Molecular Structure, Spectroscopic(FT-IR,FT-Raman, NMR,UV), HOMO- LUMO Analysis of 1-Bromo-4-Nitrobenzene by Quantum Computational Methods (original) (raw)
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This work presents the solid phase FTIR and FT-Raman spectra of 1-Bromo-4-Nitrobenzene (1B4NB) were recorded in the regions 4000-400 cm-1 and 3500-50 cm-1, respectively. The fundamental vibrational frequencies and intensities of the vibrational bands were calculated using density functional theory (DFT) with B3LYP method and standard 6-311++G (d, p) basis set combinations. The infrared and Raman spectra were also predicted from the calculated intensities. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. Comparison of simulated spectra with the experimental spectra provided important information about the ability of the computational method to describe the vibrational modes. The calculated and observed frequencies are found to be in good agreement. The theoretical UV-Vis spectrum of the compound and the electronic properties, such as HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies were obtained by TD-DFT approach. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of 1B4NB were calculated using the Guauge Independent Atomic Orbital (GIAO) method. The Mullikan charges of the molecule were computed using DFT calculations. The chemical reactivity and Thermodynamic properties of 1B4NB at different temperatures were also calculated. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping molecular electron density isosurface with the molecular electrostatic potential. Key Words: Vibrational spectra, 1B4NB, FTIR, FT Raman, TD-DFT, HOMO, LUMO.
The FTIR and FT Raman spectra of 1-4-Dichloro-2-NitroBenzene (14DC2NB) have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1 respectively. The optimized geometry ,frequency and intensity of the vibrational bands of 1-4-Dichloro-2-NitroBenzene (14DC2NB) was obtained by the Density functional theory (DFT)using the basis set 6-31g(d,p). The harmonic vibrational frequencies were calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The Calculated and Observed frequencies are found to be in good agreement. UV-Visible spectrum of the compound was recorded, the electronic properties and HOMO-LUMO energies were calculated by Time Dependent DFT (TD-DFT) approach. A detailed interpretation of the infrared and Raman spectra were also reported based on Potential Energy Distribution (PED). The 1 H and 13 C nuclear magnetic resonance (NMR) chemical shifts of 14DC2NB were calculated using the GIAO approach by applying B3LYP method. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The Chemical reactivity and Thermodynamic properties of 14DC2NB at different temperatures were also calculated.
This work deals with the vibrational spectroscopy of 1-chloro-4-nitrobenzene (1C4NB) by means of quantum chemical calculations. The solid phase FT-IR and FT-Raman spectra of 1-chloro-4-nitrobenzene (1C4NB) have been recorded in the regions 4000–400 and 3500-50 cm −1 respectively. The fundamental vibrational frequencies and intensities of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311+G(d.p) method and frequencies were scaled using various scale factors. Simulation of infrared and Raman spectra utilizing the results of these calculations led to excellent overall agreement with the observed spectral patterns. The SQM approach applying selective scaling of the DFT force field was shown to be superior to the uniform scaling method in its ability to allow for making modifications in the band assignment, resulting in more accurate simulation of FT-IR and FT-Raman Spectra. The 1 H and 13 C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The theoretical and experimental UV–VIS spectra of 1-chloro-4-nitrobenzene (1C4NB) were recorded and compared and the electronic properties, such as HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) energies were performed by time-dependent DFT (TD-DFT) approach. Information about the size, shape and charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with Molecular Electro Static Potential (MESP).The dipole moment , polarizability, first order hyperpolarizability and mullikkan atomic charges of the title molecule were computed using DFT calculations. In addition Chemical reactivity and thermodynamic properties of 1C4NB at different temperatures were also computed.
Computational and Theoretical Chemistry, 2011
The molecular properties and harmonic wavenumbers of 3-(2-methoxyphenoxy) propane-1,2-diol have been calculated using ab initio and density functional theory. The polarizability and first static hyperpolarizability of the title molecule have been calculated at different basis sets. In general a good agreement between experimental and calculated normal modes has been observed. The frontier orbital and molecular electrostatic potential surface study has also been employed to understand the active sites of 3-(2methoxyphenoxy) propane-1,2-diol. PACS: 31.15.A, 31.15.es, 31.15.ap ½½ Key words: Density functional theory, frontier orbital energy gap, first static hyperpolarizability ½¾ ½¿ 1 Introduction ½ With the standard quantum chemical models (i.e., without the inclusion of parity violation), ½ there is no difference whatsoever in energetics, vibrational frequencies, polarizabilities, NMR ½ spectra, or any other non-chiral property for a given pair, i.e., (R) and (S) forms of enan-½ tiomers [1-4]. Differences in the properties of enantiomers arise either only within chiral en-½ vironments or interactions with other chiral compounds. The present investigation therefore ½ deals with the quantum chemical study of molecular structural, energetic and vibrational data ¾¼ of one of the pair i.e., (R) enantiomer of 3-(2-methoxyphenoxy) propane-1,2-diol [MPPD], in ¾½ gas phase, due to its biological and pharmaceutical importance. The drug MPPD, also known ¾¾ as guaifenesin, is an expectorant, used extensively in anti-tussive and is capable of increasing ¾¿ the excretion of phlegm from the respiratory tract. Bredikhin and others have carried out ¾ * Corresponding author. Email address: ÓÒ ÖÔÖ × ½ Ñ ÐºÓÑ (O. Prasad) http://www.global-sci.org/jams 212 c 2011 Global-Science Press L. Sinha, A. Kumar, V. Narayan, et al. / J. At. Mol. Sci. 2 (2011) 212-224 213 extensive studies on the structure, solid state properties and issues related to the effective ¾ resolution procedure for MPPD [5-7]. ¾ The vibrational spectroscopic analysis is known to provide immensely invaluable molecu-¾ lar structure elucidation in synergy with quantum chemical calculations. In order to obtain a ¾ complete description of molecular dynamics, vibrational wavenumber calculations along with ¾ the normal mode analysis have been carried out at the DFT level employing the basis set ¿¼ 6-311+G(2d,2p). The optimized geometry of molecule under investigation and its molecu-¿½ lar properties such as equilibrium energy, frontier orbital energy gap, molecular electrostatic ¿¾ potential energy map, dipole moment, polarizability, first static hyperpolarizability have also ¿¿ been used to understand the properties and active sites of the drug. ¿ 2 Experimental ¿ 2.1 Structure and Spectra ¿
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2013
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 are investigated by FT-IR, FT-Raman and UV-Vis techniques. The FT-IR and FT-Raman spectra of the title compound have been recorded in the region 4000-400 cm-1 and 4000-100 cm-1 respectively. The UV-Vis absorption spectrum of the HEHMPT that dissolved in water is recorded in the range of 100-400 nm. The structural and spectroscopic data of the molecule are obtained from B3LYP and M06-2X with 6-31G(d,p) basis set calculations. The theoretical wavenumbers are scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments are performed on the basis of the normal coordinate analysis (NCA), experimental result 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 is analyzed by NBO analysis. The molecule orbital contributions are 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 are reported. The calculated HOMO and LUMO energies show that charge transfer interactions taking place within the molecule. Mulliken population analysis on atomic charges is also calculated.
Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile butadiene rubber. So we have done a vibrational spectroscopic investigation on 5-Bromobenzene-1, 3-dicarbonitrile which has a nitrile group. The optimized geometry of the 5-Bromobenzene-1, 3-dicarbonitrile molecule has been determined by the method of density functional theory (DFT). For both geometry and total energy, it has been combined with B3LYP functional having 6-311 g (d, p) as the basis set. Using this optimized structure, we have calculated the infrared wave numbers, which are very useful in absence of experimental data. On Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of 5-Bromobenzene-1, 3-dicarbonitrile. A complete assignment is provided for the observed FTIR spectra.
The spectra of 1-bromo-4-methylnaphthalene have been analyzed in the region 4000–400 and 4000–100 cm−1for FTIR and FT-Raman respectively. The optimized geometry, fundamental vibrational frequency and intensity of the vibrational bands of title compound were evaluated using ab initio HF and density functional theory (DFT) levels of theory 6-311G basis set. The Calculated harmonic vibrational frequencies were scaled and the values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies were found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed spectrograms. Mullikan atomic charge were calculated and interpreted. A study on the electronic properties, such as HOMO and LUMO energies were performed by time independent DFT approach. In addition, molecular electrostatic potential (MEP) and thermodynamic properties were performed. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by gauge independent atomic orbital (GIAO) method and compared with experimental chemical shift of closely related molecules. First order hyperpolarizability and polarizability of title compound were calculated using HF theory. Thermodynamic calculations of title compound were also performed with different temperature.
International Journal of Quantum Chemistry, 2006
Geometry, vibrational wavenumbers, and several thermodynamic parameters have been calculated using ab initio quantum chemical methods for the 3‐aminobenzonitrile molecule for the first time. The results were compared with experimental values. With the help of specific scaling procedures, the observed vibrational wavenumbers were analyzed and assigned to different normal modes of the molecule. In general, the error obtained was very low. Using potential energy distribution (PED), the contributions of the different modes to each wavenumber were determined. Other general conclusions were also deduced. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006