmethyl-thiourea

The 1-benzoyl-3-furan-2-ylmethyl-thiourea (bftu) was synthesized and its structure was determined by elemental analyses, IR spectroscopy, 1H and 13C NMR spectroscopy and single crystal X-ray diffraction analysis. Also its antimicrobial activity was determined. We analyzed the optimized geometric structure and energies of bftu in the ground state as theoretically. Theoretical calculations were performed at the DFT level. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution (TED). The nuclear magnetic resonance (NMR) chemical shifts of bftu molecule were calculated using the gauge-invariant-atomic orbital (GIAO) method in acetone solution and compared with the experimental data. The dipole moment, linear polarizability and first hyper polarizability values were also computed.

Experimental (FT-IR, FT-Raman, 1H, 13C NMR) and theoretical study of alkali metal syringates

In this work the influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of the syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid) was studied. This paper presents spectroscopic vibrations (FT-IR, FT-Raman) and NMR (1H and 13C) study of the series of alkali metal syringates from lithium to cesium syringates. Characteristic shifts of band wavenumbers and changes in band intensities along the metal series were observed. Optimized geometrical structures of the studied compounds were calculated by the B3LYP method using the 6-311++G∗∗ basis set. Aromaticity indices, atomic charges, dipole moments and energies were also calculated. The theoretical wavenumbers and intensities of IR and NMR spectra were obtained. The calculated parameters were compared to experimental characteristics of studied compounds.

Structural and vibrational studies of the potential anticancer agent, 5-difluoromethyl-1,3,4-thiadiazole-2-amino by DFT calculations

The structural and vibrational properties of a potential anticancer agent, the 5-difluoromethyl-1,3,4 thiadiazole-2- amino derivative and its tautomeric forms were studied by using the available experimental infrared and 1H, 13C and 19F NMR spectra and theoretical calculations based the density functional theory (DFT). The bonds order, atomic charges, charge-transfers and topological properties were studied by means of the Natural Bond Orbital (NBO) and the Atoms in Molecules theory (AIM) calculations. The harmonic vibrational wavenumbers for the optimized geometries were calculated at B3LYP/6-31G∗ and B3LYP/6-311++G∗∗ levels. For a complete assignment of the compound infrared spectrum, the DFT calculations were combined with Pulay’s scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumbers values to the experimental ones. The results were then used to predict the Raman spectra, for which there are no experimental data. An agreement between theoretical and available experimental results was found and a complete assignment of all the observed bands in the vibrational spectra was performed. The theoretical vibrational calculations allowed us to obtain a set of scaled force constants fitting the observed wavenumbers. Additionally, the frontier molecular HOMO and LUMO orbitals for the compound were analyzed and compared with those calculated for the 2-amino-1,3,4 thiadiazole molecule. The calculated 1H, 13C and 19F chemicals shifts are in good agreement with the corresponding experimental NMR spectra of the compound in solution.

Spectroscopic studies (FTIR, FT-Raman and UV), potential energy surface scan, normal coordinate analysis and NBO analysis of (2R,3R,4R,5S)-1-(2-hydroxyethyl)-2-(hydroxymethyl) piperidine-3,4,5-triol by DFT methods

This work presents the characterization of (2R,3R,4R,5S)-1-(2-hydroxyethyl)-2-(hydroxymethyl)piperidine-3,4,5-triol (abbreviated as HEHMPT) by quantum chemical calculations and spectral techniques. The spectroscopic properties were investigated by FT-IR, FT-Raman and UV–Vis techniques. The FT-IR spectrum (4000–400cm−1) and FT-Raman spectrum (4000–100cm−1) in solid phase was recorded for HEHMPT. The UV–Vis absorption spectrum of the HEHMPT that dissolved in water was recorded in the range of 100–400nm. The structural and spectroscopic data of the molecule were obtained from B3LYP and M06-2X with 6-31G(d,p) basis set calculations. The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the normal co-ordinate analysis (NCA), experimental results and potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method, interpreted in terms of fundamental modes. The stable geometry of the compound has been determined from the potential energy surface scan. The stability of molecule has been analyzed by NBO analysis. The molecule orbital contributions were studied by using the total (TDOS), partial (PDOS), and overlap population (OPDOS) density of states. The electronic properties like UV spectral analysis and HOMO–LUMO energies were reported. The calculated HOMO and LUMO energies shows that charge transfer interactions taking place within the molecule. Mulliken population analysis on atomic charges is also calculated.

Structural, vibrational and nuclear magnetic resonance investigations of 4-bromoisoquinoline by experimental and theoretical DFT methods

Quantum chemical calculations of energy, structural parameters and vibrational wavenumbers of 4-bromoisoquinoline (4BIQ) were carried out by using B3LYP method using 6-311++G**, cc-pVTZ and LANL2DZ basis sets. The optimised geometrical parameters obtained by DFT calculations are in good agreement with electron diffraction data. Interpretations of the experimental FTIR and FT-Raman spectra have been reported with the aid of the theoretical wavenumbers. The differences between the observed and scaled wavenumber values of most of the fundamentals are very small. The thermodynamic parameters have also been computed. Electronic properties of the molecule were discussed through the molecular electrostatic potential surface, HOMO–LUMO energy gap and NBO analysis. To provide precise assignments of 1H and 13CNMR spectra, isotropic shielding and chemical shifts were calculated with the Gauge-Invariant Atomic Orbital (GIAO) method.

Synthesis, Structural Study and Spectroscopic Characterization of a Quinolin-8-Yloxy Derivative with Potential Biological Properties

We have prepared the (5-chloro-quinolin-8-yloxy) acetic acid and characterized it by using infrared, Raman and multi-dimensional nuclear magnetic resonance spectroscopies. The density functional theory (DFT) together with the 6-31G* and 6-311++G** basis sets were used to study its structure and vibrational properties. Three stable conformations of the compound were theoretically determined in gas phase and probably these conformations are present in the solid phase. The harmonic vibrational wavenumbers for the optimized geometries were calculated at the same theory levels. For a complete assignment of the observed bands in the vibrational spectra, the DFT calculations were combined with Pulay’s scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental ones. Besides, the force constants of the three conformers of (5-chloro-quinolin-8-yloxy) acetic acid were calculated and compared with those obtained by us for the 2-(quinolin-8-yloxy) acetic acid. In addition, the characteristics of the electronic delocalization of those structures were performed by using natural bond orbital (NBO), while the corresponding topological properties of electronic charge density are analysed by employing Bader’s atoms in molecules theory (AIM).

Experimental and theoretical study on benzoic acid derivatives

Benzoic (BA), p-hydroxybenzoic (HBA), m-methoxybenzoic (MBA), vanillic (VA) and syringic (SGA) acids were studied using both experimental and theoretical tools. The vibrational (FT-IR, FT-Raman) and 1H and 13C NMR spectra of benzoic acid derivatives were recorded. Characteristic shifts and changes in intensities of bands along the studied series were observed. The changes of chemical shifts of protons (1H NMR) and carbons (13C NMR) in the series of studied compounds were observed too. Optimized geometrical structures of studied compounds were obtained by B3LYP method using 6-31++G**, 6-311+G** and 6-311++G** basis sets. Aromaticity indices, atomic charges, dipole moments and energies were calculated. The theoretical chemical shifts in 1H and 13C NMR spectra and theoretical wavenumbers and intensities of IR and Raman spectra were determined. The calculated parameters were compared to experimental characteristic of studied compounds.