Aid Of Normal Coordinate Analysis Research Articles

Density functional study on the structural conformations, intramolecular charge transfer and vibrational spectra of 4-hydroxy-3-methoxy-5-nitrobenzaldehyde

Abstract In this paper, we report a combined experimental and theoretical study on molecular structure; vibrational spectra of 4-hydroxy-3-methoxy-5-nitrobenzaldehyde (HMN) have been recorded using Fourier transform infrared spectroscopy (FT-IR) and FT-Raman measurements in the region of 4000–400 cm −1 and 3500–100 cm −1 , respectively. The molecular geometry, harmonic vibrational frequencies, bonding features, total energy, Mulliken atomic charges and thermodynamic properties for most stable conformer of HMN in ground state were obtained by density functional theory (DFT) with the standard B3LYP/6-311++G(d,p) basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled quantum mechanical force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed good agreement with the observed spectra. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule.

Intramolecular Charge Transfer and Z-Scan Studies of a Semiorganic Nonlinear Optical Material Sodium Acid Phthalate Hemihydrate: A Vibrational Spectroscopic Study

FT-IR and Raman spectra of the nonlinear optical material sodium acid phthalate hemihydrate crystal have been recorded and analyzed. The equilibrium geometry, bonding features, and harmonic vibrational wavenumbers have been investigated with the help of the B3LYP density functional theory method. A detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. The natural bond orbital analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule. Nonlinear optical absorption of the sample has been studied at 532 nm using single 5 ns laser pulses, employing the open-aperture Z-scan technique. It is found that the NaAPH molecule is a potential candidate for optical limiting applications.

A characterization study on 2,6-dimethyl-4-nitropyridine N-oxide by density functional theory calculations

This study deals with the identification of a title compound, 2,6-dimethyl-4-nitropyridine N-oxide by means of theoretical calculations. The optimized molecular structures, vibrational frequencies, corresponding vibrational assignments, thermodynamic properties and atomic charges of the title compound in the ground state were evaluated using density functional theory (DFT) with the standard B3LYP/6-311G(d,p) method and basis set combination for the first time. Theoretical vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results show that the optimized geometric parameters (bond lengths and bond angles) and vibrational frequencies were observed to be in good agreement with the available experimental results. Based on the results of comparison between experimental results and theoretical data, the chosen calculation level is powerful approach for understanding the molecular structures and vibrational spectra of the 2,6-dimethyl-4-nitropyridine N-oxide. Moreover, we not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also determined the transition state and energy band gap. Based on the investigations, the title compound is found to be useful to bond metallically and interact intermolecularly. Infrared intensities and Raman activities were also reported.

Experimental and theoretical studies on the identification of p-biphenyloxycarbonylphenyl acrylate

This study presents the identification of a title compound, p-biphenyloxycarbonylphenyl acrylate by means of experimental and theoretical evidences. The spectroscopic properties of the compound were experimentally investigated by Fourier transformation-infrared spectra (in the region 400–4000 cm −1) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz). Moreover, the optimized molecular structures, vibrational frequencies including infrared intensities and Raman activities, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, thermodynamic properties, atomic charges and ultraviolet–visible (UV–vis) spectra were analyzed utilizing ab initio Hartree–Fock (HF) and Density Functional Theory (B3LYP) methods at 6-31G(d,p) calculation level. It was found that the vibrational frequencies and chemical shifts obtained were shown to have a good agreement with available experimental results. We not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also evaluated the transition state and energy band gap clearly.

Density functional theory study on the identification of 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol

This study deals with the identification of a title compound, 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol by means of quantum chemical calculations. The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments, thermodynamic properties, charge analyses, nuclear magnetic resonance (NMR) chemical shifts and ultraviolet–visible (UV–vis) spectra of the title molecule in the ground state were evaluated using density functional theory (DFT) with the standard B3LYP/6-311++G(d,p) method and basis set combination for the first time. Theoretical vibrational spectra of the title compound were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results show that the obtained optimized geometric parameters (bond lengths, bond angles and bond dihedrals) and vibrational frequencies were observed to be in good agreement with the available experimental results. Moreover, the calculations of the electronic spectra, 13C and 1H chemical shifts were compared with the experimental ones. Furthermore, we not only simulated the frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also determined the transition states and energy band gaps, as well. It was found that charge analyses supported the evidences of MEP. Infrared intensities and Raman activities were also reported.

Electronic absorption, vibrational spectra and nonlinear optical properties of N-(2 chlorophenyl)-1-propanamide

FT-Raman, IR and UV–vis spectroscopies have been applied to investigate the potential nonlinear optical (NLO) material N-(2 chlorophenyl)-1-propanamide. A detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. Density functional theory is applied to explore the nonlinear optical properties of the molecule. The study suggests the importance of π-conjugated systems for nonlinear optical properties and the possibility of charge transfer interactions. Good consistency is found between the calculated results and experimental data for the electronic absorption, IR and Raman spectra. The solvent effects have been calculated using time-dependent density functional theory in combination with the polarized continuum model, and the results are in good agreement with experimental measurements.

Electronic and structural effects on the nonlinear optical behavior in π‐conjugated structure bis(4‐nitrophenyl) carbonate: a vibrational spectroscopic approach

AbstractFourier transform (FT)‐Raman and infrared (IR) spectra of the nonlinear optical (NLO) material bis(4‐nitrophenyl) carbonate were recorded and analyzed. The geometry, first hyperpolarizability and harmonic vibrational wavenumbers were calculated with the help of Becke3–Lee–Yang–Parr density functional theory method. The detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. The second‐order NLO properties of the molecule were studied by the Kurtz and Perry powder reflection technique. Stability of the molecule arising from hyperconjugative interactions leading to its NLO activity and charge delocalization were analyzed using natural bond orbital analysis. Copyright © 2010 John Wiley & Sons, Ltd.

Vibrational spectra and first-order molecular hyperpolarizabilities of p-hydroxybenzaldehyde dimer

Single crystals of p-hydroxybenzaldehyde (PHBA) were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. The density functional theoretical (DFT) computations were also performed at the B3LYP/6-311++G(d,p) level to derive the equilibrium geometry, vibrational wavenumbers and intensities. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. The various intramolecular interactions that is responsible for the stabilization of the molecule was revealed by natural bond orbital analysis. Vibrational analysis based on the NIR-FT-Raman, FT-IR and computed spectrum reveals that the CH in-plane bending of the aldehyde group interacts with its stretching mode via Fermi Resonance and evidence for intermolecular interaction can be well identified as two CH bands in IR spectra at 2740 and 2804 cm −1 aldehyde group of the p-hydroxybenzaldehyde dimer. The red shift of the O–H stretching wavenumber is due to the formation of strong O–H⋯O hydrogen bonds by hyperconjugation between the carbonyl oxygen lone electron pairs and the O–H σ * anti-bonding orbitals.

Molecular structure and vibrational spectroscopic investigation of 4-chloro-4′dimethylamino-benzylidene aniline using density functional theory

The Fourier Transform Raman and infrared spectra of the crystallized 4-chloro-4′dimethylamino-benzylidine aniline (CDMABA) have been recorded in the region 3500–200 cm −1 and 4000–400 cm −1, respectively. The geometry optimization, electrostatic potential surface and vibrational wavenumbers with Raman scattering activities and infrared absorption intensities have been investigated by density functional theory (DFT) method using 6-311++G(d,p) basis set and Becke’s three-parameters hybrid functional (B3LYP). The calculated molecular geometry has been compared with the experimental data obtained from XRD. The assignments of the vibrational spectra have been carried out with the aid of normal coordinate analysis (NCA). The natural bond orbital analysis (NBO) has been performed in order to study the intramolecular bonding, interactions among bonds and delocalization of unpaired electrons. The electrostatic potential surface mapped with isodensity surface has been obtained.

Structure and vibrational frequencies of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione based on density functional theory calculations: The role of π-electron conjugation and back-donation

This work deals with the vibrational spectroscopy of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione by means of quantum chemical calculations. The mid and far FT-IR and FT-Raman spectra are recorded in the condensed State. The fundamental vibrational frequencies and intensity of vibrational bands are evaluated using density functional theory (DFT) with the standard B3LYP/6-31G* method and basis set combination and is scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectrum is interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results of the calculations are applied to simulate infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The infrared unscaled frequencies and intensities are used to disentangle the role played by back-donation in the title compound. For this purpose five other molecules are considered as references: ethane, dimethyl ether, anisole, p-nitro-anisole, and p-hydroxyanisole, in which back-donation has already been ascertained also experimentally. From the study of infrared intensities it is shown that no back-donation of electrons from the oxygen lone pairs takes place, independently of the conformation of the methoxy-group.

Vibrational contributions to the second-order nonlinear optical properties of π-conjugated structure acetoacetanilide

FT-Raman and IR spectra of the nonlinear optic (NLO) crystal, acetoacetanilide have been recorded and analyzed. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. The various intramolecular interactions that is responsible for the stabilization of the molecule was revealed by natural bond orbital analysis. The Kurtz and Perry powder reflection technique appeared to be very effective in studies of second-order nonlinear optical properties of the molecule.

Electronic absorption and vibrational spectra and nonlinear optical properties of 4-methoxy-2-nitroaniline

FT-Raman, IR and UV-vis spectroscopies have been applied to investigate the potential nonlinear optical (NLO) material 4-methoxy-2-nitroaniline. A detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. Density functional theory is applied to explore the nonlinear optical properties of the molecule. The study suggests the importance of pi-conjugated systems for nonlinear optical properties and the possibility of charge transfer interactions. Good consistency is found between the calculated results and experimental data for the electronic absorption, IR and Raman spectra. The solvent effects have been calculated using time-dependent density functional theory in combination with the polarized continuum model, and the results are in good agreement with experimental measurements. The calculations reveal that incorporation of substituents (amino, nitro and methoxy) has a strong influence on the structure and spectroscopic properties of the molecule, and the effect of electron charge transfer was examined by natural bond orbital population analysis.

Scaled Quantum FT‐IR and FT‐Raman Spectral Analysis of 1‐Methoxynaphthalene

The structural and vibrational property of 1‐methoxynaphthalene has been studied. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using B3LYP/6‐31G (d, p) basis set and was scaled using various scale factors, which yielded a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis. The results of the calculations were applied to simulated spectra of the title compound, which shows excellent agreement with observed spectra. The calculated force constants in vibrational internal coordinates are in closely coincides with the experimentally observed force constants.

Simulation of IR and Raman spectra of p-hydroxyanisole and p-nitroanisole based on scaled DFT force fields and their vibrational assignments

This work deals with the vibrational spectroscopy of p-hydroxyanisole (PHA) and p-nitroanisole (PNA) by means of quantum chemical calculations. The mid and far FT-IR and FT-Raman spectra were recorded in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-31G* method and basis set combination and were scaled using various scale factors which yield a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results of the calculations were applied to simulate infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra.

Density functional theory calculations and vibrational spectra of 2‐bromo‐4‐chloro phenol and 2‐chloro‐4‐nitro phenol

AbstractFTIR and FT Raman spectra of 2‐bromo‐4‐chloro phenol (BCP) and 2‐chloro‐4‐nitro phenol (CNP) were recorded in the region 4000–400 and 4000–50 cm−1, respectively. The molecular structure, geometry optimization, and vibrational wavenumbers were investigated. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using the standard B3LYP/6‐31G** method and basis set combination and was scaled using multiple scale factors, which yield good agreement between the observed and calculated wavenumbers. The results of the calculations are applied to simulate the infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.

A joint FTIR, FT‐Raman and scaled quantum mechanical study of 1,3‐dibromo‐2,4,5,6‐tetra‐fluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB)

AbstractThe liquid phase FTIR and FT‐Raman spectra of 1,3‐dibromo‐2,4,5,6‐tetrafluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB) were recorded in the regions 4000–400 cm−1 and 4000–50 cm−1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure opti1mization and force field calculations based on the density functional theory using the standard B3LYP/6‐31G* method and basis set combination. The scaled force field reproduced the experimental wavenumbers of the molecule for DTFB and PFB, respectively. The effects of halogen substituents on the structure and vibrational wavenumbers have been investigated. Assignments of fundamental modes were made based on the comparison between calculated and experimental results. Copyright © 2009 John Wiley & Sons, Ltd.

Vibrational spectra and scaled quantum chemical studies of the structure of Martius yellow sodium salt monohydrate

AbstractThe FT‐IR and Raman spectra of Martius Yellow sodium salt Monohydrate (MYM) [2, 4‐dinitro‐1‐naphthol sodium salt] in solid‐phase have been measured. The geometry, intramolecular hydrogen bonding and harmonic vibrational wavenumbers of MYM have been investigated with the help of B3LYP density functional theory (DFT) methods. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The existence of intramolecular CH···O improper, blue‐shifted hydrogen bonding was investigated by means of the NBO analysis. The infrared and Raman spectra were predicted theoretically from the calculated intensities. The observed and the calculated spectra were found to be in good agreement. Copyright © 2009 John Wiley & Sons, Ltd.

Density functional theory calculations and vibrational spectra of p‐bromonitrobenzene

AbstractFT‐IR and FT‐Raman spectra of p‐bromonitrobenzene (p‐BNB) have been recorded in the region 4000–400 cm−1 and 4000–50 cm−1, respectively. The molecular structure, geometry optimization, vibrational wavenumbers have been investigated. The spectra were interpreted with the aid of normal coordinate analysis based on the density functional theory (DFT) using the standard B3LYP/6‐31G method and basis set combination and was scaled using multiple scale factors yielding good agreement between observed and calculated wavenumbers. The results of the calculations are applied to simulate infrared and Raman spectra of the title compound which showed reasonable agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.

FTIR, FT-Raman, scaled quantum chemical studies of the structure and vibrational spectra of 1,5-dinitronaphthalene

The solid phase FTIR and FT-Raman spectra of 1,5-dinitronaphthalene (DNN) have been recorded in the regions 4000–50 and 3500–100 cm −1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculation based on density functional theory using standard B3LYP/6-31G* and B3LYP/6-311+G** methods and basis set combinations and was scaled using various scale factors yielding fairly good agreement between observed and calculated frequencies. Based on the present good quality scaled quantum mechanical force field, a reliable description of the fundamentals was provided and the assignments have been proposed with the help of normal coordinate analysis. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.

Vibrational spectra and potential energy distributions for 1‐benzyl‐1H‐imidazole by normal coordinate analysis

AbstractThe Fourier‐transform (FT) Raman and infrared (IR) spectra of the crystallized novel pharmaceutical molecule 1‐benzyl‐1H‐imidazole (BI) were recorded and analyzed. The geometry, intermolecular hydrogen bond, and harmonic vibrational wavenumbers of BI were investigated with the help of B3PW91 density functional theory (DFT) methods. The detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The aromaticities of the imidazole and phenyl rings were studied using the standard harmonic oscillator model of aromaticity (HOMA) index. Natural bond orbital (NBO) analysis on BI was carried out to demonstrate the various intramolecular interactions that are responsible for the stabilization of this molecule leading to its medicinal activity. The potential energy profile corresponding to the torsion around the bridge bonds connecting the two rings was drawn to explain the steric and/or electronic effects using potential energy surface (PES) scan studies. The pronounced double‐bond localization in the imidazole ring upon intermolecular H‐bonding appears to be the cause for its enhanced aromaticity. Copyright © 2008 John Wiley & Sons, Ltd.